Landlock fix for v7.0-rc6
-----BEGIN PGP SIGNATURE----- iIYEABYKAC4WIQSVyBthFV4iTW/VU1/l49DojIL20gUCacVk0xAcbWljQGRpZ2lr b2QubmV0AAoJEOXj0OiMgvbS0v4A/joA39PP40bpHZorGYVgHyEZZgCgGicffmYd TnvlvawOAPoDc6h1HwkcOonhYgvEe29JPIBrEFOCNBZsGTntvN29Ag== =T4m+ -----END PGP SIGNATURE----- Merge tag 'landlock-7.0-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/mic/linux Pull Landlock fixes from Mickaël Salaün: "This mainly fixes Landlock TSYNC issues related to interrupts and unexpected task exit. Other fixes touch documentation and sample, and a new test extends coverage" * tag 'landlock-7.0-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/mic/linux: landlock: Expand restrict flags example for ABI version 8 selftests/landlock: Test tsync interruption and cancellation paths landlock: Clean up interrupted thread logic in TSYNC landlock: Serialize TSYNC thread restriction samples/landlock: Bump ABI version to 8 landlock: Improve TSYNC types landlock: Fully release unused TSYNC work entries landlock: Fix formatting
This commit is contained in:
Linus Torvalds
commit
25b69ebe28
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@ -8,7 +8,7 @@ Landlock: unprivileged access control
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=====================================
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:Author: Mickaël Salaün
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:Date: January 2026
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:Date: March 2026
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The goal of Landlock is to enable restriction of ambient rights (e.g. global
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filesystem or network access) for a set of processes. Because Landlock
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@ -197,12 +197,27 @@ similar backwards compatibility check is needed for the restrict flags
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.. code-block:: c
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__u32 restrict_flags = LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON;
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if (abi < 7) {
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/* Clear logging flags unsupported before ABI 7. */
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__u32 restrict_flags =
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LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON |
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LANDLOCK_RESTRICT_SELF_TSYNC;
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switch (abi) {
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case 1 ... 6:
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/* Removes logging flags for ABI < 7 */
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restrict_flags &= ~(LANDLOCK_RESTRICT_SELF_LOG_SAME_EXEC_OFF |
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LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON |
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LANDLOCK_RESTRICT_SELF_LOG_SUBDOMAINS_OFF);
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__attribute__((fallthrough));
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case 7:
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/*
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* Removes multithreaded enforcement flag for ABI < 8
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*
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* WARNING: Without this flag, calling landlock_restrict_self(2) is
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* only equivalent if the calling process is single-threaded. Below
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* ABI v8 (and as of ABI v8, when not using this flag), a Landlock
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* policy would only be enforced for the calling thread and its
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* children (and not for all threads, including parents and siblings).
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*/
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restrict_flags &= ~LANDLOCK_RESTRICT_SELF_TSYNC;
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}
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The next step is to restrict the current thread from gaining more privileges
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@ -299,7 +299,7 @@ out_unset:
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/* clang-format on */
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#define LANDLOCK_ABI_LAST 7
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#define LANDLOCK_ABI_LAST 8
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#define XSTR(s) #s
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#define STR(s) XSTR(s)
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@ -436,7 +436,8 @@ int main(const int argc, char *const argv[], char *const *const envp)
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/* Removes LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON for ABI < 7 */
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supported_restrict_flags &=
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~LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON;
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__attribute__((fallthrough));
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case 7:
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/* Must be printed for any ABI < LANDLOCK_ABI_LAST. */
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fprintf(stderr,
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"Hint: You should update the running kernel "
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@ -94,8 +94,7 @@ static struct landlock_details *get_current_details(void)
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* allocate with GFP_KERNEL_ACCOUNT because it is independent from the
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* caller.
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*/
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details =
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kzalloc_flex(*details, exe_path, path_size);
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details = kzalloc_flex(*details, exe_path, path_size);
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if (!details)
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return ERR_PTR(-ENOMEM);
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@ -32,9 +32,8 @@ static struct landlock_ruleset *create_ruleset(const u32 num_layers)
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{
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struct landlock_ruleset *new_ruleset;
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new_ruleset =
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kzalloc_flex(*new_ruleset, access_masks, num_layers,
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GFP_KERNEL_ACCOUNT);
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new_ruleset = kzalloc_flex(*new_ruleset, access_masks, num_layers,
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GFP_KERNEL_ACCOUNT);
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if (!new_ruleset)
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return ERR_PTR(-ENOMEM);
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refcount_set(&new_ruleset->usage, 1);
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@ -559,8 +558,8 @@ landlock_merge_ruleset(struct landlock_ruleset *const parent,
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if (IS_ERR(new_dom))
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return new_dom;
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new_dom->hierarchy = kzalloc_obj(*new_dom->hierarchy,
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GFP_KERNEL_ACCOUNT);
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new_dom->hierarchy =
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kzalloc_obj(*new_dom->hierarchy, GFP_KERNEL_ACCOUNT);
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if (!new_dom->hierarchy)
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return ERR_PTR(-ENOMEM);
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@ -203,6 +203,40 @@ static struct tsync_work *tsync_works_provide(struct tsync_works *s,
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return ctx;
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}
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/**
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* tsync_works_trim - Put the last tsync_work element
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*
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* @s: TSYNC works to trim.
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*
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* Put the last task and decrement the size of @s.
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*
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* This helper does not cancel a running task, but just reset the last element
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* to zero.
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*/
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static void tsync_works_trim(struct tsync_works *s)
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{
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struct tsync_work *ctx;
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if (WARN_ON_ONCE(s->size <= 0))
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return;
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ctx = s->works[s->size - 1];
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/*
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* For consistency, remove the task from ctx so that it does not look like
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* we handed it a task_work.
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*/
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put_task_struct(ctx->task);
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*ctx = (typeof(*ctx)){};
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/*
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* Cancel the tsync_works_provide() change to recycle the reserved memory
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* for the next thread, if any. This also ensures that cancel_tsync_works()
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* and tsync_works_release() do not see any NULL task pointers.
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*/
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s->size--;
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}
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/*
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* tsync_works_grow_by - preallocates space for n more contexts in s
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*
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@ -256,13 +290,14 @@ static int tsync_works_grow_by(struct tsync_works *s, size_t n, gfp_t flags)
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* tsync_works_contains - checks for presence of task in s
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*/
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static bool tsync_works_contains_task(const struct tsync_works *s,
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struct task_struct *task)
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const struct task_struct *task)
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{
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size_t i;
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for (i = 0; i < s->size; i++)
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if (s->works[i]->task == task)
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return true;
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return false;
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}
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@ -276,7 +311,7 @@ static void tsync_works_release(struct tsync_works *s)
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size_t i;
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for (i = 0; i < s->size; i++) {
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if (!s->works[i]->task)
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if (WARN_ON_ONCE(!s->works[i]->task))
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continue;
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put_task_struct(s->works[i]->task);
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@ -284,6 +319,7 @@ static void tsync_works_release(struct tsync_works *s)
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for (i = 0; i < s->capacity; i++)
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kfree(s->works[i]);
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kfree(s->works);
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s->works = NULL;
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s->size = 0;
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@ -295,7 +331,7 @@ static void tsync_works_release(struct tsync_works *s)
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*/
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static size_t count_additional_threads(const struct tsync_works *works)
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{
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struct task_struct *thread, *caller;
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const struct task_struct *caller, *thread;
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size_t n = 0;
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caller = current;
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@ -334,7 +370,8 @@ static bool schedule_task_work(struct tsync_works *works,
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struct tsync_shared_context *shared_ctx)
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{
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int err;
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struct task_struct *thread, *caller;
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const struct task_struct *caller;
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struct task_struct *thread;
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struct tsync_work *ctx;
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bool found_more_threads = false;
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@ -379,16 +416,14 @@ static bool schedule_task_work(struct tsync_works *works,
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init_task_work(&ctx->work, restrict_one_thread_callback);
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err = task_work_add(thread, &ctx->work, TWA_SIGNAL);
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if (err) {
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if (unlikely(err)) {
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/*
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* task_work_add() only fails if the task is about to exit. We
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* checked that earlier, but it can happen as a race. Resume
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* without setting an error, as the task is probably gone in the
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* next loop iteration. For consistency, remove the task from ctx
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* so that it does not look like we handed it a task_work.
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* next loop iteration.
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*/
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put_task_struct(ctx->task);
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ctx->task = NULL;
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tsync_works_trim(works);
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atomic_dec(&shared_ctx->num_preparing);
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atomic_dec(&shared_ctx->num_unfinished);
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@ -406,12 +441,15 @@ static bool schedule_task_work(struct tsync_works *works,
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* shared_ctx->num_preparing and shared_ctx->num_unfished and mark the two
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* completions if needed, as if the task was never scheduled.
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*/
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static void cancel_tsync_works(struct tsync_works *works,
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static void cancel_tsync_works(const struct tsync_works *works,
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struct tsync_shared_context *shared_ctx)
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{
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int i;
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size_t i;
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for (i = 0; i < works->size; i++) {
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if (WARN_ON_ONCE(!works->works[i]->task))
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continue;
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if (!task_work_cancel(works->works[i]->task,
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&works->works[i]->work))
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continue;
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@ -447,6 +485,16 @@ int landlock_restrict_sibling_threads(const struct cred *old_cred,
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shared_ctx.new_cred = new_cred;
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shared_ctx.set_no_new_privs = task_no_new_privs(current);
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/*
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* Serialize concurrent TSYNC operations to prevent deadlocks when
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* multiple threads call landlock_restrict_self() simultaneously.
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* If the lock is already held, we gracefully yield by restarting the
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* syscall. This allows the current thread to process pending
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* task_works before retrying.
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*/
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if (!down_write_trylock(¤t->signal->exec_update_lock))
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return restart_syscall();
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/*
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* We schedule a pseudo-signal task_work for each of the calling task's
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* sibling threads. In the task work, each thread:
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@ -527,24 +575,30 @@ int landlock_restrict_sibling_threads(const struct cred *old_cred,
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-ERESTARTNOINTR);
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/*
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* Cancel task works for tasks that did not start running yet,
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* and decrement all_prepared and num_unfinished accordingly.
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* Opportunistic improvement: try to cancel task
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* works for tasks that did not start running
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* yet. We do not have a guarantee that it
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* cancels any of the enqueued task works
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* because task_work_run() might already have
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* dequeued them.
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*/
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cancel_tsync_works(&works, &shared_ctx);
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/*
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* The remaining task works have started running, so waiting for
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* their completion will finish.
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* Break the loop with error. The cleanup code
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* after the loop unblocks the remaining
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* task_works.
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*/
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wait_for_completion(&shared_ctx.all_prepared);
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break;
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}
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}
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} while (found_more_threads &&
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!atomic_read(&shared_ctx.preparation_error));
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/*
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* We now have all sibling threads blocking and in "prepared" state in the
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* task work. Ask all threads to commit.
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* We now have either (a) all sibling threads blocking and in "prepared"
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* state in the task work, or (b) the preparation error is set. Ask all
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* threads to commit (or abort).
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*/
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complete_all(&shared_ctx.ready_to_commit);
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@ -556,6 +610,6 @@ int landlock_restrict_sibling_threads(const struct cred *old_cred,
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wait_for_completion(&shared_ctx.all_finished);
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tsync_works_release(&works);
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up_write(¤t->signal->exec_update_lock);
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return atomic_read(&shared_ctx.preparation_error);
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}
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@ -6,9 +6,10 @@
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*/
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#define _GNU_SOURCE
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#include <pthread.h>
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#include <sys/prctl.h>
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#include <linux/landlock.h>
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#include <pthread.h>
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#include <signal.h>
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#include <sys/prctl.h>
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#include "common.h"
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@ -158,4 +159,92 @@ TEST(competing_enablement)
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EXPECT_EQ(0, close(ruleset_fd));
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}
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static void signal_nop_handler(int sig)
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{
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}
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struct signaler_data {
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pthread_t target;
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volatile bool stop;
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};
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static void *signaler_thread(void *data)
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{
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struct signaler_data *sd = data;
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while (!sd->stop)
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pthread_kill(sd->target, SIGUSR1);
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return NULL;
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}
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/*
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* Number of idle sibling threads. This must be large enough that even on
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* machines with many cores, the sibling threads cannot all complete their
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* credential preparation in a single parallel wave, otherwise the signaler
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* thread has no window to interrupt wait_for_completion_interruptible().
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* 200 threads on a 64-core machine yields ~3 serialized waves, giving the
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* tight signal loop enough time to land an interruption.
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*/
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#define NUM_IDLE_THREADS 200
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/*
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* Exercises the tsync interruption and cancellation paths in tsync.c.
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*
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* When a signal interrupts the calling thread while it waits for sibling
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* threads to finish their credential preparation
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* (wait_for_completion_interruptible in landlock_restrict_sibling_threads),
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* the kernel sets ERESTARTNOINTR, cancels queued task works that have not
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* started yet (cancel_tsync_works), then waits for the remaining works to
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* finish. On the error return, syscalls.c aborts the prepared credentials.
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* The kernel automatically restarts the syscall, so userspace sees success.
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*/
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TEST(tsync_interrupt)
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{
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size_t i;
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pthread_t threads[NUM_IDLE_THREADS];
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pthread_t signaler;
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struct signaler_data sd;
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struct sigaction sa = {};
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const int ruleset_fd = create_ruleset(_metadata);
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disable_caps(_metadata);
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/* Install a no-op SIGUSR1 handler so the signal does not kill us. */
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sa.sa_handler = signal_nop_handler;
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sigemptyset(&sa.sa_mask);
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ASSERT_EQ(0, sigaction(SIGUSR1, &sa, NULL));
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ASSERT_EQ(0, prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0));
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for (i = 0; i < NUM_IDLE_THREADS; i++)
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ASSERT_EQ(0, pthread_create(&threads[i], NULL, idle, NULL));
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/*
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* Start a signaler thread that continuously sends SIGUSR1 to the
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* calling thread. This maximizes the chance of interrupting
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* wait_for_completion_interruptible() in the kernel's tsync path.
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*/
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sd.target = pthread_self();
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sd.stop = false;
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ASSERT_EQ(0, pthread_create(&signaler, NULL, signaler_thread, &sd));
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/*
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* The syscall may be interrupted and transparently restarted by the
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* kernel (ERESTARTNOINTR). From userspace, it should always succeed.
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*/
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EXPECT_EQ(0, landlock_restrict_self(ruleset_fd,
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LANDLOCK_RESTRICT_SELF_TSYNC));
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sd.stop = true;
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ASSERT_EQ(0, pthread_join(signaler, NULL));
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for (i = 0; i < NUM_IDLE_THREADS; i++) {
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ASSERT_EQ(0, pthread_cancel(threads[i]));
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ASSERT_EQ(0, pthread_join(threads[i], NULL));
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}
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EXPECT_EQ(0, close(ruleset_fd));
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}
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TEST_HARNESS_MAIN
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