target: Fix possible integer underflow in UNMAP emulation

It's possible for an initiator to send us an UNMAP command with a
descriptor that is less than 8 bytes; in that case it's really bad for
us to set an unsigned int to that value, subtract 8 from it, and then
use that as a limit for our loop (since the value will wrap around to
a huge positive value).

Fix this by making size be signed and only looping if size >= 16 (ie
if we have at least a full descriptor available).

Also remove offset as an obfuscated name for the constant 8.

Signed-off-by: Roland Dreier <roland@purestorage.com>
Cc: stable@vger.kernel.org
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

diff --git a/drivers/target/target_core_iblock.c b/drivers/target/target_core_iblock.c
index e6d08ee..2efd70c 100644 (file)
--- a/drivers/target/target_core_iblock.c
+++ b/drivers/target/target_core_iblock.c
@@ -325,24 +325,24 @@ static int iblock_execute_unmap(struct se_cmd *cmd)
        struct iblock_dev *ibd = dev->dev_ptr;
        unsigned char *buf, *ptr = NULL;
        sector_t lba;
-       unsigned int size = cmd->data_length, range;
-       int ret = 0, offset;
-       unsigned short dl, bd_dl;
-
-       /* First UNMAP block descriptor starts at 8 byte offset */
-       offset = 8;
-       size -= 8;
+       int size = cmd->data_length;
+       u32 range;
+       int ret = 0;
+       int dl, bd_dl;
 
        buf = transport_kmap_data_sg(cmd);
 
        dl = get_unaligned_be16(&buf[0]);
        bd_dl = get_unaligned_be16(&buf[2]);
 
-       ptr = &buf[offset];
-       pr_debug("UNMAP: Sub: %s Using dl: %hu bd_dl: %hu size: %hu"
+       size = min(size - 8, bd_dl);
+
+       /* First UNMAP block descriptor starts at 8 byte offset */
+       ptr = &buf[8];
+       pr_debug("UNMAP: Sub: %s Using dl: %u bd_dl: %u size: %u"
                " ptr: %p\n", dev->transport->name, dl, bd_dl, size, ptr);
 
-       while (size) {
+       while (size >= 16) {
                lba = get_unaligned_be64(&ptr[0]);
                range = get_unaligned_be32(&ptr[8]);
                pr_debug("UNMAP: Using lba: %llu and range: %u\n",