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authorEric Dumazet <edumazet@google.com>2018-10-10 15:59:35 +0200
committerDavid S. Miller <davem@davemloft.net>2018-10-10 19:21:31 +0200
commit52b5d6f5dcf0e5201392f7d417148ccb537dbf6f (patch)
tree68e2d7ca04a7aa0a13b0e7560489c003b87c0773
parentMerge branch 'devlink-param-type-string-fixes' (diff)
downloadlinux-52b5d6f5dcf0e5201392f7d417148ccb537dbf6f.tar.xz
linux-52b5d6f5dcf0e5201392f7d417148ccb537dbf6f.zip
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>
-rw-r--r--net/core/skbuff.c12
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;