]> git.baikalelectronics.ru Git - kernel.git/commit
ext4: fix superblock checksum calculation race
authorConstantine Sapuntzakis <costa@purestorage.com>
Mon, 14 Sep 2020 16:10:14 +0000 (10:10 -0600)
committerTheodore Ts'o <tytso@mit.edu>
Sun, 18 Oct 2020 14:36:23 +0000 (10:36 -0400)
commite6d806b6c379f9cc904a1bdf2cb43619e2767518
tree061d645d569d85d456654578813b933adaac8d51
parent58ba1ffb351abd4dc5a3a592f0d99bba3feb846f
ext4: fix superblock checksum calculation race

The race condition could cause the persisted superblock checksum
to not match the contents of the superblock, causing the
superblock to be considered corrupt.

An example of the race follows.  A first thread is interrupted in the
middle of a checksum calculation. Then, another thread changes the
superblock, calculates a new checksum, and sets it. Then, the first
thread resumes and sets the checksum based on the older superblock.

To fix, serialize the superblock checksum calculation using the buffer
header lock. While a spinlock is sufficient, the buffer header is
already there and there is precedent for locking it (e.g. in
ext4_commit_super).

Tested the patch by booting up a kernel with the patch, creating
a filesystem and some files (including some orphans), and then
unmounting and remounting the file system.

Cc: stable@kernel.org
Signed-off-by: Constantine Sapuntzakis <costa@purestorage.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Suggested-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20200914161014.22275-1-costa@purestorage.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
fs/ext4/super.c