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| author | Ryusuke Konishi <konishi.ryusuke@gmail.com> | 2022-11-04 23:29:59 +0900 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2022-11-16 09:58:26 +0100 |
| commit | afbd1188382a75f6cfe22c0b68533f7f9664f182 (patch) | |
| tree | 64778a0643b5c9155b36a9230a3b2e1de5a57411 | |
| parent | abc082aac0d9b6b926038fc3adb7008306581be2 (diff) | |
| download | linux-afbd1188382a75f6cfe22c0b68533f7f9664f182.tar.gz linux-afbd1188382a75f6cfe22c0b68533f7f9664f182.tar.bz2 linux-afbd1188382a75f6cfe22c0b68533f7f9664f182.zip | |
nilfs2: fix use-after-free bug of ns_writer on remount
commit 8cccf05fe857a18ee26e20d11a8455a73ffd4efd upstream.
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | fs/nilfs2/segment.c | 15 | ||||
| -rw-r--r-- | fs/nilfs2/super.c | 2 |
2 files changed, 8 insertions, 9 deletions
diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c index 96c5cab5c8ae..6d21f9bc6de1 100644 --- a/fs/nilfs2/segment.c +++ b/fs/nilfs2/segment.c @@ -317,7 +317,7 @@ void nilfs_relax_pressure_in_lock(struct super_block *sb) struct the_nilfs *nilfs = sb->s_fs_info; struct nilfs_sc_info *sci = nilfs->ns_writer; - if (!sci || !sci->sc_flush_request) + if (sb_rdonly(sb) || unlikely(!sci) || !sci->sc_flush_request) return; set_bit(NILFS_SC_PRIOR_FLUSH, &sci->sc_flags); @@ -2243,7 +2243,7 @@ int nilfs_construct_segment(struct super_block *sb) struct nilfs_transaction_info *ti; int err; - if (!sci) + if (sb_rdonly(sb) || unlikely(!sci)) return -EROFS; /* A call inside transactions causes a deadlock. */ @@ -2282,7 +2282,7 @@ int nilfs_construct_dsync_segment(struct super_block *sb, struct inode *inode, struct nilfs_transaction_info ti; int err = 0; - if (!sci) + if (sb_rdonly(sb) || unlikely(!sci)) return -EROFS; nilfs_transaction_lock(sb, &ti, 0); @@ -2778,11 +2778,12 @@ int nilfs_attach_log_writer(struct super_block *sb, struct nilfs_root *root) if (nilfs->ns_writer) { /* - * This happens if the filesystem was remounted - * read/write after nilfs_error degenerated it into a - * read-only mount. + * This happens if the filesystem is made read-only by + * __nilfs_error or nilfs_remount and then remounted + * read/write. In these cases, reuse the existing + * writer. */ - nilfs_detach_log_writer(sb); + return 0; } nilfs->ns_writer = nilfs_segctor_new(sb, root); diff --git a/fs/nilfs2/super.c b/fs/nilfs2/super.c index 2883ab625f61..663e68c22db8 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; /* |