mmc: sdhci: fix NULL dereference in sdhci_request() tuning

Commit 473b095a72a9 ("mmc: sdhci: fix incorrect command used in tuning")
introduced a NULL dereference at resume-time if an SD 3.0 host controller
raises the SDHCI_NEEDS_TUNING flag while no card is inserted.  Seen on an
OLPC XO-4 with sdhci-pxav3, but presumably affects other controllers too.

Signed-off-by: Chris Ball <cjb@laptop.org>
Cc: stable <stable@vger.kernel.org> [3.3+]

1 files changed, 13 insertions, 10 deletions

diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
index 949e18c7c05d..c7851c0aabce 100644
--- a/drivers/mmc/host/sdhci.c
+++ b/drivers/mmc/host/sdhci.c
@@ -1315,16 +1315,19 @@ static void sdhci_request(struct mmc_host *mmc, struct mmc_request *mrq)
                  */
                 if ((host->flags & SDHCI_NEEDS_RETUNING) &&
                     !(present_state & (SDHCI_DOING_WRITE | SDHCI_DOING_READ))) {
-                        /* eMMC uses cmd21 while sd and sdio use cmd19 */
-                        tuning_opcode = mmc->card->type == MMC_TYPE_MMC ?
-                                MMC_SEND_TUNING_BLOCK_HS200 :
-                                MMC_SEND_TUNING_BLOCK;
-                        spin_unlock_irqrestore(&host->lock, flags);
-                        sdhci_execute_tuning(mmc, tuning_opcode);
-                        spin_lock_irqsave(&host->lock, flags);
-
-                        /* Restore original mmc_request structure */
-                        host->mrq = mrq;
+                        if (mmc->card) {
+                                /* eMMC uses cmd21 but sd and sdio use cmd19 */
+                                tuning_opcode =
+                                        mmc->card->type == MMC_TYPE_MMC ?
+                                        MMC_SEND_TUNING_BLOCK_HS200 :
+                                        MMC_SEND_TUNING_BLOCK;
+                                spin_unlock_irqrestore(&host->lock, flags);
+                                sdhci_execute_tuning(mmc, tuning_opcode);
+                                spin_lock_irqsave(&host->lock, flags);
+
+                                /* Restore original mmc_request structure */
+                                host->mrq = mrq;
+                        }
                 }
 
                 if (mrq->sbc && !(host->flags & SDHCI_AUTO_CMD23))