6.6-stable review patch. If anyone has any objections, please let me know.
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From: Yu Kuai yukuai3@huawei.com
commit 8542870237c3a48ff049b6c5df5f50c8728284fa upstream.
While iterating all_mddevs list from md_notify_reboot() and md_exit(), list_for_each_entry_safe is used, and this can race with deletint the next mddev, causing UAF:
t1: spin_lock //list_for_each_entry_safe(mddev, n, ...) mddev_get(mddev1) // assume mddev2 is the next entry spin_unlock t2: //remove mddev2 ... mddev_free spin_lock list_del spin_unlock kfree(mddev2) mddev_put(mddev1) spin_lock //continue dereference mddev2->all_mddevs
The old helper for_each_mddev() actually grab the reference of mddev2 while holding the lock, to prevent from being freed. This problem can be fixed the same way, however, the code will be complex.
Hence switch to use list_for_each_entry, in this case mddev_put() can free the mddev1 and it's not safe as well. Refer to md_seq_show(), also factor out a helper mddev_put_locked() to fix this problem.
Cc: Christoph Hellwig hch@lst.de Link: https://lore.kernel.org/linux-raid/20250220124348.845222-1-yukuai1@huaweiclo... Fixes: f26514342255 ("md: stop using for_each_mddev in md_notify_reboot") Fixes: 16648bac862f ("md: stop using for_each_mddev in md_exit") Reported-and-tested-by: Guillaume Morin guillaume@morinfr.org Closes: https://lore.kernel.org/all/Z7Y0SURoA8xwg7vn@bender.morinfr.org/ Signed-off-by: Yu Kuai yukuai3@huawei.com Reviewed-by: Christoph Hellwig hch@lst.de Cc: Salvatore Bonaccorso carnil@debian.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/md/md.c | 22 +++++++++++++--------- 1 file changed, 13 insertions(+), 9 deletions(-)
--- a/drivers/md/md.c +++ b/drivers/md/md.c @@ -649,6 +649,12 @@ static void __mddev_put(struct mddev *md queue_work(md_misc_wq, &mddev->del_work); }
+static void mddev_put_locked(struct mddev *mddev) +{ + if (atomic_dec_and_test(&mddev->active)) + __mddev_put(mddev); +} + void mddev_put(struct mddev *mddev) { if (!atomic_dec_and_lock(&mddev->active, &all_mddevs_lock)) @@ -8417,9 +8423,7 @@ static int md_seq_show(struct seq_file * if (mddev == list_last_entry(&all_mddevs, struct mddev, all_mddevs)) status_unused(seq);
- if (atomic_dec_and_test(&mddev->active)) - __mddev_put(mddev); - + mddev_put_locked(mddev); return 0; }
@@ -9699,11 +9703,11 @@ EXPORT_SYMBOL_GPL(rdev_clear_badblocks); static int md_notify_reboot(struct notifier_block *this, unsigned long code, void *x) { - struct mddev *mddev, *n; + struct mddev *mddev; int need_delay = 0;
spin_lock(&all_mddevs_lock); - list_for_each_entry_safe(mddev, n, &all_mddevs, all_mddevs) { + list_for_each_entry(mddev, &all_mddevs, all_mddevs) { if (!mddev_get(mddev)) continue; spin_unlock(&all_mddevs_lock); @@ -9715,8 +9719,8 @@ static int md_notify_reboot(struct notif mddev_unlock(mddev); } need_delay = 1; - mddev_put(mddev); spin_lock(&all_mddevs_lock); + mddev_put_locked(mddev); } spin_unlock(&all_mddevs_lock);
@@ -10039,7 +10043,7 @@ void md_autostart_arrays(int part)
static __exit void md_exit(void) { - struct mddev *mddev, *n; + struct mddev *mddev; int delay = 1;
unregister_blkdev(MD_MAJOR,"md"); @@ -10060,7 +10064,7 @@ static __exit void md_exit(void) remove_proc_entry("mdstat", NULL);
spin_lock(&all_mddevs_lock); - list_for_each_entry_safe(mddev, n, &all_mddevs, all_mddevs) { + list_for_each_entry(mddev, &all_mddevs, all_mddevs) { if (!mddev_get(mddev)) continue; spin_unlock(&all_mddevs_lock); @@ -10072,8 +10076,8 @@ static __exit void md_exit(void) * the mddev for destruction by a workqueue, and the * destroy_workqueue() below will wait for that to complete. */ - mddev_put(mddev); spin_lock(&all_mddevs_lock); + mddev_put_locked(mddev); } spin_unlock(&all_mddevs_lock);