From d64cb81dcbd54927515a7f65e5e24affdc73c14b Mon Sep 17 00:00:00 2001 From: Yucheng Lu Date: Tue, 31 Mar 2026 16:00:21 +0800 Subject: [PATCH] net/sched: sch_netem: fix out-of-bounds access in packet corruption In netem_enqueue(), the packet corruption logic uses get_random_u32_below(skb_headlen(skb)) to select an index for modifying skb->data. When an AF_PACKET TX_RING sends fully non-linear packets over an IPIP tunnel, skb_headlen(skb) evaluates to 0. Passing 0 to get_random_u32_below() takes the variable-ceil slow path which returns an unconstrained 32-bit random integer. Using this unconstrained value as an offset into skb->data results in an out-of-bounds memory access. Fix this by verifying skb_headlen(skb) is non-zero before attempting to corrupt the linear data area. Fully non-linear packets will silently bypass the corruption logic. Fixes: c865e5d99e25 ("[PKT_SCHED] netem: packet corruption option") Reported-by: Yifan Wu Reported-by: Juefei Pu Signed-off-by: Yuan Tan Signed-off-by: Xin Liu Signed-off-by: Yuhang Zheng Signed-off-by: Yucheng Lu Reviewed-by: Stephen Hemminger Link: https://patch.msgid.link/45435c0935df877853a81e6d06205ac738ec65fa.1774941614.git.kanolyc@gmail.com Signed-off-by: Jakub Kicinski --- net/sched/sch_netem.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c index 5de1c932944a..20df1c08b1e9 100644 --- a/net/sched/sch_netem.c +++ b/net/sched/sch_netem.c @@ -519,8 +519,9 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch, goto finish_segs; } - skb->data[get_random_u32_below(skb_headlen(skb))] ^= - 1<data[get_random_u32_below(skb_headlen(skb))] ^= + 1 << get_random_u32_below(8); } if (unlikely(q->t_len >= sch->limit)) {