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darkrain42smfrench
darkrain42
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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>
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‎fs/smb/client/cached_dir.c‎

Lines changed: 29 additions & 41 deletions
Original file line numberDiff line numberDiff line change
@@ -348,6 +348,7 @@ int open_cached_dir(unsigned int xid, struct cifs_tcon *tcon,
348348
SMB2_query_info_free(&rqst[1]);
349349
free_rsp_buf(resp_buftype[0], rsp_iov[0].iov_base);
350350
free_rsp_buf(resp_buftype[1], rsp_iov[1].iov_base);
351+
out:
351352
if (rc) {
352353
spin_lock(&cfids->cfid_list_lock);
353354
if (cfid->on_list) {
@@ -359,23 +360,14 @@ int open_cached_dir(unsigned int xid, struct cifs_tcon *tcon,
359360
/*
360361
* We are guaranteed to have two references at this
361362
* point. One for the caller and one for a potential
362-
* lease. Release the Lease-ref so that the directory
363-
* will be closed when the caller closes the cached
364-
* handle.
363+
* lease. Release one here, and the second below.
365364
*/
366365
cfid->has_lease = false;
367-
spin_unlock(&cfids->cfid_list_lock);
368366
kref_put(&cfid->refcount, smb2_close_cached_fid);
369-
goto out;
370367
}
371368
spin_unlock(&cfids->cfid_list_lock);
372-
}
373-
out:
374-
if (rc) {
375-
if (cfid->is_open)
376-
SMB2_close(0, cfid->tcon, cfid->fid.persistent_fid,
377-
cfid->fid.volatile_fid);
378-
free_cached_dir(cfid);
369+
370+
kref_put(&cfid->refcount, smb2_close_cached_fid);
379371
} else {
380372
*ret_cfid = cfid;
381373
atomic_inc(&tcon->num_remote_opens);
@@ -513,25 +505,24 @@ void invalidate_all_cached_dirs(struct cifs_tcon *tcon)
513505
cfids->num_entries--;
514506
cfid->is_open = false;
515507
cfid->on_list = false;
516-
/* To prevent race with smb2_cached_lease_break() */
517-
kref_get(&cfid->refcount);
508+
if (cfid->has_lease) {
509+
/*
510+
* The lease was never cancelled from the server,
511+
* so steal that reference.
512+
*/
513+
cfid->has_lease = false;
514+
} else
515+
kref_get(&cfid->refcount);
518516
}
519517
spin_unlock(&cfids->cfid_list_lock);
520518

521519
list_for_each_entry_safe(cfid, q, &entry, entry) {
522520
list_del(&cfid->entry);
523521
cancel_work_sync(&cfid->lease_break);
524-
if (cfid->has_lease) {
525-
/*
526-
* We lease was never cancelled from the server so we
527-
* need to drop the reference.
528-
*/
529-
spin_lock(&cfids->cfid_list_lock);
530-
cfid->has_lease = false;
531-
spin_unlock(&cfids->cfid_list_lock);
532-
kref_put(&cfid->refcount, smb2_close_cached_fid);
533-
}
534-
/* Drop the extra reference opened above*/
522+
/*
523+
* Drop the ref-count from above, either the lease-ref (if there
524+
* was one) or the extra one acquired.
525+
*/
535526
kref_put(&cfid->refcount, smb2_close_cached_fid);
536527
}
537528
}
@@ -542,9 +533,6 @@ smb2_cached_lease_break(struct work_struct *work)
542533
struct cached_fid *cfid = container_of(work,
543534
struct cached_fid, lease_break);
544535

545-
spin_lock(&cfid->cfids->cfid_list_lock);
546-
cfid->has_lease = false;
547-
spin_unlock(&cfid->cfids->cfid_list_lock);
548536
kref_put(&cfid->refcount, smb2_close_cached_fid);
549537
}
550538

@@ -562,6 +550,7 @@ int cached_dir_lease_break(struct cifs_tcon *tcon, __u8 lease_key[16])
562550
!memcmp(lease_key,
563551
cfid->fid.lease_key,
564552
SMB2_LEASE_KEY_SIZE)) {
553+
cfid->has_lease = false;
565554
cfid->time = 0;
566555
/*
567556
* We found a lease remove it from the list
@@ -639,8 +628,14 @@ static void cfids_laundromat_worker(struct work_struct *work)
639628
cfid->on_list = false;
640629
list_move(&cfid->entry, &entry);
641630
cfids->num_entries--;
642-
/* To prevent race with smb2_cached_lease_break() */
643-
kref_get(&cfid->refcount);
631+
if (cfid->has_lease) {
632+
/*
633+
* Our lease has not yet been cancelled from the
634+
* server. Steal that reference.
635+
*/
636+
cfid->has_lease = false;
637+
} else
638+
kref_get(&cfid->refcount);
644639
}
645640
}
646641
spin_unlock(&cfids->cfid_list_lock);
@@ -652,17 +647,10 @@ static void cfids_laundromat_worker(struct work_struct *work)
652647
* with it.
653648
*/
654649
cancel_work_sync(&cfid->lease_break);
655-
if (cfid->has_lease) {
656-
/*
657-
* Our lease has not yet been cancelled from the server
658-
* so we need to drop the reference.
659-
*/
660-
spin_lock(&cfids->cfid_list_lock);
661-
cfid->has_lease = false;
662-
spin_unlock(&cfids->cfid_list_lock);
663-
kref_put(&cfid->refcount, smb2_close_cached_fid);
664-
}
665-
/* Drop the extra reference opened above */
650+
/*
651+
* Drop the ref-count from above, either the lease-ref (if there
652+
* was one) or the extra one acquired.
653+
*/
666654
kref_put(&cfid->refcount, smb2_close_cached_fid);
667655
}
668656
queue_delayed_work(cifsiod_wq, &cfids->laundromat_work,

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