[PATCH 3.12 47/84] iwlwifi: pcie: fix access to scratch buffer

[Jiri Slaby]

From: Sara Sharon <sara.sharon@xxxxxxxxx>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit d5d0689aefc59c6a5352ca25d7e6d47d03f543ce upstream.

This fixes a pretty ancient bug that hasn't manifested itself
until now.
The scratchbuf for command queue is allocated only for 32 slots
but is accessed with the queue write pointer - which can be
up to 256.
Since the scratch buf size was 16 and there are up to 256 TFDs
we never passed a page boundary when accessing the scratch buffer,
but when attempting to increase the size of the scratch buffer a
panic was quick to follow when trying to access the address resulted
in a page boundary.

Signed-off-by: Sara Sharon <sara.sharon@xxxxxxxxx>
Fixes: 38c0f334b359 ("iwlwifi: use coherent DMA memory for command header")
Signed-off-by: Luca Coelho <luciano.coelho@xxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
 drivers/net/wireless/iwlwifi/pcie/tx.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wireless/iwlwifi/pcie/tx.c b/drivers/net/wireless/iwlwifi/pcie/tx.c
index 911a15074ffb..6c769009587b 100644
--- a/drivers/net/wireless/iwlwifi/pcie/tx.c
+++ b/drivers/net/wireless/iwlwifi/pcie/tx.c
@@ -1328,9 +1328,9 @@ static int iwl_pcie_enqueue_hcmd(struct iwl_trans *trans,
 
 	/* start the TFD with the scratchbuf */
 	scratch_size = min_t(int, copy_size, IWL_HCMD_SCRATCHBUF_SIZE);
-	memcpy(&txq->scratchbufs[q->write_ptr], &out_cmd->hdr, scratch_size);
+	memcpy(&txq->scratchbufs[idx], &out_cmd->hdr, scratch_size);
 	iwl_pcie_txq_build_tfd(trans, txq,
-			       iwl_pcie_get_scratchbuf_dma(txq, q->write_ptr),
+			       iwl_pcie_get_scratchbuf_dma(txq, idx),
 			       scratch_size, 1);
 
 	/* map first command fragment, if any remains */
-- 
2.10.1