On 10/03/2017 12:48 PM, Christoph Hellwig wrote:
> From: Benjamin Block <bblock@xxxxxxxxxxxxxxxxxx>
>
> 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@xxxxxxxxxxxxxxx> # 4.11+
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> Signed-off-by: Benjamin Block <bblock@xxxxxxxxxxxxxxxxxx>
> ---
> block/bsg-lib.c | 27 +++++++++++++++++++++------
> 1 file changed, 21 insertions(+), 6 deletions(-)
>
Reviewed-by: Hannes Reinecke <hare@xxxxxxxx>
Cheers,
Hannes
--
Dr. Hannes Reinecke Teamlead Storage & Networking
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