[PATCH v2 2/3] blktrace: fix possible memleak in '__blk_trace_remove'

Ye Bin
2022-10-18T14:29:51Z

When test as follows:
step1: ioctl(sda, BLKTRACESETUP, &arg)
step2: ioctl(sda, BLKTRACESTART, NULL)
step3: ioctl(sda, BLKTRACETEARDOWN, NULL)
step4: ioctl(sda, BLKTRACESETUP, &arg)
Got issue as follows:
debugfs: File 'dropped' in directory 'sda' already present!
debugfs: File 'msg' in directory 'sda' already present!
debugfs: File 'trace0' in directory 'sda' already present!

And also find syzkaller report issue like "KASAN: use-after-free Read in relay_switch_subbuf"
"https://syzkaller.appspot.com/bug?id=13849f0d9b1b818b087341691be6cc3ac6a6bfb7"

If remove block trace without stop(BLKTRACESTOP) block trace, '__blk_trace_remove'
will just set 'q->blk_trace' with NULL. However, debugfs file isn't removed, so
will report file already present when call BLKTRACESETUP.
static int __blk_trace_remove(struct request_queue *q)
{
struct blk_trace *bt;

bt = rcu_replace_pointer(q->blk_trace, NULL,
lockdep_is_held(&q->debugfs_mutex));
if (!bt)
return -EINVAL;

if (bt->trace_state != Blktrace_running)
blk_trace_cleanup(q, bt);

return 0;
}

If do test as follows:
step1: ioctl(sda, BLKTRACESETUP, &arg)
step2: ioctl(sda, BLKTRACESTART, NULL)
step3: ioctl(sda, BLKTRACETEARDOWN, NULL)
step4: remove sda

There will remove debugfs directory which will remove recursively all file
under directory.
>> blk_release_queue
>> debugfs_remove_recursive(q->debugfs_dir)
So all files which created in 'do_blk_trace_setup' are removed, and
'dentry->d_inode' is NULL. But 'q->blk_trace' is still in 'running_trace_lock',
'trace_note_tsk' will traverse 'running_trace_lock' all nodes.
>>trace_note_tsk
>> trace_note
>> relay_reserve
>> relay_switch_subbuf
>> d_inode(buf->dentry)->i_size

To solve above issues, reference commit '5afedf670caf', call 'blk_trace_cleanup'
unconditionally in '__blk_trace_remove' and first stop block trace in
'blk_trace_cleanup'.

Signed-off-by: Ye Bin <yebin@huaweicloud.com>
---
kernel/trace/blktrace.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index f07a03c1e052..030e5716661e 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -387,6 +387,7 @@ static int blk_trace_stop(struct blk_trace *bt)

static void blk_trace_cleanup(struct request_queue *q, struct blk_trace *bt)
{
+ blk_trace_stop(bt);
synchronize_rcu();
blk_trace_free(q, bt);
put_probe_ref();
@@ -401,8 +402,7 @@ static int __blk_trace_remove(struct request_queue *q)
if (!bt)
return -EINVAL;

- if (bt->trace_state != Blktrace_running)
- blk_trace_cleanup(q, bt);
+ blk_trace_cleanup(q, bt);

return 0;
}
--
2.31.1