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[PATCH 4.9 069/171] elevator: fix truncation of icq_cache_name




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

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

[ Upstream commit 9bd2bbc01d17ddd567cc0f81f77fe1163e497462 ]

gcc 7.1 reports the following warning:

    block/elevator.c: In function ‘elv_register’:
    block/elevator.c:898:5: warning: ‘snprintf’ output may be truncated before the last format character [-Wformat-truncation=]
         "%s_io_cq", e->elevator_name);
         ^~~~~~~~~~
    block/elevator.c:897:3: note: ‘snprintf’ output between 7 and 22 bytes into a destination of size 21
       snprintf(e->icq_cache_name, sizeof(e->icq_cache_name),
       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
         "%s_io_cq", e->elevator_name);
         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The bug is that the name of the icq_cache is 6 characters longer than
the elevator name, but only ELV_NAME_MAX + 5 characters were reserved
for it --- so in the case of a maximum-length elevator name, the 'q'
character in "_io_cq" would be truncated by snprintf().  Fix it by
reserving ELV_NAME_MAX + 6 characters instead.

Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
Reviewed-by: Bart Van Assche <Bart.VanAssche@xxxxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 include/linux/elevator.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/elevator.h b/include/linux/elevator.h
index e7f358d2e5fc..eaa58c0f894b 100644
--- a/include/linux/elevator.h
+++ b/include/linux/elevator.h
@@ -102,7 +102,7 @@ struct elevator_type
 	struct module *elevator_owner;
 
 	/* managed by elevator core */
-	char icq_cache_name[ELV_NAME_MAX + 5];	/* elvname + "_io_cq" */
+	char icq_cache_name[ELV_NAME_MAX + 6];	/* elvname + "_io_cq" */
 	struct list_head list;
 };
 
-- 
2.17.1