Affected: Linux

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

xsk: check IFF_UP earlier in Tx path

Xsk Tx can be triggered via either sendmsg() or poll() syscalls. These two paths share a call to common function xsk_xmit() which has two sanity checks within. A pseudo code example to show the two paths:

__xsk_sendmsg() : xsk_poll(): if (unlikely(!xsk_is_bound(xs))) if (unlikely(!xsk_is_bound(xs))) return -ENXIO; return mask; if (unlikely(need_wait)) (...) return -EOPNOTSUPP; xsk_xmit() mark napi id (...) xsk_xmit()

xsk_xmit(): if (unlikely(!(xs->dev->flags & IFF_UP))) return -ENETDOWN; if (unlikely(!xs->tx)) return -ENOBUFS;

As it can be observed above, in sendmsg() napi id can be marked on interface that was not brought up and this causes a NULL ptr dereference:

[31757.505631] BUG: kernel NULL pointer dereference, address: 0000000000000018 [31757.512710] #PF: supervisor read access in kernel mode [31757.517936] #PF: error_code(0x0000) - not-present page [31757.523149] PGD 0 P4D 0 [31757.525726] Oops: 0000 [#1] PREEMPT SMP NOPTI [31757.530154] CPU: 26 PID: 95641 Comm: xdpsock Not tainted 6.2.0-rc5+ #40 [31757.536871] Hardware name: Intel Corporation S2600WFT/S2600WFT, BIOS SE5C620.86B.02.01.0008.031920191559 03/19/2019 [31757.547457] RIP: 0010:xsk_sendmsg+0xde/0x180 [31757.551799] Code: 00 75 a2 48 8b 00 a8 04 75 9b 84 d2 74 69 8b 85 14 01 00 00 85 c0 75 1b 48 8b 85 28 0…