[PATCH 5.4 023/348] btrfs: send: fix invalid path for unlink operations after parent orphanization

From: Greg Kroah-Hartman
Date: Mon Jul 12 2021 - 02:18:15 EST

From: Filipe Manana <fdmanana@xxxxxxxx>

commit d8ac76cdd1755b21e8c008c28d0b7251c0b14986 upstream.

During an incremental send operation, when processing the new references
for the current inode, we might send an unlink operation for another inode
that has a conflicting path and has more than one hard link. However this
path was computed and cached before we processed previous new references
for the current inode. We may have orphanized a directory of that path
while processing a previous new reference, in which case the path will
be invalid and cause the receiver process to fail.

The following reproducer triggers the problem and explains how/why it
happens in its comments:

$ cat test-send-unlink.sh


mkfs.btrfs -f $DEV >/dev/null
mount $DEV $MNT

# Create our test files and directory. Inode 259 (file3) has two hard
# links.
touch $MNT/file1
touch $MNT/file2
touch $MNT/file3

mkdir $MNT/A
ln $MNT/file3 $MNT/A/hard_link

# Filesystem looks like:
# . (ino 256)
# |----- file1 (ino 257)
# |----- file2 (ino 258)
# |----- file3 (ino 259)
# |----- A/ (ino 260)
# |---- hard_link (ino 259)

# Now create the base snapshot, which is going to be the parent snapshot
# for a later incremental send.
btrfs subvolume snapshot -r $MNT $MNT/snap1
btrfs send -f /tmp/snap1.send $MNT/snap1

# Move inode 257 into directory inode 260. This results in computing the
# path for inode 260 as "/A" and caching it.
mv $MNT/file1 $MNT/A/file1

# Move inode 258 (file2) into directory inode 260, with a name of
# "hard_link", moving first inode 259 away since it currently has that
# location and name.
mv $MNT/A/hard_link $MNT/tmp
mv $MNT/file2 $MNT/A/hard_link

# Now rename inode 260 to something else (B for example) and then create
# a hard link for inode 258 that has the old name and location of inode
# 260 ("/A").
mv $MNT/A $MNT/B
ln $MNT/B/hard_link $MNT/A

# Filesystem now looks like:
# . (ino 256)
# |----- tmp (ino 259)
# |----- file3 (ino 259)
# |----- B/ (ino 260)
# | |---- file1 (ino 257)
# | |---- hard_link (ino 258)
# |
# |----- A (ino 258)

# Create another snapshot of our subvolume and use it for an incremental
# send.
btrfs subvolume snapshot -r $MNT $MNT/snap2
btrfs send -f /tmp/snap2.send -p $MNT/snap1 $MNT/snap2

# Now unmount the filesystem, create a new one, mount it and try to
# apply both send streams to recreate both snapshots.
umount $DEV

mkfs.btrfs -f $DEV >/dev/null

mount $DEV $MNT

# First add the first snapshot to the new filesystem by applying the
# first send stream.
btrfs receive -f /tmp/snap1.send $MNT

# The incremental receive operation below used to fail with the
# following error:
# ERROR: unlink A/hard_link failed: No such file or directory
# This is because when send is processing inode 257, it generates the
# path for inode 260 as "/A", since that inode is its parent in the send
# snapshot, and caches that path.
# Later when processing inode 258, it first processes its new reference
# that has the path of "/A", which results in orphanizing inode 260
# because there is a a path collision. This results in issuing a rename
# operation from "/A" to "/o260-6-0".
# Finally when processing the new reference "B/hard_link" for inode 258,
# it notices that it collides with inode 259 (not yet processed, because
# it has a higher inode number), since that inode has the name
# "hard_link" under the directory inode 260. It also checks that inode
# 259 has two hardlinks, so it decides to issue a unlink operation for
# the name "hard_link" for inode 259. However the path passed to the
# unlink operation is "/A/hard_link", which is incorrect since currently
# "/A" does not exists, due to the orphanization of inode 260 mentioned
# before. The path is incorrect because it was computed and cached
# before the orphanization. This results in the receiver to fail with
# the above error.
btrfs receive -f /tmp/snap2.send $MNT

umount $MNT

When running the test, it fails like this:

$ ./test-send-unlink.sh
Create a readonly snapshot of '/mnt/sdi' in '/mnt/sdi/snap1'
At subvol /mnt/sdi/snap1
Create a readonly snapshot of '/mnt/sdi' in '/mnt/sdi/snap2'
At subvol /mnt/sdi/snap2
At subvol snap1
At snapshot snap2
ERROR: unlink A/hard_link failed: No such file or directory

Fix this by recomputing a path before issuing an unlink operation when
processing the new references for the current inode if we previously
have orphanized a directory.

A test case for fstests will follow soon.

CC: stable@xxxxxxxxxxxxxxx # 4.4+
Signed-off-by: Filipe Manana <fdmanana@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

fs/btrfs/send.c | 11 +++++++++++
1 file changed, 11 insertions(+)

--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -4087,6 +4087,17 @@ static int process_recorded_refs(struct
if (ret < 0)
goto out;
} else {
+ /*
+ * If we previously orphanized a directory that
+ * collided with a new reference that we already
+ * processed, recompute the current path because
+ * that directory may be part of the path.
+ */
+ if (orphanized_dir) {
+ ret = refresh_ref_path(sctx, cur);
+ if (ret < 0)
+ goto out;
+ }
ret = send_unlink(sctx, cur->full_path);
if (ret < 0)
goto out;