scsi: sr: Do not leak information in ioctl

sr_ioctl.c uses this pattern:

  result = sr_do_ioctl(cd, &cgc);
  to-user = buffer[];
  kfree(buffer);
  return result;

Use of a buffer without checking leaks information. Check result and jump
over the use of buffer if there is an error.

  result = sr_do_ioctl(cd, &cgc);
  if (result)
    goto err;
  to-user = buffer[];
err:
  kfree(buffer);
  return result;

Additionally, initialize the buffer to zero.

This problem can be seen in the 2.4.0 kernel.

Link: https://lore.kernel.org/r/20220411174756.2418435-1-trix@redhat.com
Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/sr_ioctl.c

@@ -41,7 +41,7 @@ static int sr_read_tochdr(struct cdrom_device_info *cdi,
 	int result;
 	unsigned char *buffer;
 
-	buffer = kmalloc(32, GFP_KERNEL);
+	buffer = kzalloc(32, GFP_KERNEL);
 	if (!buffer)
 		return -ENOMEM;
 
@@ -55,10 +55,13 @@ static int sr_read_tochdr(struct cdrom_device_info *cdi,
 	cgc.data_direction = DMA_FROM_DEVICE;
 
 	result = sr_do_ioctl(cd, &cgc);
+	if (result)
+		goto err;
 
 	tochdr->cdth_trk0 = buffer[2];
 	tochdr->cdth_trk1 = buffer[3];
 
+err:
 	kfree(buffer);
 	return result;
 }
@@ -71,7 +74,7 @@ static int sr_read_tocentry(struct cdrom_device_info *cdi,
 	int result;
 	unsigned char *buffer;
 
-	buffer = kmalloc(32, GFP_KERNEL);
+	buffer = kzalloc(32, GFP_KERNEL);
 	if (!buffer)
 		return -ENOMEM;
 
@@ -86,6 +89,8 @@ static int sr_read_tocentry(struct cdrom_device_info *cdi,
 	cgc.data_direction = DMA_FROM_DEVICE;
 
 	result = sr_do_ioctl(cd, &cgc);
+	if (result)
+		goto err;
 
 	tocentry->cdte_ctrl = buffer[5] & 0xf;
 	tocentry->cdte_adr = buffer[5] >> 4;
@@ -98,6 +103,7 @@ static int sr_read_tocentry(struct cdrom_device_info *cdi,
 		tocentry->cdte_addr.lba = (((((buffer[8] << 8) + buffer[9]) << 8)
 			+ buffer[10]) << 8) + buffer[11];
 
+err:
 	kfree(buffer);
 	return result;
 }
@@ -384,7 +390,7 @@ int sr_get_mcn(struct cdrom_device_info *cdi, struct cdrom_mcn *mcn)
 {
 	Scsi_CD *cd = cdi->handle;
 	struct packet_command cgc;
-	char *buffer = kmalloc(32, GFP_KERNEL);
+	char *buffer = kzalloc(32, GFP_KERNEL);
 	int result;
 
 	if (!buffer)
@@ -400,10 +406,13 @@ int sr_get_mcn(struct cdrom_device_info *cdi, struct cdrom_mcn *mcn)
 	cgc.data_direction = DMA_FROM_DEVICE;
 	cgc.timeout = IOCTL_TIMEOUT;
 	result = sr_do_ioctl(cd, &cgc);
+	if (result)
+		goto err;
 
 	memcpy(mcn->medium_catalog_number, buffer + 9, 13);
 	mcn->medium_catalog_number[13] = 0;
 
+err:
 	kfree(buffer);
 	return result;
 }