Re: [syzbot] kernel BUG in ip_frag_next

[Jesper Dangaard Brouer <jbrouer@redhat.com>]

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On 18/01/2023 17.52, syzbot wrote:
> Hello,

Hi Syzbot,

Could you test this attached patch please, against:

#syz test git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git
master


> syzbot found the following issue on:
> 
> HEAD commit:    0c68c8e5ec68 net: mdio: cavium: Remove unneeded simicolons
> git tree:       net-next
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=147c7051480000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=4695869845c5f393
> dashboard link: https://syzkaller.appspot.com/bug?extid=c8a2e66e37eee553c4fd
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=173fca39480000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=107ba0a9480000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/15c191498614/disk-0c68c8e5.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/7c4c9368d89c/vmlinux-0c68c8e5.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/083770efc7c4/bzImage-0c68c8e5.xz
> 
> The issue was bisected to:
> 
> commit eedade12f4cb7284555c4c0314485e9575c70ab7
> Author: Jesper Dangaard Brouer <brouer@redhat.com>
> Date:   Fri Jan 13 13:52:04 2023 +0000
> 
>      net: kfree_skb_list use kmem_cache_free_bulk
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1136ec41480000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=1336ec41480000
> console output: https://syzkaller.appspot.com/x/log.txt?x=1536ec41480000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+c8a2e66e37eee553c4fd@syzkaller.appspotmail.com
> Fixes: eedade12f4cb ("net: kfree_skb_list use kmem_cache_free_bulk")
> 
> raw_sendmsg: syz-executor409 forgot to set AF_INET. Fix it!
> ------------[ cut here ]------------
> kernel BUG at net/ipv4/ip_output.c:724!
> invalid opcode: 0000 [#1] PREEMPT SMP KASAN
> CPU: 1 PID: 5073 Comm: syz-executor409 Not tainted 6.2.0-rc3-syzkaller-00457-g0c68c8e5ec68 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/12/2023
> RIP: 0010:ip_frag_next+0xa03/0xa50 net/ipv4/ip_output.c:724
> Code: e8 82 b1 86 f9 e9 95 fa ff ff 48 8b 3c 24 e8 74 b1 86 f9 e9 5b f8 ff ff 4c 89 ff e8 67 b1 86 f9 e9 1f f8 ff ff e8 3d ad 38 f9 <0f> 0b 48 89 54 24 20 4c 89 44 24 18 e8 4c b1 86 f9 48 8b 54 24 20
> RSP: 0018:ffffc90003a6f6b8 EFLAGS: 00010293
> RAX: 0000000000000000 RBX: ffffc90003a6f818 RCX: 0000000000000000
> RDX: ffff8880772c0000 RSI: ffffffff8848a583 RDI: 0000000000000005
> RBP: 00000000000005c8 R08: 0000000000000005 R09: 0000000000000000
> R10: 00000000fffffff2 R11: 0000000000000000 R12: ffff888026841dc0
> R13: ffffc90003a6f81c R14: 00000000fffffff2 R15: ffffc90003a6f830
> FS:  0000555555b08300(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00005622b70166a8 CR3: 000000007780f000 CR4: 00000000003506e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>   <TASK>
>   ip_do_fragment+0x873/0x17d0 net/ipv4/ip_output.c:902
>   ip_fragment.constprop.0+0x16b/0x240 net/ipv4/ip_output.c:581
>   __ip_finish_output net/ipv4/ip_output.c:304 [inline]
>   __ip_finish_output+0x2de/0x650 net/ipv4/ip_output.c:288
>   ip_finish_output+0x31/0x280 net/ipv4/ip_output.c:316
>   NF_HOOK_COND include/linux/netfilter.h:291 [inline]
>   ip_mc_output+0x21f/0x710 net/ipv4/ip_output.c:415
>   dst_output include/net/dst.h:444 [inline]
>   ip_local_out net/ipv4/ip_output.c:126 [inline]
>   ip_send_skb net/ipv4/ip_output.c:1586 [inline]
>   ip_push_pending_frames+0x129/0x2b0 net/ipv4/ip_output.c:1606
>   raw_sendmsg+0x1338/0x2df0 net/ipv4/raw.c:645
>   inet_sendmsg+0x9d/0xe0 net/ipv4/af_inet.c:827
>   sock_sendmsg_nosec net/socket.c:722 [inline]
>   sock_sendmsg+0xde/0x190 net/socket.c:745
>   __sys_sendto+0x23a/0x340 net/socket.c:2142
>   __do_sys_sendto net/socket.c:2154 [inline]
>   __se_sys_sendto net/socket.c:2150 [inline]
>   __x64_sys_sendto+0xe1/0x1b0 net/socket.c:2150
>   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>   do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
>   entry_SYSCALL_64_after_hwframe+0x63/0xcd
> RIP: 0033:0x7f8efa22c499
> Code: 28 c3 e8 4a 15 00 00 66 2e 0f 1f 84 00 00 00 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007ffd43ed3198 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
> RAX: ffffffffffffffda RBX: 00007ffd43ed31b8 RCX: 00007f8efa22c499
> RDX: 000000000000fcf2 RSI: 0000000020000380 RDI: 0000000000000003
> RBP: 0000000000000003 R08: 0000000020001380 R09: 000000000000006e
> R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffd43ed31c0
> R13: 00007ffd43ed31e0 R14: 0000000000000000 R15: 0000000000000000
>   </TASK>
> Modules linked in:
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:ip_frag_next+0xa03/0xa50 net/ipv4/ip_output.c:724
> Code: e8 82 b1 86 f9 e9 95 fa ff ff 48 8b 3c 24 e8 74 b1 86 f9 e9 5b f8 ff ff 4c 89 ff e8 67 b1 86 f9 e9 1f f8 ff ff e8 3d ad 38 f9 <0f> 0b 48 89 54 24 20 4c 89 44 24 18 e8 4c b1 86 f9 48 8b 54 24 20
> RSP: 0018:ffffc90003a6f6b8 EFLAGS: 00010293
> RAX: 0000000000000000 RBX: ffffc90003a6f818 RCX: 0000000000000000
> RDX: ffff8880772c0000 RSI: ffffffff8848a583 RDI: 0000000000000005
> RBP: 00000000000005c8 R08: 0000000000000005 R09: 0000000000000000
> R10: 00000000fffffff2 R11: 0000000000000000 R12: ffff888026841dc0
> R13: ffffc90003a6f81c R14: 00000000fffffff2 R15: ffffc90003a6f830
> FS:  0000555555b08300(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000557162e92068 CR3: 000000007780f000 CR4: 00000000003506e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> 
> 
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@googlegroups.com.
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> syzbot can test patches for this issue, for details see:
> https://goo.gl/tpsmEJ#testing-patches
> 

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net: fix kfree_skb_list use of skb_mark_not_on_list

From: Jesper Dangaard Brouer <brouer@redhat.com>

A bug was introduced by commit eedade12f4cb ("net: kfree_skb_list use
kmem_cache_free_bulk"). It unconditionally unlinked the SKB list via
invoking skb_mark_not_on_list().

The skb_mark_not_on_list() should only be called if __kfree_skb_reason()
returns true, meaning the SKB is ready to be free'ed (as it calls/check
skb_unref()).

Reported-by: syzbot+c8a2e66e37eee553c4fd@syzkaller.appspotmail.com
Fixes: eedade12f4cb ("net: kfree_skb_list use kmem_cache_free_bulk")
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
---
 net/core/skbuff.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 4e73ab3482b8..1bffbcbe6087 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -999,10 +999,10 @@ kfree_skb_list_reason(struct sk_buff *segs, enum skb_drop_reason reason)
 	while (segs) {
 		struct sk_buff *next = segs->next;
 
-		skb_mark_not_on_list(segs);
-
-		if (__kfree_skb_reason(segs, reason))
+		if (__kfree_skb_reason(segs, reason)) {
+			skb_mark_not_on_list(segs);
 			kfree_skb_add_bulk(segs, &sa, reason);
+		}
 
 		segs = next;
 	}