Subject: CVE-2021-47191: scsi: scsi_debug: Fix out-of-bound read in resp_readcap16()

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

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

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

scsi: scsi_debug: Fix out-of-bound read in resp_readcap16()

The following warning was observed running syzkaller:

[ 3813.830724] sg_write: data in/out 65466/242 bytes for SCSI command 0x9e-- guessing data in;
[ 3813.830724]    program syz-executor not setting count and/or reply_len properly
[ 3813.836956] ==================================================================
[ 3813.839465] BUG: KASAN: stack-out-of-bounds in sg_copy_buffer+0x157/0x1e0
[ 3813.841773] Read of size 4096 at addr ffff8883cf80f540 by task syz-executor/1549
[ 3813.846612] Call Trace:
[ 3813.846995]  dump_stack+0x108/0x15f
[ 3813.847524]  print_address_description+0xa5/0x372
[ 3813.848243]  kasan_report.cold+0x236/0x2a8
[ 3813.849439]  check_memory_region+0x240/0x270
[ 3813.850094]  memcpy+0x30/0x80
[ 3813.850553]  sg_copy_buffer+0x157/0x1e0
[ 3813.853032]  sg_copy_from_buffer+0x13/0x20
[ 3813.853660]  fill_from_dev_buffer+0x135/0x370
[ 3813.854329]  resp_readcap16+0x1ac/0x280
[ 3813.856917]  schedule_resp+0x41f/0x1630
[ 3813.858203]  scsi_debug_queuecommand+0xb32/0x17e0
[ 3813.862699]  scsi_dispatch_cmd+0x330/0x950
[ 3813.863329]  scsi_request_fn+0xd8e/0x1710
[ 3813.863946]  __blk_run_queue+0x10b/0x230
[ 3813.864544]  blk_execute_rq_nowait+0x1d8/0x400
[ 3813.865220]  sg_common_write.isra.0+0xe61/0x2420
[ 3813.871637]  sg_write+0x6c8/0xef0
[ 3813.878853]  __vfs_write+0xe4/0x800
[ 3813.883487]  vfs_write+0x17b/0x530
[ 3813.884008]  ksys_write+0x103/0x270
[ 3813.886268]  __x64_sys_write+0x77/0xc0
[ 3813.886841]  do_syscall_64+0x106/0x360
[ 3813.887415]  entry_SYSCALL_64_after_hwframe+0x44/0xa9

This issue can be reproduced with the following syzkaller log:

r0 = openat(0xffffffffffffff9c, &(0x7f0000000040)='./file0\x00', 0x26e1, 0x0)
r1 = syz_open_procfs(0xffffffffffffffff, &(0x7f0000000000)='fd/3\x00')
open_by_handle_at(r1, &(0x7f00000003c0)=ANY=[@ANYRESHEX], 0x602000)
r2 = syz_open_dev$sg(&(0x7f0000000000), 0x0, 0x40782)
write$binfmt_aout(r2, &(0x7f0000000340)=ANY=[@ANYBLOB="00000000deff000000000000000000000000000000000000000000000000000047f007af9e107a41ec395f1bded7be24277a1501ff6196a83366f4e6362bc0ff2b247f68a972989b094b2da4fb3607fcf611a22dd04310d28c75039d"], 0x126)

In resp_readcap16() we get "int alloc_len" value -1104926854, and then pass
the huge arr_len to fill_from_dev_buffer(), but arr is only 32 bytes. This
leads to OOB in sg_copy_buffer().

To solve this issue, define alloc_len as u32.

The Linux kernel CVE team has assigned CVE-2021-47191 to this issue.

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

	Fixed in 5.10.82 with commit 3e20cb072679
	Fixed in 5.15.5 with commit 5b8bed6464ad
	Fixed in 5.16 with commit 4e3ace0051e7

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-2021-47191
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/scsi/scsi_debug.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/3e20cb072679bdb47747ccc8bee3233a4cf0765a
	https://git.kernel.org/stable/c/5b8bed6464ad6653586e30df046185fd816ad999
	https://git.kernel.org/stable/c/4e3ace0051e7e504b55d239daab8789dd89b863c