linux-kernel - [PATCH v3 12/14] selftests/nolibc: prevent out of bounds access in expect

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Message-Id: <20230803-nolibc-warnings-v3-12-bcc1a096ae02@weissschuh.net>
Date:   Thu, 03 Aug 2023 09:28:56 +0200
From:   Thomas Weißschuh <linux@...ssschuh.net>
To:     Willy Tarreau <w@....eu>, Shuah Khan <shuah@...nel.org>
Cc:     linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        Yuan Tan <tanyuan@...ylab.org>,
        Zhangjin Wu <falcon@...ylab.org>,
        Thomas Weißschuh <linux@...ssschuh.net>
Subject: [PATCH v3 12/14] selftests/nolibc: prevent out of bounds access in
 expect_vfprintf

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@...ssschuh.net>
---
 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 63f09800057d..0145a44af990 100644
--- a/tools/testing/selftests/nolibc/nolibc-test.c
+++ b/tools/testing/selftests/nolibc/nolibc-test.c
@@ -1055,7 +1055,6 @@ static int expect_vfprintf(int llen, int c, const char *expected, const char *fm
 	lseek(fd, 0, SEEK_SET);
 
 	r = read(fd, buf, sizeof(buf) - 1);
-	buf[r] = '\0';
 
 	fclose(memfile);
 
@@ -1065,6 +1064,7 @@ static int expect_vfprintf(int llen, int c, const char *expected, const char *fm
 		return 1;
 	}
 
+	buf[r] = '\0';
 	llen += printf(" \"%s\" = \"%s\"", expected, buf);
 	ret = strncmp(expected, buf, c);
 

-- 
2.41.0