linux-kernel - [PATCH v2] selftests/x86/lam: Zero out buffer for readlink()

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Date:   Mon, 16 Oct 2023 14:24:46 +0800
From:   Binbin Wu <binbin.wu@...ux.intel.com>
To:     dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org,
        shuah@...nel.org
Cc:     linux-kselftest@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, kirill.shutemov@...ux.intel.com,
        binbin.wu@...ux.intel.com
Subject: [PATCH v2] selftests/x86/lam: Zero out buffer for readlink()

Zero out the buffer for readlink() since readlink() does not append a
terminating null byte to the buffer.  Also change the buffer length
passed to readlink() to 'PATH_MAX - 1' to ensure the resulting string
is always null terminated.

Fixes: 833c12ce0f430 ("selftests/x86/lam: Add inherit test cases for linear-address masking")

Signed-off-by: Binbin Wu <binbin.wu@...ux.intel.com>
---
v1->v2:
- Change the buffer length passed to readlink() to 'PATH_MAX - 1' to ensure the
  resulting string is always null terminated. [Kirill]

 tools/testing/selftests/x86/lam.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/x86/lam.c b/tools/testing/selftests/x86/lam.c
index eb0e46905bf9..8f9b06d9ce03 100644
--- a/tools/testing/selftests/x86/lam.c
+++ b/tools/testing/selftests/x86/lam.c
@@ -573,7 +573,7 @@ int do_uring(unsigned long lam)
 	char path[PATH_MAX] = {0};
 
 	/* get current process path */
-	if (readlink("/proc/self/exe", path, PATH_MAX) <= 0)
+	if (readlink("/proc/self/exe", path, PATH_MAX - 1) <= 0)
 		return 1;
 
 	int file_fd = open(path, O_RDONLY);
@@ -680,14 +680,14 @@ static int handle_execve(struct testcases *test)
 		perror("Fork failed.");
 		ret = 1;
 	} else if (pid == 0) {
-		char path[PATH_MAX];
+		char path[PATH_MAX] = {0};
 
 		/* Set LAM mode in parent process */
 		if (set_lam(lam) != 0)
 			return 1;
 
 		/* Get current binary's path and the binary was run by execve */
-		if (readlink("/proc/self/exe", path, PATH_MAX) <= 0)
+		if (readlink("/proc/self/exe", path, PATH_MAX - 1) <= 0)
 			exit(-1);
 
 		/* run binary to get LAM mode and return to parent process */

base-commit: 58720809f52779dc0f08e53e54b014209d13eebb
-- 
2.25.1