Fix an issue detected by syzbot: KMSAN reported an uninitialized-value access in sctp_inq_pop BUG: KMSAN: uninit-value in sctp_inq_pop The issue is actually caused by skb trimming via sk_filter() in sctp_rcv(). In the reproducer, skb->len becomes 1 after sk_filter(), which bypassed the original check: if (skb->len < sizeof(struct sctphdr) + sizeof(struct sctp_chunkhdr) + skb_transport_offset(skb)) To handle this safely, a new check should be performed after sk_filter(). Reported-by: syzbot+d101e12bccd4095460e7@syzkaller.appspotmail.com Tested-by: syzbot+d101e12bccd4095460e7@syzkaller.appspotmail.com Fixes: https://syzkaller.appspot.com/bug?extid=d101e12bccd4095460e7 Suggested-by: Xin Long Signed-off-by: Ranganath V N --- KMSAN reported an uninitialized-value access in sctp_inq_pop --- Changes in v2: - changes in commit message as per the code changes. - fixed as per the suggestion. - Link to v1: https://lore.kernel.org/r/20251023-kmsan_fix-v1-1-d08c18db8877@gmail.com --- net/sctp/input.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/sctp/input.c b/net/sctp/input.c index 7e99894778d4..e119e460ccde 100644 --- a/net/sctp/input.c +++ b/net/sctp/input.c @@ -190,7 +190,7 @@ int sctp_rcv(struct sk_buff *skb) goto discard_release; nf_reset_ct(skb); - if (sk_filter(sk, skb)) + if (sk_filter(sk, skb) || skb->len < sizeof(struct sctp_chunkhdr)) goto discard_release; /* Create an SCTP packet structure. */ --- base-commit: 43e9ad0c55a369ecc84a4788d06a8a6bfa634f1c change-id: 20251023-kmsan_fix-78d527b9960b Best regards, -- Ranganath V N