[PATCH] scsi: ses: Fix out-of-bound memory write

[Xunlei Pang <xlpang@linux.alibaba.com>]

Our memory debug tool captured the following exception:

  BUG: memory corruption in ses_enclosure_data_process+0x24b/0x310 [ses]
  ses_enclosure_data_process+0x24b/0x310 [ses]
  ses_intf_add+0x444/0x542 [ses]
  class_interface_register+0x110/0x120
  ses_init+0x13/0x1000 [ses]
  do_one_initcall+0x41/0x1c0
  do_init_module+0x5c/0x260
  __do_sys_finit_module+0xb1/0x110
  do_syscall_64+0x2d/0x40
  entry_SYSCALL_64_after_hwframe+0x44/0xa9

The root cause is "desc_ptr[len] = '\0'" makes out-of-bound
memory write beyond "buf", so make it within the buffer size.

Reported-by: Qingming Su <qingming.su@linux.alibaba.com>
Signed-off-by: Xunlei Pang <xlpang@linux.alibaba.com>
---
 drivers/scsi/ses.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/ses.c b/drivers/scsi/ses.c
index c2afba2a5414..c1ac2e96d25d 100644
--- a/drivers/scsi/ses.c
+++ b/drivers/scsi/ses.c
@@ -544,11 +544,14 @@ static void ses_enclosure_data_process(struct enclosure_device *edev,
 			char *name = NULL;
 			struct enclosure_component *ecomp;
 
+			if (desc_ptr + 4 >= buf + page7_len)
+				desc_ptr = NULL;
+
 			if (desc_ptr) {
-				if (desc_ptr >= buf + page7_len) {
+				len = (desc_ptr[2] << 8) + desc_ptr[3];
+				if (desc_ptr + 4 + len >= buf + page7_len) {
 					desc_ptr = NULL;
 				} else {
-					len = (desc_ptr[2] << 8) + desc_ptr[3];
 					desc_ptr += 4;
 					/* Add trailing zero - pushes into
 					 * reserved space */
-- 
2.20.1.7.g153144c