Btrfs: fix use-after-free in the finishing procedure of the device replace

During device replace test, we hit a null pointer deference (It was very easy
to reproduce it by running xfstests' btrfs/011 on the devices with the virtio
scsi driver). There were two bugs that caused this problem:
- We might allocate new chunks on the replaced device after we updated
  the mapping tree. And we forgot to replace the source device in those
  mapping of the new chunks.
- We might get the mapping information which including the source device
  before the mapping information update. And then submit the bio which was
  based on that mapping information after we freed the source device.

For the first bug, we can fix it by doing mapping tree update and source
device remove in the same context of the chunk mutex. The chunk mutex is
used to protect the allocable device list, the above method can avoid
the new chunk allocation, and after we remove the source device, all
the new chunks will be allocated on the new device. So it can fix
the first bug.

For the second bug, we need make sure all flighting bios are finished and
no new bios are produced during we are removing the source device. To fix
this problem, we introduced a global @bio_counter, we not only inc/dec
@bio_counter outsize of map_blocks, but also inc it before submitting bio
and dec @bio_counter when ending bios.

Since Raid56 is a little different and device replace dosen't support raid56
yet, it is not addressed in the patch and I add comments to make sure we will
fix it in the future.

Reported-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: Wang Shilong <wangsl.fnst@cn.fujitsu.com>
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>

1 files changed, 23 insertions, 7 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index b68afe32419f..07629e99809a 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -5263,6 +5263,7 @@ int btrfs_rmap_block(struct btrfs_mapping_tree *map_tree,
 static void btrfs_end_bio(struct bio *bio, int err)
 {
 	struct btrfs_bio *bbio = bio->bi_private;
+	struct btrfs_device *dev = bbio->stripes[0].dev;
 	int is_orig_bio = 0;
 
 	if (err) {
@@ -5270,7 +5271,6 @@ static void btrfs_end_bio(struct bio *bio, int err)
 		if (err == -EIO || err == -EREMOTEIO) {
 			unsigned int stripe_index =
 				btrfs_io_bio(bio)->stripe_index;
-			struct btrfs_device *dev;
 
 			BUG_ON(stripe_index >= bbio->num_stripes);
 			dev = bbio->stripes[stripe_index].dev;
@@ -5292,6 +5292,8 @@ static void btrfs_end_bio(struct bio *bio, int err)
 	if (bio == bbio->orig_bio)
 		is_orig_bio = 1;
 
+	btrfs_bio_counter_dec(bbio->fs_info);
+
 	if (atomic_dec_and_test(&bbio->stripes_pending)) {
 		if (!is_orig_bio) {
 			bio_put(bio);
@@ -5440,6 +5442,9 @@ static void submit_stripe_bio(struct btrfs_root *root, struct btrfs_bio *bbio,
 	}
 #endif
 	bio->bi_bdev = dev->bdev;
+
+	btrfs_bio_counter_inc_noblocked(root->fs_info);
+
 	if (async)
 		btrfs_schedule_bio(root, dev, rw, bio);
 	else
@@ -5508,28 +5513,38 @@ int btrfs_map_bio(struct btrfs_root *root, int rw, struct bio *bio,
 	length = bio->bi_size;
 	map_length = length;
 
+	btrfs_bio_counter_inc_blocked(root->fs_info);
 	ret = __btrfs_map_block(root->fs_info, rw, logical, &map_length, &bbio,
 			      mirror_num, &raid_map);
-	if (ret) /* -ENOMEM */
+	if (ret) {
+		btrfs_bio_counter_dec(root->fs_info);
 		return ret;
+	}
 
 	total_devs = bbio->num_stripes;
 	bbio->orig_bio = first_bio;
 	bbio->private = first_bio->bi_private;
 	bbio->end_io = first_bio->bi_end_io;
+	bbio->fs_info = root->fs_info;
 	atomic_set(&bbio->stripes_pending, bbio->num_stripes);
 
 	if (raid_map) {
 		/* In this case, map_length has been set to the length of
 		   a single stripe; not the whole write */
 		if (rw & WRITE) {
-			return raid56_parity_write(root, bio, bbio,
-						   raid_map, map_length);
+			ret = raid56_parity_write(root, bio, bbio,
+						  raid_map, map_length);
 		} else {
-			return raid56_parity_recover(root, bio, bbio,
-						     raid_map, map_length,
-						     mirror_num);
+			ret = raid56_parity_recover(root, bio, bbio,
+						    raid_map, map_length,
+						    mirror_num);
 		}
+		/*
+		 * FIXME, replace dosen't support raid56 yet, please fix
+		 * it in the future.
+		 */
+		btrfs_bio_counter_dec(root->fs_info);
+		return ret;
 	}
 
 	if (map_length < length) {
@@ -5571,6 +5586,7 @@ int btrfs_map_bio(struct btrfs_root *root, int rw, struct bio *bio,
 				  async_submit);
 		dev_nr++;
 	}
+	btrfs_bio_counter_dec(root->fs_info);
 	return 0;
 }