[PATCH v2] selftests/exec: include cwd in long path calculation

[Steve Muckle <smuckle.linux@gmail.com>]

When creating a pathname close to PATH_MAX to test execveat, factor in
the current working directory path otherwise we end up with an absolute
path that is longer than PATH_MAX. While execveat() may succeed, subsequent
calls to the kernel from the runtime environment which are required to
successfully execute the test binary/script may fail because of this.

To keep the semantics of the test the same, rework the relative pathname
part of the test to be relative to the root directory so it isn't
decreased by the length of the current working directory path.

Signed-off-by: Steve Muckle <smuckle.linux@gmail.com>
---
Differences from v1:
 - free allocation from getcwd()
 - update comment in check_execveat_pathmax()

 tools/testing/selftests/exec/execveat.c | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

diff --git a/tools/testing/selftests/exec/execveat.c b/tools/testing/selftests/exec/execveat.c
index 8d5d1d2ee7c1..67cd4597db2b 100644
--- a/tools/testing/selftests/exec/execveat.c
+++ b/tools/testing/selftests/exec/execveat.c
@@ -147,7 +147,7 @@ static void exe_cp(const char *src, const char *dest)
 }
 
 #define XX_DIR_LEN 200
-static int check_execveat_pathmax(int dot_dfd, const char *src, int is_script)
+static int check_execveat_pathmax(int root_dfd, const char *src, int is_script)
 {
 	int fail = 0;
 	int ii, count, len;
@@ -156,20 +156,30 @@ static int check_execveat_pathmax(int dot_dfd, const char *src, int is_script)
 
 	if (*longpath == '\0') {
 		/* Create a filename close to PATH_MAX in length */
+		char *cwd = getcwd(NULL, 0);
+
+		if (!cwd) {
+			printf("Failed to getcwd(), errno=%d (%s)\n",
+			       errno, strerror(errno));
+			return 2;
+		}
+		strcpy(longpath, cwd);
+		strcat(longpath, "/");
 		memset(longname, 'x', XX_DIR_LEN - 1);
 		longname[XX_DIR_LEN - 1] = '/';
 		longname[XX_DIR_LEN] = '\0';
-		count = (PATH_MAX - 3) / XX_DIR_LEN;
+		count = (PATH_MAX - 3 - strlen(cwd)) / XX_DIR_LEN;
 		for (ii = 0; ii < count; ii++) {
 			strcat(longpath, longname);
 			mkdir(longpath, 0755);
 		}
-		len = (PATH_MAX - 3) - (count * XX_DIR_LEN);
+		len = (PATH_MAX - 3 - strlen(cwd)) - (count * XX_DIR_LEN);
 		if (len <= 0)
 			len = 1;
 		memset(longname, 'y', len);
 		longname[len] = '\0';
 		strcat(longpath, longname);
+		free(cwd);
 	}
 	exe_cp(src, longpath);
 
@@ -190,7 +200,7 @@ static int check_execveat_pathmax(int dot_dfd, const char *src, int is_script)
 	}
 
 	/*
-	 * Execute as a long pathname relative to ".".  If this is a script,
+	 * Execute as a long pathname relative to "/".  If this is a script,
 	 * the interpreter will launch but fail to open the script because its
 	 * name ("/dev/fd/5/xxx....") is bigger than PATH_MAX.
 	 *
@@ -200,10 +210,10 @@ static int check_execveat_pathmax(int dot_dfd, const char *src, int is_script)
 	 * the exit status shall be 126."), so allow either.
 	 */
 	if (is_script)
-		fail += check_execveat_invoked_rc(dot_dfd, longpath, 0,
+		fail += check_execveat_invoked_rc(root_dfd, longpath + 1, 0,
 						  127, 126);
 	else
-		fail += check_execveat(dot_dfd, longpath, 0);
+		fail += check_execveat(root_dfd, longpath + 1, 0);
 
 	return fail;
 }
@@ -218,6 +228,7 @@ static int run_tests(void)
 	int subdir_dfd_ephemeral = open_or_die("subdir.ephemeral",
 					       O_DIRECTORY|O_RDONLY);
 	int dot_dfd = open_or_die(".", O_DIRECTORY|O_RDONLY);
+	int root_dfd = open_or_die("/", O_DIRECTORY|O_RDONLY);
 	int dot_dfd_path = open_or_die(".", O_DIRECTORY|O_RDONLY|O_PATH);
 	int dot_dfd_cloexec = open_or_die(".", O_DIRECTORY|O_RDONLY|O_CLOEXEC);
 	int fd = open_or_die("execveat", O_RDONLY);
@@ -353,8 +364,8 @@ static int run_tests(void)
 	/* Attempt to execute relative to non-directory => ENOTDIR */
 	fail += check_execveat_fail(fd, "execveat", 0, ENOTDIR);
 
-	fail += check_execveat_pathmax(dot_dfd, "execveat", 0);
-	fail += check_execveat_pathmax(dot_dfd, "script", 1);
+	fail += check_execveat_pathmax(root_dfd, "execveat", 0);
+	fail += check_execveat_pathmax(root_dfd, "script", 1);
 	return fail;
 }
 
-- 
2.11.0