CVE-2026-89515: scsi: core: Fill in DMA padding bytes in scsi_alloc_sgtables()

CVE-2026-89515: scsi: core: Fill in DMA padding bytes in scsi_alloc_sgtables()

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

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

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

scsi: core: Fill in DMA padding bytes in scsi_alloc_sgtables()

During fuzz testing, the following issue was discovered:

BUG: KMSAN: uninit-value in __dma_map_sg_attrs+0x217/0x310
 __dma_map_sg_attrs+0x217/0x310
 dma_map_sg_attrs+0x4a/0x70
 ata_qc_issue+0x9f8/0x1420
 __ata_scsi_queuecmd+0x1657/0x1740
 ata_scsi_queuecmd+0x79a/0x920
 scsi_queue_rq+0x4472/0x4f40
 blk_mq_dispatch_rq_list+0x1cca/0x3ee0
 __blk_mq_sched_dispatch_requests+0x458/0x630
 blk_mq_sched_dispatch_requests+0x15b/0x340
 __blk_mq_run_hw_queue+0xe5/0x250
 __blk_mq_delay_run_hw_queue+0x138/0x780
 blk_mq_run_hw_queue+0x4bb/0x7e0
 blk_mq_sched_insert_request+0x2a7/0x4c0
 blk_execute_rq+0x497/0x8a0
 sg_io+0xbe0/0xe20
 scsi_ioctl+0x2b36/0x3c60
 sr_block_ioctl+0x319/0x440
 blkdev_ioctl+0x80f/0xd70
 __se_sys_ioctl+0x219/0x420
 __x64_sys_ioctl+0x93/0xe0
 x64_sys_call+0x1d6c/0x3ad0
 do_syscall_64+0x4c/0xa0
 entry_SYSCALL_64_after_hwframe+0x6e/0xd8

Uninit was created at:
 __alloc_pages+0x5c0/0xc80
 alloc_pages+0xe0e/0x1050
 blk_rq_map_user_iov+0x2b77/0x6100
 blk_rq_map_user_io+0x2fa/0x4d0
 sg_io+0xad6/0xe20
 scsi_ioctl+0x2b36/0x3c60
 sr_block_ioctl+0x319/0x440
 blkdev_ioctl+0x80f/0xd70
 __se_sys_ioctl+0x219/0x420
 __x64_sys_ioctl+0x93/0xe0
 x64_sys_call+0x1d6c/0x3ad0
 do_syscall_64+0x4c/0xa0
 entry_SYSCALL_64_after_hwframe+0x6e/0xd8

Bytes 14-15 of 16 are uninitialized
Memory access of size 16 starts at ffff88800cbdb000

When processing the last unaligned element of the scatterlist, it is
supplemented with missing bytes in the amount of pad_len.  These bytes
remain uninitialized, which leads to a problem.

Extend last_sg->length by pad_len first, then use sg_zero_buffer() to
zero those pad_len bytes.  sg_zero_buffer() uses sg_miter internally,
which correctly handles sg entries spanning multiple pages and padding
that crosses a page boundary.

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.

The Linux kernel CVE team has assigned CVE-2026-89515 to this issue.


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

	Issue introduced in 2.6.25 with commit 40b01b9bbdf51ae543a04744283bf2d56c4a6afa and fixed in 6.12.109 with commit a4353ec7742bdf87dcdde5875270feb3a1982a51
	Issue introduced in 2.6.25 with commit 40b01b9bbdf51ae543a04744283bf2d56c4a6afa and fixed in 6.18.50 with commit e7143c3f4e5c0a7986733c6f27009274bf6c4264
	Issue introduced in 2.6.25 with commit 40b01b9bbdf51ae543a04744283bf2d56c4a6afa and fixed in 7.2.4 with commit 6fd1cce5018fdcc8d928e00a6a1dd2997d5b9409
	Issue introduced in 2.6.25 with commit 40b01b9bbdf51ae543a04744283bf2d56c4a6afa and fixed in 7.3-rc1 with commit 626147717bea776b61ed3631d2c26283760c4cc4

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-2026-89515
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_lib.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/a4353ec7742bdf87dcdde5875270feb3a1982a51
	https://git.kernel.org/stable/c/e7143c3f4e5c0a7986733c6f27009274bf6c4264
	https://git.kernel.org/stable/c/6fd1cce5018fdcc8d928e00a6a1dd2997d5b9409
	https://git.kernel.org/stable/c/626147717bea776b61ed3631d2c26283760c4cc4