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Subject[210/264] tcm_loop: Add explict read buffer memset for SCF_SCSI_CONTROL_SG_IO_CDB
3.1-stable review patch.  If anyone has any objections, please let me know.

------------------
From: Nicholas Bellinger <nab@linux-iscsi.org>

commit 8cd79f24350826b81e16990d9e12bc878e67d385 upstream.

This patch addresses an issue with buggy userspace code sending I/O
via scsi-generic that does not explictly clear their associated read
buffers. It adds an explict memset of the first SGL entry within
tcm_loop_new_cmd_map() for SCF_SCSI_CONTROL_SG_IO_CDB payloads that
are currently guaranteed to be a single SGL by target-core code.

This issue is a side effect of the v3.1-rc1 merge to remove the
extra memcpy between certain control CDB types using a contigious
+ cleared buffer in target-core, and performing a memcpy into the
SGL list within tcm_loop.

It was originally mainfesting itself by udev + scsi_id + scsi-generic
not properly setting up the expected /dev/disk/by-id/ symlinks because
the INQUIRY payload was containing extra bogus data preventing the
proper NAA IEEE WWN from being parsed by userspace.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Andy Grover <agrover@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
drivers/target/loopback/tcm_loop.c | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
--- a/drivers/target/loopback/tcm_loop.c
+++ b/drivers/target/loopback/tcm_loop.c
@@ -174,6 +174,24 @@ static int tcm_loop_new_cmd_map(struct s
sgl_bidi = sdb->table.sgl;
sgl_bidi_count = sdb->table.nents;
}
+ /*
+ * Because some userspace code via scsi-generic do not memset their
+ * associated read buffers, go ahead and do that here for type
+ * SCF_SCSI_CONTROL_SG_IO_CDB. Also note that this is currently
+ * guaranteed to be a single SGL for SCF_SCSI_CONTROL_SG_IO_CDB
+ * by target core in transport_generic_allocate_tasks() ->
+ * transport_generic_cmd_sequencer().
+ */
+ if (se_cmd->se_cmd_flags & SCF_SCSI_CONTROL_SG_IO_CDB &&
+ se_cmd->data_direction == DMA_FROM_DEVICE) {
+ struct scatterlist *sg = scsi_sglist(sc);
+ unsigned char *buf = kmap(sg_page(sg)) + sg->offset;
+
+ if (buf != NULL) {
+ memset(buf, 0, sg->length);
+ kunmap(sg_page(sg));
+ }
+ }

/* Tell the core about our preallocated memory */
ret = transport_generic_map_mem_to_cmd(se_cmd, scsi_sglist(sc),



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