[PATCH 5.15 103/230] btrfs: dont access possibly stale fs_info data in device_list_add

Greg Kroah-Hartman
2022-07-11T09:49:59Z

From: Dongliang Mu <mudongliangabcd@gmail.com>

[ Upstream commit 79c9234ba596e903907de20573fd4bcc85315b06 ]

Syzbot reported a possible use-after-free in printing information
in device_list_add.

Very similar with the bug fixed by commit 0697d9a61099 ("btrfs: don't
access possibly stale fs_info data for printing duplicate device"),
but this time the use occurs in btrfs_info_in_rcu.

Call Trace:
kasan_report.cold+0x83/0xdf mm/kasan/report.c:459
btrfs_printk+0x395/0x425 fs/btrfs/super.c:244
device_list_add.cold+0xd7/0x2ed fs/btrfs/volumes.c:957
btrfs_scan_one_device+0x4c7/0x5c0 fs/btrfs/volumes.c:1387
btrfs_control_ioctl+0x12a/0x2d0 fs/btrfs/super.c:2409
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]
__se_sys_ioctl fs/ioctl.c:860 [inline]
__x64_sys_ioctl+0x193/0x200 fs/ioctl.c:860
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae

Fix this by modifying device->fs_info to NULL too.

Reported-and-tested-by: syzbot+82650a4e0ed38f218363@syzkaller.appspotmail.com
CC: stable@vger.kernel.org # 4.19+
Signed-off-by: Dongliang Mu <mudongliangabcd@gmail.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/btrfs/volumes.c | 13 ++++++-------
1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index cec54c6e1cdd..89ce0b449c22 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -955,6 +955,11 @@ static noinline struct btrfs_device *device_list_add(const char *path,
/*
* We are going to replace the device path for a given devid,
* make sure it's the same device if the device is mounted
+ *
+ * NOTE: the device->fs_info may not be reliable here so pass
+ * in a NULL to message helpers instead. This avoids a possible
+ * use-after-free when the fs_info and fs_info->sb are already
+ * torn down.
*/
if (device->bdev) {
int error;
@@ -968,12 +973,6 @@ static noinline struct btrfs_device *device_list_add(const char *path,

if (device->bdev->bd_dev != path_dev) {
mutex_unlock(&fs_devices->device_list_mutex);
- /*
- * device->fs_info may not be reliable here, so
- * pass in a NULL instead. This avoids a
- * possible use-after-free when the fs_info and
- * fs_info->sb are already torn down.
- */
btrfs_warn_in_rcu(NULL,
"duplicate device %s devid %llu generation %llu scanned by %s (%d)",
path, devid, found_transid,
@@ -981,7 +980,7 @@ static noinline struct btrfs_device *device_list_add(const char *path,
task_pid_nr(current));
return ERR_PTR(-EEXIST);
}
- btrfs_info_in_rcu(device->fs_info,
+ btrfs_info_in_rcu(NULL,
"devid %llu device path %s changed to %s scanned by %s (%d)",
devid, rcu_str_deref(device->name),
path, current->comm,
--
2.35.1