CVE-2026-64578ksmbd: validate compound request size before reading StructureSize2

Official description

In the Linux kernel, the following vulnerability has been resolved: ksmbd: validate compound request size before reading StructureSize2 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.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/415d0fff0451ad7ad4caa910f2bb0f562f0fd60f
• https://git.kernel.org/stable/c/1b6740525f5af90868d557c31b496ae689c8c549
• https://git.kernel.org/stable/c/2c307126ed8e7adddab82b8e31d962d3a2156ab1
• https://git.kernel.org/stable/c/f7550a91ab211726f59cb137523b7a9eae1ac6eb
• https://git.kernel.org/stable/c/f0e337e7db67cc1c832958bbb6c4026bdceacfdb
• https://git.kernel.org/stable/c/ea128f06d2fb2186f0cac0c9f3e953e4d1f5c29a
• https://git.kernel.org/stable/c/15b38176fd1530372905c602fde51fe89ec8c877