[RFC v4 5/7] mm: Fix benign off-by-one bugs

[Alejandro Colomar]

We were wasting a byte due to an off-by-one bug.  s[c]nprintf()
doesn't write more than $2 bytes including the null byte, so trying to
pass 'size-1' there is wasting one byte.  Now that we use seprintf(),
the situation isn't different: seprintf() will stop writing *before*
'end' --that is, at most the terminating null byte will be written at
'end-1'--.

Acked-by: Marco Elver <elver@xxxxxxxxxx>
Cc: Kees Cook <kees@xxxxxxxxxx>
Cc: Christopher Bazley <chris.bazley.wg14@xxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Cc: Marco Elver <elver@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Alejandro Colomar <alx@xxxxxxxxxx>
---
 mm/kfence/kfence_test.c | 4 ++--
 mm/kmsan/kmsan_test.c   | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/kfence/kfence_test.c b/mm/kfence/kfence_test.c
index bae382eca4ab..c635aa9d478b 100644
--- a/mm/kfence/kfence_test.c
+++ b/mm/kfence/kfence_test.c
@@ -110,7 +110,7 @@ static bool report_matches(const struct expect_report *r)
 
 	/* Title */
 	cur = expect[0];
-	end = &expect[0][sizeof(expect[0]) - 1];
+	end = ENDOF(expect[0]);
 	switch (r->type) {
 	case KFENCE_ERROR_OOB:
 		cur = sprintf_end(cur, end, "BUG: KFENCE: out-of-bounds %s",
@@ -140,7 +140,7 @@ static bool report_matches(const struct expect_report *r)
 
 	/* Access information */
 	cur = expect[1];
-	end = &expect[1][sizeof(expect[1]) - 1];
+	end = ENDOF(expect[1]);
 
 	switch (r->type) {
 	case KFENCE_ERROR_OOB:
diff --git a/mm/kmsan/kmsan_test.c b/mm/kmsan/kmsan_test.c
index e48ca1972ff3..9bda55992e3d 100644
--- a/mm/kmsan/kmsan_test.c
+++ b/mm/kmsan/kmsan_test.c
@@ -105,7 +105,7 @@ static bool report_matches(const struct expect_report *r)
 
 	/* Title */
 	cur = expected_header;
-	end = &expected_header[sizeof(expected_header) - 1];
+	end = ENDOF(expected_header);
 
 	cur = sprintf_end(cur, end, "BUG: KMSAN: %s", r->error_type);
 
-- 
2.50.0