On 01/26/2018 09:20 PM, Nikolay Borisov wrote:
Commit 4fde46f0cc71 ("Btrfs: free the stale device") introduced btrfs_free_stale_device which iterates the device lists for all registered btrfs filesystems and deletes those devices which aren't mounted. In a btrfs_devices structure has only 1 device attached to it and it is unused then btrfs_free_stale_devices will proceed to also free the btrfs_fs_devices struct itself. Currently this leads to a UAF since list_for_each_entry will try to perform a check on the already- freed memory to see if it has to terminated the loop. The fix is to use 'break' when we know we are freeing the current fs_devs.
No break is needed as we need to iterate all stale devices and delete the found stale entry, so commit [1] used list_for_each_entry_safe() and removed the break, [1] commit 38cf665d338fca33af4b16f9ec7cad6637fc0fec Author: Anand Jain <anand.j...@oracle.com> btrfs: make btrfs_free_stale_device() to iterate all stales I am guessing UAF might be in[2], instead ? [2] free_fs_devices(fs_devs) :: while (!list_empty(&fs_devices->devices)) { device = list_entry(fs_devices->devices.next, struct btrfs_device, dev_list); Thanks, Anand
Fixes: 4fde46f0cc71 ("Btrfs: free the stale device") Signed-off-by: Nikolay Borisov <nbori...@suse.com>
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--- fs/btrfs/volumes.c | 1 + 1 file changed, 1 insertion(+) diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index f7147740b68e..c3ab55336ee0 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -645,6 +645,7 @@ static void btrfs_free_stale_devices(const char *path, btrfs_sysfs_remove_fsid(fs_devs); list_del(&fs_devs->list); free_fs_devices(fs_devs); + break; } else { fs_devs->num_devices--; list_del(&dev->dev_list);
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