mmc: core: check for zero length ioctl data

If the read or write buffer size associated with the command sent
through the mmc_blk_ioctl is zero, do not prepare data buffer.

This enables a ioctl(2) call to for instance send a MMC_SWITCH to set
a byte in the ext_csd.

Signed-off-by: Johan Rudholm <johan.rudholm@stericsson.com>
Signed-off-by: Chris Ball <cjb@laptop.org>

1 files changed, 45 insertions, 37 deletions

diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
index c80bb6de40b8..ad0fb8d74dda 100644
--- a/drivers/mmc/card/block.c
+++ b/drivers/mmc/card/block.c
@@ -266,6 +266,9 @@ static struct mmc_blk_ioc_data *mmc_blk_ioctl_copy_from_user(
                 goto idata_err;
         }
 
+        if (!idata->buf_bytes)
+                return idata;
+
         idata->buf = kzalloc(idata->buf_bytes, GFP_KERNEL);
         if (!idata->buf) {
                 err = -ENOMEM;
@@ -312,25 +315,6 @@ static int mmc_blk_ioctl_cmd(struct block_device *bdev,
         if (IS_ERR(idata))
                 return PTR_ERR(idata);
 
-        cmd.opcode = idata->ic.opcode;
-        cmd.arg = idata->ic.arg;
-        cmd.flags = idata->ic.flags;
-
-        data.sg = &sg;
-        data.sg_len = 1;
-        data.blksz = idata->ic.blksz;
-        data.blocks = idata->ic.blocks;
-
-        sg_init_one(data.sg, idata->buf, idata->buf_bytes);
-
-        if (idata->ic.write_flag)
-                data.flags = MMC_DATA_WRITE;
-        else
-                data.flags = MMC_DATA_READ;
-
-        mrq.cmd = &cmd;
-        mrq.data = &data;
-
         md = mmc_blk_get(bdev->bd_disk);
         if (!md) {
                 err = -EINVAL;
@@ -343,6 +327,48 @@ static int mmc_blk_ioctl_cmd(struct block_device *bdev,
                 goto cmd_done;
         }
 
+        cmd.opcode = idata->ic.opcode;
+        cmd.arg = idata->ic.arg;
+        cmd.flags = idata->ic.flags;
+
+        if (idata->buf_bytes) {
+                data.sg = &sg;
+                data.sg_len = 1;
+                data.blksz = idata->ic.blksz;
+                data.blocks = idata->ic.blocks;
+
+                sg_init_one(data.sg, idata->buf, idata->buf_bytes);
+
+                if (idata->ic.write_flag)
+                        data.flags = MMC_DATA_WRITE;
+                else
+                        data.flags = MMC_DATA_READ;
+
+                /* data.flags must already be set before doing this. */
+                mmc_set_data_timeout(&data, card);
+
+                /* Allow overriding the timeout_ns for empirical tuning. */
+                if (idata->ic.data_timeout_ns)
+                        data.timeout_ns = idata->ic.data_timeout_ns;
+
+                if ((cmd.flags & MMC_RSP_R1B) == MMC_RSP_R1B) {
+                        /*
+                         * Pretend this is a data transfer and rely on the
+                         * host driver to compute timeout.  When all host
+                         * drivers support cmd.cmd_timeout for R1B, this
+                         * can be changed to:
+                         *
+                         *     mrq.data = NULL;
+                         *     cmd.cmd_timeout = idata->ic.cmd_timeout_ms;
+                         */
+                        data.timeout_ns = idata->ic.cmd_timeout_ms * 1000000;
+                }
+
+                mrq.data = &data;
+        }
+
+        mrq.cmd = &cmd;
+
         mmc_claim_host(card->host);
 
         if (idata->ic.is_acmd) {
@@ -351,24 +377,6 @@ static int mmc_blk_ioctl_cmd(struct block_device *bdev,
                         goto cmd_rel_host;
         }
 
-        /* data.flags must already be set before doing this. */
-        mmc_set_data_timeout(&data, card);
-        /* Allow overriding the timeout_ns for empirical tuning. */
-        if (idata->ic.data_timeout_ns)
-                data.timeout_ns = idata->ic.data_timeout_ns;
-
-        if ((cmd.flags & MMC_RSP_R1B) == MMC_RSP_R1B) {
-                /*
-                 * Pretend this is a data transfer and rely on the host driver
-                 * to compute timeout.  When all host drivers support
-                 * cmd.cmd_timeout for R1B, this can be changed to:
-                 *
-                 *     mrq.data = NULL;
-                 *     cmd.cmd_timeout = idata->ic.cmd_timeout_ms;
-                 */
-                data.timeout_ns = idata->ic.cmd_timeout_ms * 1000000;
-        }
-
         mmc_wait_for_req(card->host, &mrq);
 
         if (cmd.error) {