[PATCH v6.1] smb: prevent use-after-free due to open_cached_dir error paths

[PATCH v6.1] smb: prevent use-after-free due to open_cached_dir error paths

[Shivani Agarwal]

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;
+		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

Re: [PATCH v6.1] smb: prevent use-after-free due to open_cached_dir error paths

[Paul Aurich]

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

Re: [PATCH v6.1] smb: prevent use-after-free due to open_cached_dir error paths

[Greg KH]

On Thu, Oct 09, 2025 at 08:00:33PM -0700, Paul Aurich wrote:
> 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.

Now dropped from the queue, thanks for the review.

greg k-h