Re: [PATCH v1 net] af_packet: Don't cast tpacket_hdr.tp_len to int in tpacket_parse_header().

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

Kuniyuki Iwashima wrote:
> syzbot reported BUG() in sock_sendmsg_nosec(). [0]
> 
> The problem is that tpacket_parse_header() casts user-provided
> tpacket_hdr.tp_len, which is u32, to int.
> 
> If the length is larger than INT_MAX, the following condition
> in tpacket_parse_header() passes,
> 
>   if (unlikely(tp_len > size_max))
> 
> and any negative value can be returned to the caller, up to
> sock_sendmsg_nosec().
> 
> The repro set tpacket_hdr.tp_len to 0xfffffdef, which is cast
> to -EIOCBQUEUED (-529), triggering BUG() in sock_sendmsg_nosec().
> 
>   *(uint64_t*)0x200000000008 = 0xfffffdef;
>   ...
>   syscall(__NR_write, /*fd=*/r[0], /*buf=*/0x200000000000ul, /*count=*/1ul);
> 
> Let's define the local tp_len as u32 in tpacket_parse_header().
> 
> [0]:
> kernel BUG at net/socket.c:803!
> Oops: invalid opcode: 0000 [#1] SMP KASAN PTI
> CPU: 0 UID: 0 PID: 5628 Comm: syz-executor176 Not tainted syzkaller #0 PREEMPT(full)
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
> RIP: 0010:sock_sendmsg_nosec+0x145/0x180 net/socket.c:803
> Code: 06 67 48 0f b9 3a eb 95 e8 e8 3a 22 f8 48 89 df 4c 89 f6 4c 89 e2 4d 89 fb 2e e8 32 a5 5c 16 e9 51 ff ff ff e8 cc 3a 22 f8 90 <0f> 0b e8 c4 3a 22 f8 48 83 c3 18 48 89 d8 48 c1 e8 03 42 80 3c 28
> RSP: 0018:ffffc90003aefb48 EFLAGS: 00010293
> RAX: ffffffff89a578d4 RBX: ffff8880764c67c0 RCX: ffff88807fb23e80
> RDX: 0000000000000000 RSI: 00000000fffffdef RDI: 00000000fffffdef
> RBP: 00000000fffffdef R08: ffffc90003aef747 R09: 1ffff9200075dee8
> R10: dffffc0000000000 R11: fffff5200075dee9 R12: 0000000000000001
> R13: dffffc0000000000 R14: ffffc90003aefbc0 R15: ffffffff8aac4310
> FS:  000055559101b400(0000) GS:ffff888124ce0000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000200000000210 CR3: 0000000073dca000 CR4: 00000000003526f0
> Call Trace:
>  <TASK>
>  __sock_sendmsg net/socket.c:815 [inline]
>  sock_write_iter+0x2de/0x3e0 net/socket.c:1266
>  new_sync_write fs/read_write.c:595 [inline]
>  vfs_write+0x612/0xba0 fs/read_write.c:687
>  ksys_write+0x150/0x270 fs/read_write.c:739
>  do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
>  do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f173130ecb9
> Code: c0 79 93 eb d5 48 8d 7c 1d 00 eb 99 0f 1f 44 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 d8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007ffd67e44248 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> RAX: ffffffffffffffda RBX: 0000200000000000 RCX: 00007f173130ecb9
> RDX: 0000000000000001 RSI: 0000200000000000 RDI: 0000000000000003
> RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffd67e44388
> R13: 0000000000000002 R14: 00002000000000c0 R15: 0000000000000002
>  </TASK>
> 
> Fixes: 69e3c75f4d54 ("net: TX_RING and packet mmap")
> Reported-by: syzbot+73df3f89e1e13089e466@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/netdev/6a946ffa.1d9ded08.62e62.0123.GAE@google.com/
> Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>

Reviewed-by: Willem de Bruijn <willemb@google.com>