Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

xfrm: policy: fix metadata dst->dev xmit null pointer dereference

When we try to transmit an skb with metadata_dst attached (i.e. dst->dev == NULL) through xfrm interface we can hit a null pointer dereference[1] in xfrmi_xmit2() -> xfrm_lookup_with_ifid() due to the check for a loopback skb device when there's no policy which dereferences dst->dev unconditionally. Not having dst->dev can be interepreted as it not being a loopback device, so just add a check for a null dst_orig->dev.

With this fix xfrm interface's Tx error counters go up as usual.

[1] net-next calltrace captured via netconsole: BUG: kernel NULL pointer dereference, address: 00000000000000c0 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: 0000 [#1] PREEMPT SMP CPU: 1 PID: 7231 Comm: ping Kdump: loaded Not tainted 5.19.0+ #24 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.0-1.fc36 04/01/2014 RIP: 0010:xfrm_lookup_with_ifid+0x5eb/0xa60 Code: 8d 74 24 38 e8 26 a4 37 00 48 89 c1 e9 12 fc ff ff 49 63 ed 41 83 fd be 0f 85 be 01 00 00 41 be ff ff ff ff 45 31 ed 48 8b 03 <f6> 80 c0 00 00 00 08 75 0f 41 80 bc 24 19 0d 00 00 01 0f 84 1e 02 RSP: 0018:ffffb0db82c679f0 EFLAGS: 00010246 RAX: 0000000000000000 RBX: ffffd0db7fcad430 RCX: ffffb0db82c67a10 RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffb0db82c67a80 RBP: ffffb0db82c67a80 R08: ffffb0db82c67a1…