Re: net/ipv6: slab-out-of-bounds read in seg6_validate_srh

[David Lebrun]

On 04/18/2017 04:54 PM, Andrey Konovalov wrote:
> Hi,
> 
> I've got the following error report while fuzzing the kernel with syzkaller.
> 
> On commit 4f7d029b9bf009fbee76bb10c0c4351a1870d2f3 (4.11-rc7).
> 
> A reproducer and .config are attached.
> 
> ==================================================================
> BUG: KASAN: slab-out-of-bounds in seg6_validate_srh+0x203/0x220
> net/ipv6/seg6.c:57 at addr ffff88006a759608
> Read of size 1 by task syz-executor4/2627

Thanks for the report. It seems to happen when the trailing data is less
than sizeof(struct sr6_tlv). The following (untested) patch should fix
the issue, I'll test it and submit it properly if it works.

diff --git a/net/ipv6/seg6.c b/net/ipv6/seg6.c
index a855eb3..5f44ffe 100644
--- a/net/ipv6/seg6.c
+++ b/net/ipv6/seg6.c
@@ -53,6 +53,9 @@ bool seg6_validate_srh(struct ipv6_sr_hdr *srh, int len)
 		struct sr6_tlv *tlv;	
 		unsigned int tlv_len;

+		if (trailing < sizeof(*tlv))
+			return false;
+
 		tlv = (struct sr6_tlv *)((unsigned char *)srh + tlv_offset);
 		tlv_len = sizeof(*tlv) + tlv->len;

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