3.16.62-rc1 review patch. If anyone has any objections, please let me know.
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From: Eric Dumazet edumazet@google.com
commit 52b5d6f5dcf0e5201392f7d417148ccb537dbf6f upstream.
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 Signed-off-by: Ben Hutchings ben@decadent.org.uk --- net/core/skbuff.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-)
--- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -3593,14 +3593,16 @@ 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;