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@linux.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

On Mon, Oct 16, 2023 at 02:24:46PM +0800, Binbin Wu wrote:
> 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@linux.intel.com>

Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

On 10/16/23 02:47, kirill.shutemov@linux.intel.com wrote:
> On Mon, Oct 16, 2023 at 02:24:46PM +0800, Binbin Wu wrote:
>> 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@linux.intel.com>
> 
> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> 

Thank you. Applied to linux-kselftest next for Linux 6.7-rc1

thanks,
-- Shuah

The following commit has been merged into the x86/mm branch of tip:

Commit-ID:     29060633411a02f6f2dd9d5245919385d69d81f0
Gitweb:        https://git.kernel.org/tip/29060633411a02f6f2dd9d5245919385d69d81f0
Author:        Binbin Wu <binbin.wu@linux.intel.com>
AuthorDate:    Mon, 16 Oct 2023 14:24:46 +08:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Mon, 16 Oct 2023 11:39:57 +02:00

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@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Link: https://lore.kernel.org/r/20231016062446.695-1-binbin.wu@linux.intel.com
---
 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 eb0e469..8f9b06d 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 */