Subject: CVE-2021-47080: RDMA/core: Prevent divide-by-zero error triggered by the user

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

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

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

RDMA/core: Prevent divide-by-zero error triggered by the user

The user_entry_size is supplied by the user and later used as a
denominator to calculate number of entries. The zero supplied by the user
will trigger the following divide-by-zero error:

 divide error: 0000 [#1] SMP KASAN PTI
 CPU: 4 PID: 497 Comm: c_repro Not tainted 5.13.0-rc1+ #281
 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
 RIP: 0010:ib_uverbs_handler_UVERBS_METHOD_QUERY_GID_TABLE+0x1b1/0x510
 Code: 87 59 03 00 00 e8 9f ab 1e ff 48 8d bd a8 00 00 00 e8 d3 70 41 ff 44 0f b7 b5 a8 00 00 00 e8 86 ab 1e ff 31 d2 4c 89 f0 31 ff <49> f7 f5 48 89 d6 48 89 54 24 10 48 89 04 24 e8 1b ad 1e ff 48 8b
 RSP: 0018:ffff88810416f828 EFLAGS: 00010246
 RAX: 0000000000000008 RBX: 1ffff1102082df09 RCX: ffffffff82183f3d
 RDX: 0000000000000000 RSI: ffff888105f2da00 RDI: 0000000000000000
 RBP: ffff88810416fa98 R08: 0000000000000001 R09: ffffed102082df5f
 R10: ffff88810416faf7 R11: ffffed102082df5e R12: 0000000000000000
 R13: 0000000000000000 R14: 0000000000000008 R15: ffff88810416faf0
 FS:  00007f5715efa740(0000) GS:ffff88811a700000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 0000000020000840 CR3: 000000010c2e0001 CR4: 0000000000370ea0
 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
 Call Trace:
  ? ib_uverbs_handler_UVERBS_METHOD_INFO_HANDLES+0x4b0/0x4b0
  ib_uverbs_cmd_verbs+0x1546/0x1940
  ib_uverbs_ioctl+0x186/0x240
  __x64_sys_ioctl+0x38a/0x1220
  do_syscall_64+0x3f/0x80
  entry_SYSCALL_64_after_hwframe+0x44/0xae

The Linux kernel CVE team has assigned CVE-2021-47080 to this issue.

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

	Issue introduced in 5.10 with commit 9f85cbe50aa0 and fixed in 5.10.40 with commit 66ab7fcdac34
	Issue introduced in 5.10 with commit 9f85cbe50aa0 and fixed in 5.12.7 with commit e6871b4270c0
	Issue introduced in 5.10 with commit 9f85cbe50aa0 and fixed in 5.13 with commit 54d87913f147

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-2021-47080
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/infiniband/core/uverbs_std_types_device.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/66ab7fcdac34b890017f04f391507ef5b2b89a13
	https://git.kernel.org/stable/c/e6871b4270c05f8b212e7d98aee82b357972c80a
	https://git.kernel.org/stable/c/54d87913f147a983589923c7f651f97de9af5be1