ksmbd: validate compound request size before reading StructureSize2

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[ Upstream commit 15b38176fd ]

When ksmbd validates a compound (chained) SMB2 request,
ksmbd_smb2_check_message() reads pdu->StructureSize2 without first
checking that the compound element is large enough to contain it.
StructureSize2 is a 2-byte field at offset 64
(__SMB2_HEADER_STRUCTURE_SIZE) from the start of each element.

The compound-walking logic only guarantees that a full 64-byte SMB2
header is present for the trailing element: when NextCommand is 0, len is
reduced to the number of bytes remaining after next_smb2_rcv_hdr_off. A
remote client can craft a compound request whose last element has exactly
64 bytes, so the 2-byte StructureSize2 read at offset 64 extends one byte
past the receive buffer, producing a slab-out-of-bounds read.

  BUG: KASAN: slab-out-of-bounds in ksmbd_smb2_check_message (fs/smb/server/smb2misc.c:402)
  Read of size 2 at addr ffff888012ae31ac by task kworker/0:1/14
  The buggy address is located 172 bytes inside of allocated 173-byte region
  Workqueue: ksmbd-io handle_ksmbd_work
  Call Trace:
   ...
   kasan_report (mm/kasan/report.c:595)
   ksmbd_smb2_check_message (fs/smb/server/smb2misc.c:402)
   handle_ksmbd_work (fs/smb/server/server.c:119)
   process_one_work (kernel/workqueue.c:3314)
   worker_thread (kernel/workqueue.c:3397)
   kthread (kernel/kthread.c:436)
   ret_from_fork (arch/x86/kernel/process.c:158)
   ret_from_fork_asm (arch/x86/entry/entry_64.S:245)

Reject any compound element that is too small to hold StructureSize2
before dereferencing it.

Fixes: e2f34481b2 ("cifsd: add server-side procedures for SMB3")
Reported-by: AutonomousCodeSecurity@microsoft.com
Signed-off-by: Xiang Mei (Microsoft) <xmei5@asu.edu>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

...

This commit is contained in:

Xiang Mei (Microsoft) 2026-07-13 21:55:10 +00:00 • committed by Greg Kroah-Hartman

parent 078ef8c95c

commit 415d0fff04

1 changed files with 5 additions and 0 deletions

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fs/ksmbd/smb2misc.c

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