linux-kernel - [ 53/65] target: Fix possible integer underflow in UNMAP emulation

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Message-Id: <20120813221419.646367350@linuxfoundation.org>
Date:	Mon, 13 Aug 2012 15:14:37 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Roland Dreier <roland@...estorage.com>,
	Nicholas Bellinger <nab@...ux-iscsi.org>,
	Ben Hutchings <ben@...adent.org.uk>
Subject: [ 53/65] target: Fix possible integer underflow in UNMAP emulation

From: Greg KH <gregkh@...uxfoundation.org>

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

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

From: Roland Dreier <roland@...estorage.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@...estorage.com>
Signed-off-by: Nicholas Bellinger <nab@...ux-iscsi.org>
[bwh: Backported to 3.2: adjust filename, context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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
@@ -1023,9 +1023,10 @@ int target_emulate_unmap(struct se_task
 	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",
@@ -1034,20 +1035,19 @@ int target_emulate_unmap(struct se_task
 		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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