[PATCH 6/6] scsi: Check sense buffer size at build time

[Kees Cook <keescook@chromium.org>]

To avoid introducing problems like those fixed in commit f7068114d45e
("sr: pass down correctly sized SCSI sense buffer"), this creates a macro
wrapper for scsi_execute() that verifies the size of the sense buffer
similar to what was done for command string sizes in commit 3756f6401c30
("exec: avoid gcc-8 warning for get_task_comm").

Another solution could be to add another argument to scsi_execute(),
but this function already takes a lot of arguments and Jens was not fond
of that approach. As there was only a pair of dynamically allocated sense
buffers, this also moves those 96 bytes onto the stack to avoid triggering
the sizeof() check.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 drivers/scsi/scsi_lib.c    |  6 +++---
 include/scsi/scsi_device.h | 12 +++++++++++-
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index e9b4f279d29c..718c2bec4516 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -238,7 +238,7 @@ void scsi_queue_insert(struct scsi_cmnd *cmd, int reason)
 
 
 /**
- * scsi_execute - insert request and wait for the result
+ * __scsi_execute - insert request and wait for the result
  * @sdev:	scsi device
  * @cmd:	scsi command
  * @data_direction: data direction
@@ -255,7 +255,7 @@ void scsi_queue_insert(struct scsi_cmnd *cmd, int reason)
  * Returns the scsi_cmnd result field if a command was executed, or a negative
  * Linux error code if we didn't get that far.
  */
-int scsi_execute(struct scsi_device *sdev, const unsigned char *cmd,
+int __scsi_execute(struct scsi_device *sdev, const unsigned char *cmd,
 		 int data_direction, void *buffer, unsigned bufflen,
 		 unsigned char *sense, struct scsi_sense_hdr *sshdr,
 		 int timeout, int retries, u64 flags, req_flags_t rq_flags,
@@ -309,7 +309,7 @@ int scsi_execute(struct scsi_device *sdev, const unsigned char *cmd,
 
 	return ret;
 }
-EXPORT_SYMBOL(scsi_execute);
+EXPORT_SYMBOL(__scsi_execute);
 
 /*
  * Function:    scsi_init_cmd_errh()
diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index 7ae177c8e399..1bb87b6c0ad2 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -426,11 +426,21 @@ extern const char *scsi_device_state_name(enum scsi_device_state);
 extern int scsi_is_sdev_device(const struct device *);
 extern int scsi_is_target_device(const struct device *);
 extern void scsi_sanitize_inquiry_string(unsigned char *s, int len);
-extern int scsi_execute(struct scsi_device *sdev, const unsigned char *cmd,
+extern int __scsi_execute(struct scsi_device *sdev, const unsigned char *cmd,
 			int data_direction, void *buffer, unsigned bufflen,
 			unsigned char *sense, struct scsi_sense_hdr *sshdr,
 			int timeout, int retries, u64 flags,
 			req_flags_t rq_flags, int *resid);
+/* Make sure any sense buffer is the correct size. */
+#define scsi_execute(sdev, cmd, data_direction, buffer, bufflen, sense,	\
+		     sshdr, timeout, retries, flags, rq_flags, resid)	\
+({									\
+	BUILD_BUG_ON((sense) != NULL &&					\
+		     sizeof(sense) != SCSI_SENSE_BUFFERSIZE);		\
+	__scsi_execute(sdev, cmd, data_direction, buffer, bufflen,	\
+		       sense, sshdr, timeout, retries, flags, rq_flags,	\
+		       resid);						\
+})
 static inline int scsi_execute_req(struct scsi_device *sdev,
 	const unsigned char *cmd, int data_direction, void *buffer,
 	unsigned bufflen, struct scsi_sense_hdr *sshdr, int timeout,
-- 
2.17.0