diff options
| author |   Ryusuke Konishi <konishi.ryusuke@gmail.com> | 2022-11-04 23:29:59 +0900 |
|---|---|---|
| committer |   Andrew Morton <akpm@linux-foundation.org> | 2022-11-08 15:57:24 -0800 |
| commit | 8cccf05fe857a18ee26e20d11a8455a73ffd4efd (patch) | |
| tree | 220d5328e227275b24cf028eb00a4e852e028335 /fs/nilfs2/super.c | |
| parent | x86/traps: avoid KMSAN bugs originating from handle_bug() (diff) | |
| download | linux-dev-8cccf05fe857a18ee26e20d11a8455a73ffd4efd.tar.xz linux-dev-8cccf05fe857a18ee26e20d11a8455a73ffd4efd.zip | |
nilfs2: fix use-after-free bug of ns_writer on remount
If a nilfs2 filesystem is downgraded to read-only due to metadata
corruption on disk and is remounted read/write, or if emergency read-only
remount is performed, detaching a log writer and synchronizing the
filesystem can be done at the same time.
In these cases, use-after-free of the log writer (hereinafter
nilfs->ns_writer) can happen as shown in the scenario below:
Task1 Task2
-------------------------------- ------------------------------
nilfs_construct_segment
nilfs_segctor_sync
init_wait
init_waitqueue_entry
add_wait_queue
schedule
nilfs_remount (R/W remount case)
nilfs_attach_log_writer
nilfs_detach_log_writer
nilfs_segctor_destroy
kfree
finish_wait
_raw_spin_lock_irqsave
__raw_spin_lock_irqsave
do_raw_spin_lock
debug_spin_lock_before <-- use-after-free
While Task1 is sleeping, nilfs->ns_writer is freed by Task2. After Task1
waked up, Task1 accesses nilfs->ns_writer which is already freed. This
scenario diagram is based on the Shigeru Yoshida's post [1].
This patch fixes the issue by not detaching nilfs->ns_writer on remount so
that this UAF race doesn't happen. Along with this change, this patch
also inserts a few necessary read-only checks with superblock instance
where only the ns_writer pointer was used to check if the filesystem is
read-only.
Link: https://syzkaller.appspot.com/bug?id=79a4c002e960419ca173d55e863bd09e8112df8b
Link: https://lkml.kernel.org/r/20221103141759.1836312-1-syoshida@redhat.com [1]
Link: https://lkml.kernel.org/r/20221104142959.28296-1-konishi.ryusuke@gmail.com
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Reported-by: syzbot+f816fa82f8783f7a02bb@syzkaller.appspotmail.com
Reported-by: Shigeru Yoshida <syoshida@redhat.com>
Tested-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to '')
| -rw-r--r-- | fs/nilfs2/super.c | 2 |
1 files changed, 0 insertions, 2 deletions
diff --git a/fs/nilfs2/super.c b/fs/nilfs2/super.c index ba108f915391..6edb6e0dd61f 100644 --- a/fs/nilfs2/super.c +++ b/fs/nilfs2/super.c @@ -1133,8 +1133,6 @@ static int nilfs_remount(struct super_block *sb, int *flags, char *data) if ((bool)(*flags & SB_RDONLY) == sb_rdonly(sb)) goto out; if (*flags & SB_RDONLY) { - /* Shutting down log writer */ - nilfs_detach_log_writer(sb); sb->s_flags |= SB_RDONLY; /* |