[PATCH AUTOSEL 6.5 16/16] selftests/nolibc: prevent out of bounds access in expect_vfprintf

[Sasha Levin]

From: Thomas Weißschuh <linux@xxxxxxxxxxxxxx>

[ Upstream commit 9c5e490093e83e165022e0311bd7df5aa06cc860 ]

If read() fails and returns -1 (or returns garbage for some other
reason) buf would be accessed out of bounds.
Only use the return value of read() after it has been validated.

Signed-off-by: Thomas Weißschuh <linux@xxxxxxxxxxxxxx>
Signed-off-by: Willy Tarreau <w@xxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 tools/testing/selftests/nolibc/nolibc-test.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
index 55628a25df0a3..8e7750e2eb97c 100644
--- a/tools/testing/selftests/nolibc/nolibc-test.c
+++ b/tools/testing/selftests/nolibc/nolibc-test.c
@@ -769,7 +769,6 @@ static int expect_vfprintf(int llen, size_t c, const char *expected, const char
 	lseek(fd, 0, SEEK_SET);
 
 	r = read(fd, buf, sizeof(buf) - 1);
-	buf[r] = '\0';
 
 	fclose(memfile);
 
@@ -779,6 +778,7 @@ static int expect_vfprintf(int llen, size_t c, const char *expected, const char
 		return 1;
 	}
 
+	buf[r] = '\0';
 	llen += printf(" \"%s\" = \"%s\"", expected, buf);
 	ret = strncmp(expected, buf, c);
 
-- 
2.40.1