Re: [syzbot] general protection fault in nft_set_elem_expr_alloc

Hi Pablo,

On Wed, Jun 02, 2021 at 07:03:17PM +0200, Pablo Neira Ayuso wrote:

On Wed, Jun 02, 2021 at 09:37:26AM -0700, syzbot wrote:

quoted

Hello,

syzbot found the following issue on:

HEAD commit:    6850ec97 Merge branch 'mptcp-fixes-for-5-13'
git tree:       net
console output: https://syzkaller.appspot.com/x/log.txt?x=1355504dd00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=770708ea7cfd4916
dashboard link: https://syzkaller.appspot.com/bug?extid=ce96ca2b1d0b37c6422d
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1502d517d00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12bbbe13d00000

The issue was bisected to:

commit 05abe4456fa376040f6cc3cc6830d2e328723478
Author: Pablo Neira Ayuso [off-list ref]
Date:   Wed May 20 13:44:37 2020 +0000

    netfilter: nf_tables: allow to register flowtable with no devices

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=10fa1387d00000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=12fa1387d00000
console output: https://syzkaller.appspot.com/x/log.txt?x=14fa1387d00000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ce96ca2b1d0b37c6422d@syzkaller.appspotmail.com
Fixes: 05abe4456fa3 ("netfilter: nf_tables: allow to register flowtable with no devices")

general protection fault, probably for non-canonical address 0xdffffc000000000e: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000070-0x0000000000000077]
CPU: 1 PID: 8438 Comm: syz-executor343 Not tainted 5.13.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:nft_set_elem_expr_alloc+0x17e/0x280 net/netfilter/nf_tables_api.c:5321
Code: 48 c1 ea 03 80 3c 02 00 0f 85 09 01 00 00 49 8b 9d c0 00 00 00 48 b8 00 00 00 00 00 fc ff df 48 8d 7b 70 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 d9 00 00 00 48 8b 5b 70 48 85 db 74 21 e8 9a bd

It's a real bug. Bisect is not correct though.

I'll post a patch to fix it. Thanks.

So if I see it correctly the fix landed in ad9f151e560b ("netfilter:
nf_tables: initialize set before expression setup") in 5.13-rc7 and
landed as well in 5.12.13. The issue is though still present in the
5.10.y series.

Would it be possible to backport the fix as well to 5.10.y? It is
needed there as well.

Regards,
Salvatore