On Tue, Sep 21, 2021 at 12:09 PM syzbot
[off-list ref] wrote:

quoted

Hello,

syzbot found the following issue on:

HEAD commit:    98dc68f8b0c2 selftests: nci: replace unsigned int with int
git tree:       net
console output: https://syzkaller.appspot.com/x/log.txt?x=11fd443d300000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c31c0936547df9ea
dashboard link: https://syzkaller.appspot.com/bug?extid=581aff2ae6b860625116
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+581aff2ae6b860625116@syzkaller.appspotmail.com

general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
CPU: 0 PID: 11205 Comm: kworker/0:12 Not tainted 5.14.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: ipv6_addrconf addrconf_dad_work
RIP: 0010:sctp_rcv_ootb net/sctp/input.c:705 [inline]

by anyway, checking if skb_header_pointer() return NULL is always needed:

@@ -702,7 +702,7 @@ static int sctp_rcv_ootb(struct sk_buff *skb)
                ch = skb_header_pointer(skb, offset, sizeof(*ch), &_ch);

                /* Break out if chunk length is less then minimal. */
-               if (ntohs(ch->length) < sizeof(_ch))
+               if (!ch || ntohs(ch->length) < sizeof(_ch))
                        break;