Thanks for proposing this! I think this backport has the problem I was concerned with when Cliff Liu proposed a backport in March [1].

The handling of the 'has_lease' field in this patch depends on work done by two other patches, and those should be backported before this one:

- 5c86919455c1 ("smb: client: fix use-after-free in smb2_query_info_compound()") - 7afb86733685 ("smb: Don't leak cfid when reconnect races with open_cached_dir")

I have (somewhere...) a backport of all three of these patches three patches to linux-6.1.y, but it was a while ago and I never found the time to _test_ the backports.

[1] https://lore.kernel.org/linux-cifs/Z9uGCaxYJgs1gvwM@vaarsuvius.home.arpa/

On 2025-10-08 23:08:46 -0700, Shivani Agarwal wrote:

From: Paul Aurich paul@darkrain42.org

commit a9685b409a03b73d2980bbfa53eb47555802d0a9 upstream.

If open_cached_dir() encounters an error parsing the lease from the server, the error handling may race with receiving a lease break, resulting in open_cached_dir() freeing the cfid while the queued work is pending.

Update open_cached_dir() to drop refs rather than directly freeing the cfid.

Have cached_dir_lease_break(), cfids_laundromat_worker(), and invalidate_all_cached_dirs() clear has_lease immediately while still holding cfids->cfid_list_lock, and then use this to also simplify the reference counting in cfids_laundromat_worker() and invalidate_all_cached_dirs().

Fixes this KASAN splat (which manually injects an error and lease break in open_cached_dir()):

================================================================== BUG: KASAN: slab-use-after-free in smb2_cached_lease_break+0x27/0xb0 Read of size 8 at addr ffff88811cc24c10 by task kworker/3:1/65

CPU: 3 UID: 0 PID: 65 Comm: kworker/3:1 Not tainted 6.12.0-rc6-g255cf264e6e5-dirty #87 Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 11/12/2020 Workqueue: cifsiod smb2_cached_lease_break Call Trace:

<TASK> dump_stack_lvl+0x77/0xb0 print_report+0xce/0x660 kasan_report+0xd3/0x110 smb2_cached_lease_break+0x27/0xb0 process_one_work+0x50a/0xc50 worker_thread+0x2ba/0x530 kthread+0x17c/0x1c0 ret_from_fork+0x34/0x60 ret_from_fork_asm+0x1a/0x30 </TASK>

Allocated by task 2464: kasan_save_stack+0x33/0x60 kasan_save_track+0x14/0x30 __kasan_kmalloc+0xaa/0xb0 open_cached_dir+0xa7d/0x1fb0 smb2_query_path_info+0x43c/0x6e0 cifs_get_fattr+0x346/0xf10 cifs_get_inode_info+0x157/0x210 cifs_revalidate_dentry_attr+0x2d1/0x460 cifs_getattr+0x173/0x470 vfs_statx_path+0x10f/0x160 vfs_statx+0xe9/0x150 vfs_fstatat+0x5e/0xc0 __do_sys_newfstatat+0x91/0xf0 do_syscall_64+0x95/0x1a0 entry_SYSCALL_64_after_hwframe+0x76/0x7e

Freed by task 2464: kasan_save_stack+0x33/0x60 kasan_save_track+0x14/0x30 kasan_save_free_info+0x3b/0x60 __kasan_slab_free+0x51/0x70 kfree+0x174/0x520 open_cached_dir+0x97f/0x1fb0 smb2_query_path_info+0x43c/0x6e0 cifs_get_fattr+0x346/0xf10 cifs_get_inode_info+0x157/0x210 cifs_revalidate_dentry_attr+0x2d1/0x460 cifs_getattr+0x173/0x470 vfs_statx_path+0x10f/0x160 vfs_statx+0xe9/0x150 vfs_fstatat+0x5e/0xc0 __do_sys_newfstatat+0x91/0xf0 do_syscall_64+0x95/0x1a0 entry_SYSCALL_64_after_hwframe+0x76/0x7e

Last potentially related work creation: kasan_save_stack+0x33/0x60 __kasan_record_aux_stack+0xad/0xc0 insert_work+0x32/0x100 __queue_work+0x5c9/0x870 queue_work_on+0x82/0x90 open_cached_dir+0x1369/0x1fb0 smb2_query_path_info+0x43c/0x6e0 cifs_get_fattr+0x346/0xf10 cifs_get_inode_info+0x157/0x210 cifs_revalidate_dentry_attr+0x2d1/0x460 cifs_getattr+0x173/0x470 vfs_statx_path+0x10f/0x160 vfs_statx+0xe9/0x150 vfs_fstatat+0x5e/0xc0 __do_sys_newfstatat+0x91/0xf0 do_syscall_64+0x95/0x1a0 entry_SYSCALL_64_after_hwframe+0x76/0x7e

The buggy address belongs to the object at ffff88811cc24c00 which belongs to the cache kmalloc-1k of size 1024 The buggy address is located 16 bytes inside of freed 1024-byte region [ffff88811cc24c00, ffff88811cc25000)

Cc: stable@vger.kernel.org Signed-off-by: Paul Aurich paul@darkrain42.org Signed-off-by: Steve French stfrench@microsoft.com [ Do not apply the change for cfids_laundromat_worker() since there is no this function and related feature on 6.1.y. Update open_cached_dir() according to method of upstream patch. ] Signed-off-by: Cliff Liu donghua.liu@windriver.com Signed-off-by: He Zhe Zhe.He@windriver.com [Shivani: Modified to apply on 6.1.y] Signed-off-by: Shivani Agarwal shivani.agarwal@broadcom.com

---

fs/smb/client/cached_dir.c | 39 ++++++++++++++++---------------------- 1 file changed, 16 insertions(+), 23 deletions(-)

diff --git a/fs/smb/client/cached_dir.c b/fs/smb/client/cached_dir.c index 3d028b6a2..23a57a0c8 100644 --- a/fs/smb/client/cached_dir.c +++ b/fs/smb/client/cached_dir.c @@ -320,17 +320,13 @@ int open_cached_dir(unsigned int xid, struct cifs_tcon *tcon, /* * We are guaranteed to have two references at this point. * One for the caller and one for a potential lease.

•  * Release the Lease-ref so that the directory will be closed
  

•  * when the caller closes the cached handle.
  

•  * Release one here, and the second below.
  

  */ kref_put(&cfid->refcount, smb2_close_cached_fid); } if (rc) {

• if (cfid->is_open)
  

• 	SMB2_close(0, cfid->tcon, cfid->fid.persistent_fid,
  

• 		   cfid->fid.volatile_fid);
  

• free_cached_dir(cfid);
  

• cfid = NULL;
  

• cfid->has_lease = false;
  

cfid->has_lease needs to be cleared while holding cfids->cfid_list_lock. (See my feedback to the stable backport in March)

• kref_put(&cfid->refcount, smb2_close_cached_fid);
  

  }

  if (rc == 0) {

@@ -462,25 +458,24 @@ void invalidate_all_cached_dirs(struct cifs_tcon *tcon) cfids->num_entries--; cfid->is_open = false; cfid->on_list = false;

• /* To prevent race with smb2_cached_lease_break() */
  

• kref_get(&cfid->refcount);
  

• if (cfid->has_lease) {
  

• 	/*
  

• 	 * The lease was never cancelled from the server,
  

• 	 * so steal that reference.
  

• 	 */
  

• 	cfid->has_lease = false;
  

• } else
  

• 	kref_get(&cfid->refcount);
  

  } spin_unlock(&cfids->cfid_list_lock);

  list_for_each_entry_safe(cfid, q, &entry, entry) { list_del(&cfid->entry); cancel_work_sync(&cfid->lease_break);

• if (cfid->has_lease) {
  

• 	/*
  

• 	 * We lease was never cancelled from the server so we
  

• 	 * need to drop the reference.
  

• 	 */
  

• 	spin_lock(&cfids->cfid_list_lock);
  

• 	cfid->has_lease = false;
  

• 	spin_unlock(&cfids->cfid_list_lock);
  

• 	kref_put(&cfid->refcount, smb2_close_cached_fid);
  

• }
  

• /* Drop the extra reference opened above*/
  

• /*
  

•  * Drop the ref-count from above, either the lease-ref (if there
  

•  * was one) or the extra one acquired.
  

•  */
  

  kref_put(&cfid->refcount, smb2_close_cached_fid); }

} @@ -491,9 +486,6 @@ smb2_cached_lease_break(struct work_struct *work) struct cached_fid *cfid = container_of(work, struct cached_fid, lease_break);

• spin_lock(&cfid->cfids->cfid_list_lock);
• cfid->has_lease = false;
• spin_unlock(&cfid->cfids->cfid_list_lock); kref_put(&cfid->refcount, smb2_close_cached_fid);

}

@@ -511,6 +503,7 @@ int cached_dir_lease_break(struct cifs_tcon *tcon, __u8 lease_key[16]) !memcmp(lease_key, cfid->fid.lease_key, SMB2_LEASE_KEY_SIZE)) {

• 	cfid->has_lease = false;
  cfid->time = 0;
  /*
   * We found a lease remove it from the list
  

-- 2.40.4

~Paul