Subject: CVE-2021-47563: ice: avoid bpf_prog refcount underflow

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

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

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

ice: avoid bpf_prog refcount underflow

Ice driver has the routines for managing XDP resources that are shared
between ndo_bpf op and VSI rebuild flow. The latter takes place for
example when user changes queue count on an interface via ethtool's
set_channels().

There is an issue around the bpf_prog refcounting when VSI is being
rebuilt - since ice_prepare_xdp_rings() is called with vsi->xdp_prog as
an argument that is used later on by ice_vsi_assign_bpf_prog(), same
bpf_prog pointers are swapped with each other. Then it is also
interpreted as an 'old_prog' which in turn causes us to call
bpf_prog_put on it that will decrement its refcount.

Below splat can be interpreted in a way that due to zero refcount of a
bpf_prog it is wiped out from the system while kernel still tries to
refer to it:

[  481.069429] BUG: unable to handle page fault for address: ffffc9000640f038
[  481.077390] #PF: supervisor read access in kernel mode
[  481.083335] #PF: error_code(0x0000) - not-present page
[  481.089276] PGD 100000067 P4D 100000067 PUD 1001cb067 PMD 106d2b067 PTE 0
[  481.097141] Oops: 0000 [#1] PREEMPT SMP PTI
[  481.101980] CPU: 12 PID: 3339 Comm: sudo Tainted: G           OE     5.15.0-rc5+ #1
[  481.110840] Hardware name: Intel Corp. GRANTLEY/GRANTLEY, BIOS GRRFCRB1.86B.0276.D07.1605190235 05/19/2016
[  481.122021] RIP: 0010:dev_xdp_prog_id+0x25/0x40
[  481.127265] Code: 80 00 00 00 00 0f 1f 44 00 00 89 f6 48 c1 e6 04 48 01 fe 48 8b 86 98 08 00 00 48 85 c0 74 13 48 8b 50 18 31 c0 48 85 d2 74 07 <48> 8b 42 38 8b 40 20 c3 48 8b 96 90 08 00 00 eb e8 66 2e 0f 1f 84
[  481.148991] RSP: 0018:ffffc90007b63868 EFLAGS: 00010286
[  481.155034] RAX: 0000000000000000 RBX: ffff889080824000 RCX: 0000000000000000
[  481.163278] RDX: ffffc9000640f000 RSI: ffff889080824010 RDI: ffff889080824000
[  481.171527] RBP: ffff888107af7d00 R08: 0000000000000000 R09: ffff88810db5f6e0
[  481.179776] R10: 0000000000000000 R11: ffff8890885b9988 R12: ffff88810db5f4bc
[  481.188026] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
[  481.196276] FS:  00007f5466d5bec0(0000) GS:ffff88903fb00000(0000) knlGS:0000000000000000
[  481.205633] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  481.212279] CR2: ffffc9000640f038 CR3: 000000014429c006 CR4: 00000000003706e0
[  481.220530] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  481.228771] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  481.237029] Call Trace:
[  481.239856]  rtnl_fill_ifinfo+0x768/0x12e0
[  481.244602]  rtnl_dump_ifinfo+0x525/0x650
[  481.249246]  ? __alloc_skb+0xa5/0x280
[  481.253484]  netlink_dump+0x168/0x3c0
[  481.257725]  netlink_recvmsg+0x21e/0x3e0
[  481.262263]  ____sys_recvmsg+0x87/0x170
[  481.266707]  ? __might_fault+0x20/0x30
[  481.271046]  ? _copy_from_user+0x66/0xa0
[  481.275591]  ? iovec_from_user+0xf6/0x1c0
[  481.280226]  ___sys_recvmsg+0x82/0x100
[  481.284566]  ? sock_sendmsg+0x5e/0x60
[  481.288791]  ? __sys_sendto+0xee/0x150
[  481.293129]  __sys_recvmsg+0x56/0xa0
[  481.297267]  do_syscall_64+0x3b/0xc0
[  481.301395]  entry_SYSCALL_64_after_hwframe+0x44/0xae
[  481.307238] RIP: 0033:0x7f5466f39617
[  481.311373] Code: 0c 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb bd 0f 1f 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 2f 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 51 c3 48 83 ec 28 89 54 24 1c 48 89 74 24 10
[  481.342944] RSP: 002b:00007ffedc7f4308 EFLAGS: 00000246 ORIG_RAX: 000000000000002f
[  481.361783] RAX: ffffffffffffffda RBX: 00007ffedc7f5460 RCX: 00007f5466f39617
[  481.380278] RDX: 0000000000000000 RSI: 00007ffedc7f5360 RDI: 0000000000000003
[  481.398500] RBP: 00007ffedc7f53f0 R08: 0000000000000000 R09: 000055d556f04d50
[  481.416463] R10: 0000000000000077 R11: 0000000000000246 R12: 00007ffedc7f5360
[  481.434131] R13: 00007ffedc7f5350 R14: 00007ffedc7f5344 R15: 0000000000000e98
[  481.451520] Modules linked in: ice(OE) af_packet binfmt_misc nls_iso8859_1 ipmi_ssif intel_rapl_msr intel_rapl_common x86_pkg_temp_thermal intel_powerclamp mxm_wmi mei_me coretemp mei ipmi_si ipmi_msghandler wmi acpi_pad acpi_power_meter ip_tables x_tables autofs4 crct10dif_pclmul crc32_pclmul ghash_clmulni_intel aesni_intel ahci crypto_simd cryptd libahci lpc_ich [last unloaded: ice]
[  481.528558] CR2: ffffc9000640f038
[  481.542041] ---[ end trace d1f24c9ecf5b61c1 ]---

Fix this by only calling ice_vsi_assign_bpf_prog() inside
ice_prepare_xdp_rings() when current vsi->xdp_prog pointer is NULL.
This way set_channels() flow will not attempt to swap the vsi->xdp_prog
pointers with itself.

Also, sprinkle around some comments that provide a reasoning about
correlation between driver and kernel in terms of bpf_prog refcount.

The Linux kernel CVE team has assigned CVE-2021-47563 to this issue.

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

	Issue introduced in 5.5 with commit efc2214b6047 and fixed in 5.10.83 with commit e65a8707b4cd
	Issue introduced in 5.5 with commit efc2214b6047 and fixed in 5.15.6 with commit 1f10b09ccc83
	Issue introduced in 5.5 with commit efc2214b6047 and fixed in 5.16 with commit f65ee535df77

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-2021-47563
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/intel/ice/ice_main.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/e65a8707b4cd756d26d246bb2b9fab06eebafac1
	https://git.kernel.org/stable/c/1f10b09ccc832698ef4624a6ab9a213b6ccbda76
	https://git.kernel.org/stable/c/f65ee535df775a13a1046c0a0b2d72db342f8a5b