diff options
| author | Eric Dumazet <edumazet@google.com> | 2018-10-10 06:59:35 -0700 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2018-10-10 10:21:31 -0700 |
| commit | 52b5d6f5dcf0e5201392f7d417148ccb537dbf6f (patch) | |
| tree | 68e2d7ca04a7aa0a13b0e7560489c003b87c0773 /net/core | |
| parent | 8b79f410438f5407ff45ceb72ad1eb02409652b4 (diff) | |
net: make skb_partial_csum_set() more robust against overflows
syzbot managed to crash in skb_checksum_help() [1] :
BUG_ON(offset + sizeof(__sum16) > skb_headlen(skb));
Root cause is the following check in skb_partial_csum_set()
if (unlikely(start > skb_headlen(skb)) ||
unlikely((int)start + off > skb_headlen(skb) - 2))
return false;
If skb_headlen(skb) is 1, then (skb_headlen(skb) - 2) becomes 0xffffffff
and the check fails to detect that ((int)start + off) is off the limit,
since the compare is unsigned.
When we fix that, then the first condition (start > skb_headlen(skb))
becomes obsolete.
Then we should also check that (skb_headroom(skb) + start) wont
overflow 16bit field.
[1]
kernel BUG at net/core/dev.c:2880!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 7330 Comm: syz-executor4 Not tainted 4.19.0-rc6+ #253
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:skb_checksum_help+0x9e3/0xbb0 net/core/dev.c:2880
Code: 85 00 ff ff ff 48 c1 e8 03 42 80 3c 28 00 0f 84 09 fb ff ff 48 8b bd 00 ff ff ff e8 97 a8 b9 fb e9 f8 fa ff ff e8 2d 09 76 fb <0f> 0b 48 8b bd 28 ff ff ff e8 1f a8 b9 fb e9 b1 f6 ff ff 48 89 cf
RSP: 0018:ffff8801d83a6f60 EFLAGS: 00010293
RAX: ffff8801b9834380 RBX: ffff8801b9f8d8c0 RCX: ffffffff8608c6d7
RDX: 0000000000000000 RSI: ffffffff8608cc63 RDI: 0000000000000006
RBP: ffff8801d83a7068 R08: ffff8801b9834380 R09: 0000000000000000
R10: ffff8801d83a76d8 R11: 0000000000000000 R12: 0000000000000001
R13: 0000000000010001 R14: 000000000000ffff R15: 00000000000000a8
FS: 00007f1a66db5700(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f7d77f091b0 CR3: 00000001ba252000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
skb_csum_hwoffload_help+0x8f/0xe0 net/core/dev.c:3269
validate_xmit_skb+0xa2a/0xf30 net/core/dev.c:3312
__dev_queue_xmit+0xc2f/0x3950 net/core/dev.c:3797
dev_queue_xmit+0x17/0x20 net/core/dev.c:3838
packet_snd net/packet/af_packet.c:2928 [inline]
packet_sendmsg+0x422d/0x64c0 net/packet/af_packet.c:2953
Fixes: 5ff8dda3035d ("net: Ensure partial checksum offset is inside the skb head")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/core')
| -rw-r--r-- | net/core/skbuff.c | 12 |
1 files changed, 7 insertions, 5 deletions
diff --git a/net/core/skbuff.c b/net/core/skbuff.c index b2c807f67aba..428094b577fc 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -4452,14 +4452,16 @@ EXPORT_SYMBOL_GPL(skb_complete_wifi_ack); */ bool skb_partial_csum_set(struct sk_buff *skb, u16 start, u16 off) { - if (unlikely(start > skb_headlen(skb)) || - unlikely((int)start + off > skb_headlen(skb) - 2)) { - net_warn_ratelimited("bad partial csum: csum=%u/%u len=%u\n", - start, off, skb_headlen(skb)); + u32 csum_end = (u32)start + (u32)off + sizeof(__sum16); + u32 csum_start = skb_headroom(skb) + (u32)start; + + if (unlikely(csum_start > U16_MAX || csum_end > skb_headlen(skb))) { + net_warn_ratelimited("bad partial csum: csum=%u/%u headroom=%u headlen=%u\n", + start, off, skb_headroom(skb), skb_headlen(skb)); return false; } skb->ip_summed = CHECKSUM_PARTIAL; - skb->csum_start = skb_headroom(skb) + start; + skb->csum_start = csum_start; skb->csum_offset = off; skb_set_transport_header(skb, start); return true; |