On Tue, Feb 02, 2016 at 01:36:45PM -0500, phil.turnbull@xxxxxxxxxx wrote: > From: Phil Turnbull <phil.turnbull@xxxxxxxxxx> > > 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. -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
