From: yu kuai yukuai3@huawei.com
hulk inclusion category: bugfix bugzilla: 30213 CVE: CVE-2019-19770
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syzbot is reporting use after free bug in debugfs_remove[1].
This is because in request_queue, 'q->debugfs_dir' and 'q->blk_trace->dir' could be the same dir. And in __blk_release_queue(), blk_mq_debugfs_unregister() will remove everything inside the dir.
With futher investigation of the reporduce repro, the problem can be reporduced by following procedure:
1. LOOP_CTL_ADD, create a request_queue q1, blk_mq_debugfs_register() will create the dir. 2. LOOP_CTL_REMOVE, blk_release_queue() will add q1 to release queue. 3. LOOP_CTL_ADD, create another request_queue q2,blk_mq_debugfs_register() will fail because the dir aready exist. 4. BLKTRACESETUP, create two files(msg and dropped) inside the dir. 5. call __blk_release_queue() for q1, debugfs_remove_recursive() will delete the files created in step 4. 6. LOOP_CTL_REMOVE, blk_release_queue() will add q2 to release queue. And when __blk_release_queue() is called for q2, blk_trace_shutdown() will try to release the two files created in step 4, wich are aready released in step 5.
thread1 |kworker |thread2 ----------------------- | ------------------------ | -------------------- loop_control_ioctl | | loop_add | | blk_mq_debugfs_register| | debugfs_create_dir | | loop_control_ioctl | | loop_remove | | blk_release_queue | | schedule_work | | | |loop_control_ioctl | | loop_add | | ... | |blk_trace_ioctl | | __blk_trace_setup | | debugfs_create_file |__blk_release_queue | | blk_mq_debugfs_unregister| | debugfs_remove_recursive| | |loop_control_ioctl | | loop_remove | | ... |__blk_release_queue | | blk_trace_shutdown | | debugfs_remove |
commit dc9edc44de6c ("block: Fix a blk_exit_rl() regression") pushed the final release of request_queue to a workqueue, so, when loop_add() is called again(step 3), __blk_release_queue() might not been called yet, which causes the problem.
Fix the problem by renaming 'q->debugfs_dir' or 'q->blk_trace->dir' in blk_unregister_queue() if they exist.
[1] https://syzkaller.appspot.com/bug?extid=903b72a010ad6b7a40f2 References: CVE-2019-19770 Fixes: commit dc9edc44de6c ("block: Fix a blk_exit_rl() regression") Reported-by: syzbot syz...@syzkaller.appspotmail.com Signed-off-by: yu kuai yukuai3@huawei.com Reviewed-by: Jason Yan yanaijie@huawei.com Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- block/blk-sysfs.c | 44 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 44 insertions(+)
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index 8286640..d249d7f 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -11,6 +11,7 @@ #include <linux/blktrace_api.h> #include <linux/blk-mq.h> #include <linux/blk-cgroup.h> +#include <linux/debugfs.h>
#include "blk.h" #include "blk-mq.h" @@ -958,6 +959,48 @@ int blk_register_queue(struct gendisk *disk) } EXPORT_SYMBOL_GPL(blk_register_queue);
+#ifdef CONFIG_DEBUG_FS +/* + * blk_prepare_release_queue - rename q->debugfs_dir and q->blk_trace->dir + * @q: request_queue of which the dir to be renamed belong to. + * + * Because the final release of request_queue is in a workqueue, the + * cleanup might not been finished yet while the same device start to + * create. It's not correct if q->debugfs_dir still exist while trying + * to create a new one. + */ +static void blk_prepare_release_queue(struct request_queue *q) +{ + struct dentry *new = NULL; + struct dentry **old = NULL; + char name[DNAME_INLINE_LEN]; + int i = 0; + +#ifdef CONFIG_BLK_DEBUG_FS + if (!IS_ERR_OR_NULL(q->debugfs_dir)) + old = &q->debugfs_dir; +#endif +#ifdef CONFIG_BLK_DEV_IO_TRACE + /* q->debugfs_dir and q->blk_trace->dir can't both exist */ + if (q->blk_trace && !IS_ERR_OR_NULL(q->blk_trace->dir)) + old = &q->blk_trace->dir; +#endif + if (old == NULL) + return; +#define MAX_ATTEMPT 1024 + while (new == NULL && i < MAX_ATTEMPT) { + sprintf(name, "ready_to_remove_%s_%d", + kobject_name(q->kobj.parent), i++); + new = debugfs_rename(blk_debugfs_root, *old, + blk_debugfs_root, name); + } + if (new) + *old = new; +} +#else +#define blk_prepare_release_queue(q) do { } while (0) +#endif + /** * blk_unregister_queue - counterpart of blk_register_queue() * @disk: Disk of which the request queue should be unregistered from sysfs. @@ -982,6 +1025,7 @@ void blk_unregister_queue(struct gendisk *disk) * concurrent elv_iosched_store() calls. */ mutex_lock(&q->sysfs_lock); + blk_prepare_release_queue(q);
blk_queue_flag_clear(QUEUE_FLAG_REGISTERED, q);