mmc: check find_mmc_device return value

find_mmc_device returns NULL if an invalid device number is specified.
Check for this to avoid dereferencing NULL pointers.

Signed-off-by: Rabin Vincent <rabin@rab.in>

common/cmd_mmc.c

@@ -149,6 +149,9 @@ int do_mmcops(cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
 			int dev = simple_strtoul(argv[2], NULL, 10);
 			struct mmc *mmc = find_mmc_device(dev);
 
+			if (!mmc)
+				return 1;
+
 			mmc_init(mmc);
 
 			return 0;
@@ -175,6 +178,9 @@ int do_mmcops(cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
 			u32 blk = simple_strtoul(argv[4], NULL, 16);
 			struct mmc *mmc = find_mmc_device(dev);
 
+			if (!mmc)
+				return 1;
+
 			printf("\nMMC read: dev # %d, block # %d, count %d ... ",
 				dev, blk, cnt);
 
@@ -197,6 +203,9 @@ int do_mmcops(cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
 
 			int blk = simple_strtoul(argv[4], NULL, 16);
 
+			if (!mmc)
+				return 1;
+
 			printf("\nMMC write: dev # %d, block # %d, count %d ... ",
 				dev, blk, cnt);
 

drivers/mmc/mmc.c

@@ -846,7 +846,7 @@ block_dev_desc_t *mmc_get_dev(int dev)
 {
 	struct mmc *mmc = find_mmc_device(dev);
 
-	return &mmc->block_dev;
+	return mmc ? &mmc->block_dev : NULL;
 }
 
 int mmc_init(struct mmc *mmc)