net: sctp: fix KMSAN uninit-value in sctp_inq_pop

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
Closes: https://syzkaller.appspot.com/bug?extid=d101e12bccd4095460e7
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Suggested-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: Ranganath V N <vnranganath.20@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20251026-kmsan_fix-v3-1-2634a409fa5f@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/net/sctp/input.c b/net/sctp/input.c
index 7e99894778d4fd3bf4d243c6108d04cc82498eab..e119e460ccde0b8ac68e10ca2cb1f1c2c5e9cccf 100644 (file)
--- 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. */