smb: prevent use-after-free due to open_cached_dir error paths

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>

diff --git a/fs/smb/client/cached_dir.c b/fs/smb/client/cached_dir.c
index bb9d4c284ce5771628f95b74148024e7281fc121..06eb19dabb0ecc12e6f254cbeb3830db1d255882 100644 (file)
--- a/fs/smb/client/cached_dir.c
+++ b/fs/smb/client/cached_dir.c
@@ -348,6 +348,7 @@ oshr_free:
        SMB2_query_info_free(&rqst[1]);
        free_rsp_buf(resp_buftype[0], rsp_iov[0].iov_base);
        free_rsp_buf(resp_buftype[1], rsp_iov[1].iov_base);
+out:
        if (rc) {
                spin_lock(&cfids->cfid_list_lock);
                if (cfid->on_list) {
@@ -359,23 +360,14 @@ oshr_free:
                        /*
                         * 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.
+                        * lease. Release one here, and the second below.
                         */
                        cfid->has_lease = false;
-                       spin_unlock(&cfids->cfid_list_lock);
                        kref_put(&cfid->refcount, smb2_close_cached_fid);
-                       goto out;
                }
                spin_unlock(&cfids->cfid_list_lock);
-       }
-out:
-       if (rc) {
-               if (cfid->is_open)
-                       SMB2_close(0, cfid->tcon, cfid->fid.persistent_fid,
-                                  cfid->fid.volatile_fid);
-               free_cached_dir(cfid);
+
+               kref_put(&cfid->refcount, smb2_close_cached_fid);
        } else {
                *ret_cfid = cfid;
                atomic_inc(&tcon->num_remote_opens);
@@ -513,25 +505,24 @@ 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);
        }
 }
@@ -542,9 +533,6 @@ 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);
 }
 
@@ -562,6 +550,7 @@ 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
@@ -639,8 +628,14 @@ static void cfids_laundromat_worker(struct work_struct *work)
                        cfid->on_list = false;
                        list_move(&cfid->entry, &entry);
                        cfids->num_entries--;
-                       /* To prevent race with smb2_cached_lease_break() */
-                       kref_get(&cfid->refcount);
+                       if (cfid->has_lease) {
+                               /*
+                                * Our lease has not yet been cancelled from the
+                                * server. Steal that reference.
+                                */
+                               cfid->has_lease = false;
+                       } else
+                               kref_get(&cfid->refcount);
                }
        }
        spin_unlock(&cfids->cfid_list_lock);
@@ -652,17 +647,10 @@ static void cfids_laundromat_worker(struct work_struct *work)
                 * with it.
                 */
                cancel_work_sync(&cfid->lease_break);
-               if (cfid->has_lease) {
-                       /*
-                        * Our lease has not yet been 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);
        }
        queue_delayed_work(cifsiod_wq, &cfids->laundromat_work,