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Subject[ 67/82] target: Fix possible integer underflow in UNMAP emulation
Date
From: Greg KH <gregkh@linuxfoundation.org>

3.5-stable review patch. If anyone has any objections, please let me know.

------------------

From: Roland Dreier <roland@purestorage.com>

commit b7fc7f3777582dea85156a821d78a522a0c083aa upstream.

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>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
[bwh: Backported to 3.2: adjust filename, context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/target/target_core_cdb.c | 20 ++++++++++----------
1 file changed, 10 insertions(+), 10 deletions(-)

--- a/drivers/target/target_core_cdb.c
+++ b/drivers/target/target_core_cdb.c
@@ -1014,9 +1014,10 @@ int target_emulate_unmap(struct se_cmd *
struct se_device *dev = cmd->se_dev;
unsigned char *buf, *ptr = NULL;
sector_t lba;
- unsigned int size = cmd->data_length, range;
- int ret = 0, offset;
- unsigned short dl, bd_dl;
+ int size = cmd->data_length;
+ u32 range;
+ int ret = 0;
+ int dl, bd_dl;

if (!dev->transport->do_discard) {
pr_err("UNMAP emulation not supported for: %s\n",
@@ -1025,20 +1026,19 @@ int target_emulate_unmap(struct se_cmd *
return -ENOSYS;
}

- /* First UNMAP block descriptor starts at 8 byte offset */
- offset = 8;
- size -= 8;
-
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",



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