* [PATCH v6.1] smb: prevent use-after-free due to open_cached_dir error paths
@ 2025-10-09 6:08 Shivani Agarwal
2025-10-10 3:00 ` Paul Aurich
0 siblings, 1 reply; 3+ messages in thread
From: Shivani Agarwal @ 2025-10-09 6:08 UTC (permalink / raw)
To: stable, gregkh
Cc: bcm-kernel-feedback-list, linux-kernel, ajay.kaher,
alexey.makhalov, tapas.kundu, sfrench, pc, ronniesahlberg,
sprasad, tom, bharathsm, linux-cifs, samba-technical, Paul Aurich,
Steve French, Cliff Liu, He Zhe, 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
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH v6.1] smb: prevent use-after-free due to open_cached_dir error paths
2025-10-09 6:08 [PATCH v6.1] smb: prevent use-after-free due to open_cached_dir error paths Shivani Agarwal
@ 2025-10-10 3:00 ` Paul Aurich
2025-10-10 10:52 ` Greg KH
0 siblings, 1 reply; 3+ messages in thread
From: Paul Aurich @ 2025-10-10 3:00 UTC (permalink / raw)
To: Shivani Agarwal
Cc: stable, gregkh, bcm-kernel-feedback-list, linux-kernel,
ajay.kaher, alexey.makhalov, tapas.kundu, sfrench, pc,
ronniesahlberg, sprasad, tom, bharathsm, linux-cifs,
samba-technical, Steve French, Cliff Liu, He Zhe
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
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v6.1] smb: prevent use-after-free due to open_cached_dir error paths
2025-10-10 3:00 ` Paul Aurich
@ 2025-10-10 10:52 ` Greg KH
0 siblings, 0 replies; 3+ messages in thread
From: Greg KH @ 2025-10-10 10:52 UTC (permalink / raw)
To: Shivani Agarwal, stable, bcm-kernel-feedback-list, linux-kernel,
ajay.kaher, alexey.makhalov, tapas.kundu, sfrench, pc,
ronniesahlberg, sprasad, tom, bharathsm, linux-cifs,
samba-technical, Steve French, Cliff Liu, He Zhe
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
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2025-10-10 10:53 UTC | newest]
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2025-10-09 6:08 [PATCH v6.1] smb: prevent use-after-free due to open_cached_dir error paths Shivani Agarwal
2025-10-10 3:00 ` Paul Aurich
2025-10-10 10:52 ` Greg KH
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