Description

In the Linux kernel, the following vulnerability has been resolved: smb: server: fix active_num_conn leak on transport allocation failure Commit 77ffbcac4e56 ("smb: server: fix leak of active_num_conn in ksmbd_tcp_new_connection()") addressed the kthread_run() failure path. The earlier alloc_transport() == NULL path in the same function has the same leak, is reachable pre-authentication via any TCP connect to port 445, and was empirically reproduced on UML (ARCH=um, v7.0-rc7): a small number of forced allocation failures were sufficient to put ksmbd into a state where every subsequent connection attempt was rejected for the remainder of the boot. ksmbd_kthread_fn() increments active_num_conn before calling ksmbd_tcp_new_connection() and discards the return value, so when alloc_transport() returns NULL the socket is released and -ENOMEM returned without decrementing the counter. Each such failure permanently consumes one slot from the max_connections pool; once cumulative failures reach the cap, atomic_inc_return() hits the threshold on every subsequent accept and every new connection is rejected. The counter is only reset by module reload. An unauthenticated remote attacker can drive the server toward the memory pressure that makes alloc_transport() fail by holding open connections with large RFC1002 lengths up to MAX_STREAM_PROT_LEN (0x00FFFFFF); natural transient allocation failures on a loaded host produce the same drift more slowly. Mirror the existing rollback pattern in ksmbd_kthread_fn(): on the alloc_transport() failure path, decrement active_num_conn gated on server_conf.max_connections. Repro details: with the patch reverted, forced alloc_transport() NULL returns leaked counter slots and subsequent connection attempts -- including legitimate connects issued after the forced-fail window had closed -- were all rejected with "Limit the maximum number of connections". With this patch applied, the same connect sequence produces no rejections and the counter cycles cleanly between zero and one on every accept.

Weaknesses 1

Affected Products 10

References 7

• git.kernel.org https://git.kernel.org/stable/c/283027aa93380380a0994f35dde3ec95318f2654
  Patch
• git.kernel.org https://git.kernel.org/stable/c/295a9fc6789d1011c36ded9f0f2907bb34fa0de4
  Patch
• git.kernel.org https://git.kernel.org/stable/c/60734c8bc3b4aa0672e251f08dda81977e4b5387
• git.kernel.org https://git.kernel.org/stable/c/6551300dc452ac16a855a83dbd1e74899542d3b3
  Patch
• git.kernel.org https://git.kernel.org/stable/c/97f8d2648ef4871e4cd335e2d769cb40054a6772
  Patch
• git.kernel.org https://git.kernel.org/stable/c/dc2e7d595d68cf1be1ba64e3d30ebf3266bf7242
• git.kernel.org https://git.kernel.org/stable/c/fb48185bcd946d42de7017cf27f912f8ab26acf0
  Patch

Remediation

• git.kernel.org https://git.kernel.org/stable/c/283027aa93380380a0994f35dde3ec95318f2654
  Patch
• git.kernel.org https://git.kernel.org/stable/c/295a9fc6789d1011c36ded9f0f2907bb34fa0de4
  Patch
• git.kernel.org https://git.kernel.org/stable/c/6551300dc452ac16a855a83dbd1e74899542d3b3
  Patch
• git.kernel.org https://git.kernel.org/stable/c/97f8d2648ef4871e4cd335e2d769cb40054a6772
  Patch
• git.kernel.org https://git.kernel.org/stable/c/fb48185bcd946d42de7017cf27f912f8ab26acf0
  Patch