Subject: CVE-2021-47219: scsi: scsi_debug: Fix out-of-bound read in resp_report_tgtpgs()

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_report_tgtpgs()

The following issue was observed running syzkaller:

BUG: KASAN: slab-out-of-bounds in memcpy include/linux/string.h:377 [inline]
BUG: KASAN: slab-out-of-bounds in sg_copy_buffer+0x150/0x1c0 lib/scatterlist.c:831
Read of size 2132 at addr ffff8880aea95dc8 by task syz-executor.0/9815

CPU: 0 PID: 9815 Comm: syz-executor.0 Not tainted 4.19.202-00874-gfc0fe04215a9 #2
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0xe4/0x14a lib/dump_stack.c:118
 print_address_description+0x73/0x280 mm/kasan/report.c:253
 kasan_report_error mm/kasan/report.c:352 [inline]
 kasan_report+0x272/0x370 mm/kasan/report.c:410
 memcpy+0x1f/0x50 mm/kasan/kasan.c:302
 memcpy include/linux/string.h:377 [inline]
 sg_copy_buffer+0x150/0x1c0 lib/scatterlist.c:831
 fill_from_dev_buffer+0x14f/0x340 drivers/scsi/scsi_debug.c:1021
 resp_report_tgtpgs+0x5aa/0x770 drivers/scsi/scsi_debug.c:1772
 schedule_resp+0x464/0x12f0 drivers/scsi/scsi_debug.c:4429
 scsi_debug_queuecommand+0x467/0x1390 drivers/scsi/scsi_debug.c:5835
 scsi_dispatch_cmd+0x3fc/0x9b0 drivers/scsi/scsi_lib.c:1896
 scsi_request_fn+0x1042/0x1810 drivers/scsi/scsi_lib.c:2034
 __blk_run_queue_uncond block/blk-core.c:464 [inline]
 __blk_run_queue+0x1a4/0x380 block/blk-core.c:484
 blk_execute_rq_nowait+0x1c2/0x2d0 block/blk-exec.c:78
 sg_common_write.isra.19+0xd74/0x1dc0 drivers/scsi/sg.c:847
 sg_write.part.23+0x6e0/0xd00 drivers/scsi/sg.c:716
 sg_write+0x64/0xa0 drivers/scsi/sg.c:622
 __vfs_write+0xed/0x690 fs/read_write.c:485
kill_bdev:block_device:00000000e138492c
 vfs_write+0x184/0x4c0 fs/read_write.c:549
 ksys_write+0x107/0x240 fs/read_write.c:599
 do_syscall_64+0xc2/0x560 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

We get 'alen' from command its type is int. If userspace passes a large
length we will get a negative 'alen'.

Switch n, alen, and rlen to u32.

The Linux kernel CVE team has assigned CVE-2021-47219 to this issue.

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

	Fixed in 5.10.82 with commit 8440377e1a56
	Fixed in 5.15.5 with commit 66523553fa62
	Fixed in 5.16 with commit f347c26836c2

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-2021-47219
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/8440377e1a5644779b4c8d013aa2a917f5fc83c3
	https://git.kernel.org/stable/c/66523553fa62c7878fc5441dc4e82be71934eb77
	https://git.kernel.org/stable/c/f347c26836c270199de1599c3cd466bb7747caa9