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SubjectRe: [PATCH nf] netfilter: nfnetlink: correctly validate length of batch messages
On Tue, Feb 02, 2016 at 01:36:45PM -0500, phil.turnbull@oracle.com wrote:
> From: Phil Turnbull <phil.turnbull@oracle.com>
>
> If nlh->nlmsg_len is zero then an infinite loop is triggered because
> 'skb_pull(skb, msglen);' pulls zero bytes.
>
> The calculation in nlmsg_len() underflows if 'nlh->nlmsg_len <
> NLMSG_HDRLEN' which bypasses the length validation and will later
> trigger an out-of-bound read.
>
> If the length validation does fail then the malformed batch message is
> copied back to userspace. However, we cannot do this because the
> nlh->nlmsg_len can be invalid. This leads to an out-of-bounds read in
> netlink_ack:
>
> [ 41.455421] ==================================================================
> [ 41.456431] BUG: KASAN: slab-out-of-bounds in memcpy+0x1d/0x40 at addr ffff880119e79340
> [ 41.456431] Read of size 4294967280 by task a.out/987
> [ 41.456431] =============================================================================
> [ 41.456431] BUG kmalloc-512 (Not tainted): kasan: bad access detected
> [ 41.456431] -----------------------------------------------------------------------------
> ...
> [ 41.456431] Bytes b4 ffff880119e79310: 00 00 00 00 d5 03 00 00 b0 fb fe ff 00 00 00 00 ................
> [ 41.456431] Object ffff880119e79320: 20 00 00 00 10 00 05 00 00 00 00 00 00 00 00 00 ...............
> [ 41.456431] Object ffff880119e79330: 14 00 0a 00 01 03 fc 40 45 56 11 22 33 10 00 05 .......@EV."3...
> [ 41.456431] Object ffff880119e79340: f0 ff ff ff 88 99 aa bb 00 14 00 0a 00 06 fe fb ................
> ^^ start of batch nlmsg with
> nlmsg_len=4294967280
> ...
> [ 41.456431] Memory state around the buggy address:
> [ 41.456431] ffff880119e79400: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> [ 41.456431] ffff880119e79480: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> [ 41.456431] >ffff880119e79500: 00 00 00 00 fc fc fc fc fc fc fc fc fc fc fc fc
> [ 41.456431] ^
> [ 41.456431] ffff880119e79580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> [ 41.456431] ffff880119e79600: fc fc fc fc fc fc fc fc fc fc fb fb fb fb fb fb
> [ 41.456431] ==================================================================
>
> Fix this with better validation of nlh->nlmsg_len and by setting
> NFNL_BATCH_FAILURE if any batch message fails length validation.
>
> CAP_NET_ADMIN is required to trigger the bugs.

Applied, thanks.

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