Also would be good to see if we can isolate the umount race with
freeing cached dentries which I can occasionally reproduce to Windows
part way through a large XFS test (but never fails if directory leases
disabled)
On Wed, Mar 19, 2025 at 10:16 PM Paul Aurich <paul@xxxxxxxxxxxxxx> wrote:
>
> Thanks for backporting this! I think you should pick up these patches as
> pre-requisites for the one here:
>
> - 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")
>
> All three of these patches touch on how the cached directory handling of the
> 'has_lease' field works, and my work was built on top of those.
>
> On 2025-03-19 17:08:39 +0800, Cliff Liu wrote:
> >From: Paul Aurich <paul@xxxxxxxxxxxxxx>
> >
> >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@xxxxxxxxxxxxxxx
> >Signed-off-by: Paul Aurich <paul@xxxxxxxxxxxxxx>
> >Signed-off-by: Steve French <stfrench@xxxxxxxxxxxxx>
> >[ 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@xxxxxxxxxxxxx>
> >Signed-off-by: He Zhe <Zhe.He@xxxxxxxxxxxxx>
> >---
> >Verified the build test.
> >---
> > 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 d09226c1ac90..d65d5fe5b8fe 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;
>
> This should be cleared while holding cfids->cfid_list_lock, which is what the
> upstream version of this backport (a9685b409a0) does, because of how this
> error handling was adjusted in 5c86919455c1 ("smb: client: fix use-after-free
> in smb2_query_info_compound()")
>
> >+ 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
> >--
> >2.43.0
> >
>
> ~Paul
>
>
--
Thanks,
Steve
