selftests/exec: include cwd in long path calculation

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 <[email protected]>

---
 tools/testing/selftests/exec/execveat.c | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

tools/testing/selftests/exec/execveat.c +1 -1

index 8d5d1d2ee7c1..5edc609c778b 100644
@@ -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;

tools/testing/selftests/exec/execveat.c +8 -1

+
+               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;

tools/testing/selftests/exec/execveat.c +5 -5

@@ -200,10 +209,10 @@ 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 +227,7 @@ 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 +363,8 @@ 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;
 }
 
--

2.15.0.rc0.271.g36b669edcc-goog

Modulo the minor comment below:

Reviewed-by David Drysdale <[email protected]>

Quoted 30 lines · Steve Muckle

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 <[email protected]>

---
  tools/testing/selftests/exec/execveat.c | 24 +++++++++++++++++-------
  1 file changed, 17 insertions(+), 7 deletions(-)

tools/testing/selftests/exec/execveat.c +1 -1

index 8d5d1d2ee7c1..5edc609c778b 100644
@@ -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;

@@ -156,15 +156,24 @@ static int check_execveat_pathmax(int dot_dfd, const char *src, int is_script)
 

tools/testing/selftests/exec/execveat.c static int check_execveat_pathmax(int dot_dfd, const char *src, int is_script) · line 159

Quoted 3 lines

tools/testing/selftests/exec/execveat.c +1 -0

         if (*longpath == '\0') {
                 /* Create a filename close to PATH_MAX in length */
+               char *cwd = getcwd(NULL, 0);

cwd never gets freed, but that's presumably not a problem unless these tests ever get run under some kind of leak checker.

Quoted 13 lines

tools/testing/selftests/exec/execveat.c +8 -1

+
+               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;

tools/testing/selftests/exec/execveat.c static int check_execveat_pathmax(int dot_dfd, const char *src, int is_script) · line 179

Quoted 10 lines

tools/testing/selftests/exec/execveat.c +2 -1

+               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);

There's a missing comment update around here-ish:
* Execute as a long pathname relative to ".".
(should now be 'relative to "/"' I think).