path: root/block
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authorBenjamin Block <bblock@linux.vnet.ibm.com>2017-10-03 12:48:37 +0200
committerJens Axboe <axboe@kernel.dk>2017-10-04 08:35:04 -0600
commiteab40cf336065e8d765e006b81ff48c5c114b365 (patch)
treee89276e6fd228e785faeda85c6c0e1c4928db144 /block
parentblk-mq-debugfs: fix device sched directory for default scheduler (diff)
bsg-lib: fix use-after-free under memory-pressure
When under memory-pressure it is possible that the mempool which backs the 'struct request_queue' will make use of up to BLKDEV_MIN_RQ count emergency buffers - in case it can't get a regular allocation. These buffers are preallocated and once they are also used, they are re-supplied with old finished requests from the same request_queue (see mempool_free()). The bug is, when re-supplying the emergency pool, the old requests are not again ran through the callback mempool_t->alloc(), and thus also not through the callback bsg_init_rq(). Thus we skip initialization, and while the sense-buffer still should be good, scsi_request->cmd might have become to be an invalid pointer in the meantime. When the request is initialized in bsg.c, and the user's CDB is larger than BLK_MAX_CDB, bsg will replace it with a custom allocated buffer, which is freed when the user's command is finished, thus it dangles afterwards. When next a command is sent by the user that has a smaller/similar CDB as BLK_MAX_CDB, bsg will assume that scsi_request->cmd is backed by scsi_request->__cmd, will not make a custom allocation, and write into undefined memory. Fix this by splitting bsg_init_rq() into two functions: - bsg_init_rq() is changed to only do the allocation of the sense-buffer, which is used to back the bsg job's reply buffer. This pointer should never change during the lifetime of a scsi_request, so it doesn't need re-initialization. - bsg_initialize_rq() is a new function that makes use of 'struct request_queue's initialize_rq_fn callback (which was introduced in v4.12). This is always called before the request is given out via blk_get_request(). This function does the remaining initialization that was previously done in bsg_init_rq(), and will also do it when the request is taken from the emergency-pool of the backing mempool. Fixes: 50b4d485528d ("bsg-lib: fix kernel panic resulting from missing allocation of reply-buffer") Cc: <stable@vger.kernel.org> # 4.11+ Reviewed-by: Hannes Reinecke <hare@suse.com> Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Benjamin Block <bblock@linux.vnet.ibm.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block')
1 files changed, 21 insertions, 6 deletions
diff --git a/block/bsg-lib.c b/block/bsg-lib.c
index dbddff8174e5..15d25ccd51a5 100644
--- a/block/bsg-lib.c
+++ b/block/bsg-lib.c
@@ -207,20 +207,34 @@ static int bsg_init_rq(struct request_queue *q, struct request *req, gfp_t gfp)
struct bsg_job *job = blk_mq_rq_to_pdu(req);
struct scsi_request *sreq = &job->sreq;
+ /* called right after the request is allocated for the request_queue */
+ sreq->sense = kzalloc(SCSI_SENSE_BUFFERSIZE, gfp);
+ if (!sreq->sense)
+ return -ENOMEM;
+ return 0;
+static void bsg_initialize_rq(struct request *req)
+ struct bsg_job *job = blk_mq_rq_to_pdu(req);
+ struct scsi_request *sreq = &job->sreq;
+ void *sense = sreq->sense;
+ /* called right before the request is given to the request_queue user */
memset(job, 0, sizeof(*job));
+ sreq->sense = sense;
sreq->sense_len = SCSI_SENSE_BUFFERSIZE;
- sreq->sense = kzalloc(sreq->sense_len, gfp);
- if (!sreq->sense)
- return -ENOMEM;
job->req = req;
- job->reply = sreq->sense;
+ job->reply = sense;
job->reply_len = sreq->sense_len;
job->dd_data = job + 1;
- return 0;
static void bsg_exit_rq(struct request_queue *q, struct request *req)
@@ -251,6 +265,7 @@ struct request_queue *bsg_setup_queue(struct device *dev, const char *name,
q->cmd_size = sizeof(struct bsg_job) + dd_job_size;
q->init_rq_fn = bsg_init_rq;
q->exit_rq_fn = bsg_exit_rq;
+ q->initialize_rq_fn = bsg_initialize_rq;
q->request_fn = bsg_request_fn;
ret = blk_init_allocated_queue(q);