[PATCH v2] ata: dwc_460ex: Avoid potential NULL pointer dereference

[Aditya Pakki]

dma_async_tx_descriptor can contain a NULL variable and using
it in dmaengine_submit without checking can crash the process.
This patch avoids such a scenario.

Signed-off-by: Aditya Pakki <pakki...@umn.edu>

---
v1: Return error in case of failure to desc variable to avoid hang up.
---
 drivers/ata/sata_dwc_460ex.c | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/drivers/ata/sata_dwc_460ex.c b/drivers/ata/sata_dwc_460ex.c
index 6f142aa54f5f..63d922c624a4 100644
--- a/drivers/ata/sata_dwc_460ex.c
+++ b/drivers/ata/sata_dwc_460ex.c
@@ -185,7 +185,7 @@ enum {
 /*
  * Prototypes
  */
-static void sata_dwc_bmdma_start_by_tag(struct ata_queued_cmd *qc, u8 tag);
+static int sata_dwc_bmdma_start_by_tag(struct ata_queued_cmd *qc, u8 tag);
 static int sata_dwc_qc_complete(struct ata_port *ap, struct ata_queued_cmd *qc,
                                u32 check_status);
 static void sata_dwc_dma_xfer_complete(struct ata_port *ap, u32 check_status);
@@ -512,7 +512,7 @@ static irqreturn_t sata_dwc_isr(int irq, void *dev_instance)
        struct ata_queued_cmd *qc;
        unsigned long flags;
        u8 status, tag;
-       int handled, num_processed, port = 0;
+       int handled, num_processed, ret, port = 0;
        uint intpr, sactive, sactive2, tag_mask;
        struct sata_dwc_device_port *hsdevp;
        hsdev->sactive_issued = 0;
@@ -553,10 +553,11 @@ static irqreturn_t sata_dwc_isr(int irq, void 
*dev_instance)
                 * be completed.
                 */
                qc->ap->link.active_tag = tag;
-               sata_dwc_bmdma_start_by_tag(qc, tag);
-
-               handled = 1;
-               goto DONE;
+               ret = sata_dwc_bmdma_start_by_tag(qc, tag);
+               if (!ret) {
+                       handled = 1;
+                       goto DONE;
+               }
        }
        sata_dwc_scr_read(&ap->link, SCR_ACTIVE, &sactive);
        tag_mask = (hsdev->sactive_issued | sactive) ^ sactive;
@@ -1008,7 +1009,7 @@ static void sata_dwc_bmdma_setup(struct ata_queued_cmd 
*qc)
        sata_dwc_bmdma_setup_by_tag(qc, tag);
 }
 
-static void sata_dwc_bmdma_start_by_tag(struct ata_queued_cmd *qc, u8 tag)
+static int sata_dwc_bmdma_start_by_tag(struct ata_queued_cmd *qc, u8 tag)
 {
        int start_dma;
        u32 reg;
@@ -1018,6 +1019,9 @@ static void sata_dwc_bmdma_start_by_tag(struct 
ata_queued_cmd *qc, u8 tag)
        struct dma_async_tx_descriptor *desc = hsdevp->desc[tag];
        int dir = qc->dma_dir;
 
+       if (!desc)
+               return -ENOMEM;
+
        if (hsdevp->cmd_issued[tag] != SATA_DWC_CMD_ISSUED_NOT) {
                start_dma = 1;
                if (dir == DMA_TO_DEVICE)
@@ -1055,9 +1059,10 @@ static void sata_dwc_bmdma_start_by_tag(struct 
ata_queued_cmd *qc, u8 tag)
                dmaengine_submit(desc);
                dma_async_issue_pending(hsdevp->chan);
        }
+       return 0;
 }
 
-static void sata_dwc_bmdma_start(struct ata_queued_cmd *qc)
+static int sata_dwc_bmdma_start(struct ata_queued_cmd *qc)
 {
        u8 tag = qc->hw_tag;
 
@@ -1068,7 +1073,7 @@ static void sata_dwc_bmdma_start(struct ata_queued_cmd 
*qc)
                tag = 0;
        }
        dev_dbg(qc->ap->dev, "%s\n", __func__);
-       sata_dwc_bmdma_start_by_tag(qc, tag);
+       return sata_dwc_bmdma_start_by_tag(qc, tag);
 }
 
 static unsigned int sata_dwc_qc_issue(struct ata_queued_cmd *qc)
-- 
2.17.1