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author | Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp> | 2021-09-02 09:07:35 +0900 |
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committer | Jens Axboe <axboe@kernel.dk> | 2021-09-03 22:14:40 -0600 |
commit | 1c500ad706383f1a6609e63d0b5d1723fd84dab9 (patch) | |
tree | 7d357222d3bfee2fcaba6b013e025b62e42a4ff0 /drivers/block | |
parent | 0ef47db1cb64a9a226e8983e8b2691f8e1c02a37 (diff) | |
download | linux-1c500ad706383f1a6609e63d0b5d1723fd84dab9.tar.bz2 |
loop: reduce the loop_ctl_mutex scope
syzbot is reporting circular locking problem at __loop_clr_fd() [1], for
commit a160c6159d4a0cf8 ("block: add an optional probe callback to
major_names") is calling the module's probe function with major_names_lock
held.
Fortunately, since commit 990e78116d38059c ("block: loop: fix deadlock
between open and remove") stopped holding loop_ctl_mutex in lo_open(),
current role of loop_ctl_mutex is to serialize access to loop_index_idr
and loop_add()/loop_remove(); in other words, management of id for IDR.
To avoid holding loop_ctl_mutex during whole add/remove operation, use
a bool flag to indicate whether the loop device is ready for use.
loop_unregister_transfer() which is called from cleanup_cryptoloop()
currently has possibility of use-after-free problem due to lack of
serialization between kfree() from loop_remove() from loop_control_remove()
and mutex_lock() from unregister_transfer_cb(). But since lo->lo_encryption
should be already NULL when this function is called due to module unload,
and commit 222013f9ac30b9ce ("cryptoloop: add a deprecation warning")
indicates that we will remove this function shortly, this patch updates
this function to emit warning instead of checking lo->lo_encryption.
Holding loop_ctl_mutex in loop_exit() is pointless, for all users must
close /dev/loop-control and /dev/loop$num (in order to drop module's
refcount to 0) before loop_exit() starts, and nobody can open
/dev/loop-control or /dev/loop$num afterwards.
Link: https://syzkaller.appspot.com/bug?id=7bb10e8b62f83e4d445cdf4c13d69e407e629558 [1]
Reported-by: syzbot <syzbot+f61766d5763f9e7a118f@syzkaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/adb1e792-fc0e-ee81-7ea0-0906fc36419d@i-love.sakura.ne.jp
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'drivers/block')
-rw-r--r-- | drivers/block/loop.c | 75 | ||||
-rw-r--r-- | drivers/block/loop.h | 1 |
2 files changed, 50 insertions, 26 deletions
diff --git a/drivers/block/loop.c b/drivers/block/loop.c index fa1c298a8cfb..7bf4686af774 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -2111,18 +2111,6 @@ int loop_register_transfer(struct loop_func_table *funcs) return 0; } -static int unregister_transfer_cb(int id, void *ptr, void *data) -{ - struct loop_device *lo = ptr; - struct loop_func_table *xfer = data; - - mutex_lock(&lo->lo_mutex); - if (lo->lo_encryption == xfer) - loop_release_xfer(lo); - mutex_unlock(&lo->lo_mutex); - return 0; -} - int loop_unregister_transfer(int number) { unsigned int n = number; @@ -2130,9 +2118,20 @@ int loop_unregister_transfer(int number) if (n == 0 || n >= MAX_LO_CRYPT || (xfer = xfer_funcs[n]) == NULL) return -EINVAL; + /* + * This function is called from only cleanup_cryptoloop(). + * Given that each loop device that has a transfer enabled holds a + * reference to the module implementing it we should never get here + * with a transfer that is set (unless forced module unloading is + * requested). Thus, check module's refcount and warn if this is + * not a clean unloading. + */ +#ifdef CONFIG_MODULE_UNLOAD + if (xfer->owner && module_refcount(xfer->owner) != -1) + pr_err("Danger! Unregistering an in use transfer function.\n"); +#endif xfer_funcs[n] = NULL; - idr_for_each(&loop_index_idr, &unregister_transfer_cb, xfer); return 0; } @@ -2323,8 +2322,9 @@ static int loop_add(int i) } else { err = idr_alloc(&loop_index_idr, lo, 0, 0, GFP_KERNEL); } + mutex_unlock(&loop_ctl_mutex); if (err < 0) - goto out_unlock; + goto out_free_dev; i = err; err = -ENOMEM; @@ -2393,15 +2393,19 @@ static int loop_add(int i) disk->events = DISK_EVENT_MEDIA_CHANGE; disk->event_flags = DISK_EVENT_FLAG_UEVENT; sprintf(disk->disk_name, "loop%d", i); + /* Make this loop device reachable from pathname. */ add_disk(disk); + /* Show this loop device. */ + mutex_lock(&loop_ctl_mutex); + lo->idr_visible = true; mutex_unlock(&loop_ctl_mutex); return i; out_cleanup_tags: blk_mq_free_tag_set(&lo->tag_set); out_free_idr: + mutex_lock(&loop_ctl_mutex); idr_remove(&loop_index_idr, i); -out_unlock: mutex_unlock(&loop_ctl_mutex); out_free_dev: kfree(lo); @@ -2411,9 +2415,14 @@ out: static void loop_remove(struct loop_device *lo) { + /* Make this loop device unreachable from pathname. */ del_gendisk(lo->lo_disk); blk_cleanup_disk(lo->lo_disk); blk_mq_free_tag_set(&lo->tag_set); + mutex_lock(&loop_ctl_mutex); + idr_remove(&loop_index_idr, lo->lo_number); + mutex_unlock(&loop_ctl_mutex); + /* There is no route which can find this loop device. */ mutex_destroy(&lo->lo_mutex); kfree(lo); } @@ -2437,31 +2446,40 @@ static int loop_control_remove(int idx) return -EINVAL; } + /* Hide this loop device for serialization. */ ret = mutex_lock_killable(&loop_ctl_mutex); if (ret) return ret; - lo = idr_find(&loop_index_idr, idx); - if (!lo) { + if (!lo || !lo->idr_visible) ret = -ENODEV; - goto out_unlock_ctrl; - } + else + lo->idr_visible = false; + mutex_unlock(&loop_ctl_mutex); + if (ret) + return ret; + /* Check whether this loop device can be removed. */ ret = mutex_lock_killable(&lo->lo_mutex); if (ret) - goto out_unlock_ctrl; + goto mark_visible; if (lo->lo_state != Lo_unbound || atomic_read(&lo->lo_refcnt) > 0) { mutex_unlock(&lo->lo_mutex); ret = -EBUSY; - goto out_unlock_ctrl; + goto mark_visible; } + /* Mark this loop device no longer open()-able. */ lo->lo_state = Lo_deleting; mutex_unlock(&lo->lo_mutex); - idr_remove(&loop_index_idr, lo->lo_number); loop_remove(lo); -out_unlock_ctrl: + return 0; + +mark_visible: + /* Show this loop device again. */ + mutex_lock(&loop_ctl_mutex); + lo->idr_visible = true; mutex_unlock(&loop_ctl_mutex); return ret; } @@ -2475,7 +2493,8 @@ static int loop_control_get_free(int idx) if (ret) return ret; idr_for_each_entry(&loop_index_idr, lo, id) { - if (lo->lo_state == Lo_unbound) + /* Hitting a race results in creating a new loop device which is harmless. */ + if (lo->idr_visible && data_race(lo->lo_state) == Lo_unbound) goto found; } mutex_unlock(&loop_ctl_mutex); @@ -2591,10 +2610,14 @@ static void __exit loop_exit(void) unregister_blkdev(LOOP_MAJOR, "loop"); misc_deregister(&loop_misc); - mutex_lock(&loop_ctl_mutex); + /* + * There is no need to use loop_ctl_mutex here, for nobody else can + * access loop_index_idr when this module is unloading (unless forced + * module unloading is requested). If this is not a clean unloading, + * we have no means to avoid kernel crash. + */ idr_for_each_entry(&loop_index_idr, lo, id) loop_remove(lo); - mutex_unlock(&loop_ctl_mutex); idr_destroy(&loop_index_idr); } diff --git a/drivers/block/loop.h b/drivers/block/loop.h index 1988899db63a..04c88dd6eabd 100644 --- a/drivers/block/loop.h +++ b/drivers/block/loop.h @@ -68,6 +68,7 @@ struct loop_device { struct blk_mq_tag_set tag_set; struct gendisk *lo_disk; struct mutex lo_mutex; + bool idr_visible; }; struct loop_cmd { |