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| author | Cengiz Can <cengiz@kernel.wtf> | 2020-03-04 13:58:19 +0300 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2020-03-05 13:42:40 -0700 |
| commit | 153031a301bb07194e9c37466cfce8eacb977621 (patch) | |
| tree | bf8ca84dffca3ce7c7b53ea4f4334484d6b3800d /kernel | |
| parent | 764b53b26c9897b0693c934797e898d6cd883a26 (diff) | |
| download | lwn-153031a301bb07194e9c37466cfce8eacb977621.tar.gz lwn-153031a301bb07194e9c37466cfce8eacb977621.zip | |
blktrace: fix dereference after null check
There was a recent change in blktrace.c that added a RCU protection to
`q->blk_trace` in order to fix a use-after-free issue during access.
However the change missed an edge case that can lead to dereferencing of
`bt` pointer even when it's NULL:
Coverity static analyzer marked this as a FORWARD_NULL issue with CID
1460458.
```
/kernel/trace/blktrace.c: 1904 in sysfs_blk_trace_attr_store()
1898 ret = 0;
1899 if (bt == NULL)
1900 ret = blk_trace_setup_queue(q, bdev);
1901
1902 if (ret == 0) {
1903 if (attr == &dev_attr_act_mask)
>>> CID 1460458: Null pointer dereferences (FORWARD_NULL)
>>> Dereferencing null pointer "bt".
1904 bt->act_mask = value;
1905 else if (attr == &dev_attr_pid)
1906 bt->pid = value;
1907 else if (attr == &dev_attr_start_lba)
1908 bt->start_lba = value;
1909 else if (attr == &dev_attr_end_lba)
```
Added a reassignment with RCU annotation to fix the issue.
Fixes: c780e86dd48 ("blktrace: Protect q->blk_trace with RCU")
Cc: stable@vger.kernel.org
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Bob Liu <bob.liu@oracle.com>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Cengiz Can <cengiz@kernel.wtf>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/trace/blktrace.c | 5 |
1 files changed, 4 insertions, 1 deletions
diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c index 4560878f0bac..ca39dc3230cb 100644 --- a/kernel/trace/blktrace.c +++ b/kernel/trace/blktrace.c @@ -1896,8 +1896,11 @@ static ssize_t sysfs_blk_trace_attr_store(struct device *dev, } ret = 0; - if (bt == NULL) + if (bt == NULL) { ret = blk_trace_setup_queue(q, bdev); + bt = rcu_dereference_protected(q->blk_trace, + lockdep_is_held(&q->blk_trace_mutex)); + } if (ret == 0) { if (attr == &dev_attr_act_mask) |