Subject: CVE-2021-46947: sfc: adjust efx->xdp_tx_queue_count with the real number of initialized queues

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

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

sfc: adjust efx->xdp_tx_queue_count with the real number of initialized queues

efx->xdp_tx_queue_count is initially initialized to num_possible_cpus() and is
later used to allocate and traverse efx->xdp_tx_queues lookup array. However,
we may end up not initializing all the array slots with real queues during
probing. This results, for example, in a NULL pointer dereference, when running
"# ethtool -S <iface>", similar to below

[2570283.664955][T4126959] BUG: kernel NULL pointer dereference, address: 00000000000000f8
[2570283.681283][T4126959] #PF: supervisor read access in kernel mode
[2570283.695678][T4126959] #PF: error_code(0x0000) - not-present page
[2570283.710013][T4126959] PGD 0 P4D 0
[2570283.721649][T4126959] Oops: 0000 [#1] SMP PTI
[2570283.734108][T4126959] CPU: 23 PID: 4126959 Comm: ethtool Tainted: G           O      5.10.20-cloudflare-2021.3.1 #1
[2570283.752641][T4126959] Hardware name: <redacted>
[2570283.781408][T4126959] RIP: 0010:efx_ethtool_get_stats+0x2ca/0x330 [sfc]
[2570283.796073][T4126959] Code: 00 85 c0 74 39 48 8b 95 a8 0f 00 00 48 85 d2 74 2d 31 c0 eb 07 48 8b 95 a8 0f 00 00 48 63 c8 49 83 c4 08 83 c0 01 48 8b 14 ca <48> 8b 92 f8 00 00 00 49 89 54 24 f8 39 85 a0 0f 00 00 77 d7 48 8b
[2570283.831259][T4126959] RSP: 0018:ffffb79a77657ce8 EFLAGS: 00010202
[2570283.845121][T4126959] RAX: 0000000000000019 RBX: ffffb799cd0c9280 RCX: 0000000000000018
[2570283.860872][T4126959] RDX: 0000000000000000 RSI: ffff96dd970ce000 RDI: 0000000000000005
[2570283.876525][T4126959] RBP: ffff96dd86f0a000 R08: ffff96dd970ce480 R09: 000000000000005f
[2570283.892014][T4126959] R10: ffffb799cd0c9fff R11: ffffb799cd0c9000 R12: ffffb799cd0c94f8
[2570283.907406][T4126959] R13: ffffffffc11b1090 R14: ffff96dd970ce000 R15: ffffffffc11cd66c
[2570283.922705][T4126959] FS:  00007fa7723f8740(0000) GS:ffff96f51fac0000(0000) knlGS:0000000000000000
[2570283.938848][T4126959] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[2570283.952524][T4126959] CR2: 00000000000000f8 CR3: 0000001a73e6e006 CR4: 00000000007706e0
[2570283.967529][T4126959] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[2570283.982400][T4126959] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[2570283.997308][T4126959] PKRU: 55555554
[2570284.007649][T4126959] Call Trace:
[2570284.017598][T4126959]  dev_ethtool+0x1832/0x2830

Fix this by adjusting efx->xdp_tx_queue_count after probing to reflect the true
value of initialized slots in efx->xdp_tx_queues.

The Linux kernel CVE team has assigned CVE-2021-46947 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 5.12 with commit e26ca4b53582 and fixed in 5.12.3 with commit ebeac958b690
	Issue introduced in 5.12 with commit e26ca4b53582 and fixed in 5.13 with commit 99ba0ea616aa

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2021-46947
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	drivers/net/ethernet/sfc/efx_channels.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/ebeac958b690123a0b40aa61f688f2f170035fad
	https://git.kernel.org/stable/c/99ba0ea616aabdc8e26259fd722503e012199a76