[PATCH 1/2] run-command: Add checks after execvp fails with EACCES

@@ -2,6 +2,7 @@
 #include "run-command.h"
 #include "exec_cmd.h"
 #include "argv-array.h"
+#include "dir.h"
 
 static inline void close_pair(int fd[2])
 {

@@ -134,6 +135,119 @@ static int wait_or_whine(pid_t pid, const char *argv0, int silent_exec_failure)
 	return code;
 }
 
+#ifndef WIN32
+static int is_in_group(gid_t gid)
+{
+	gid_t *groups;
+	int ngroups, gc;
+	int yes;
+
+	if (gid == getgid())
+		return 1;
+
+	groups = NULL;
+	ngroups = getgroups(0, NULL);
+	if (ngroups > 0) {
+		groups = (gid_t *)xmalloc(ngroups * sizeof(gid_t));
+		if (getgroups(ngroups, groups) < 0) {
+			free(groups);
+			return 0;
+		}
+	}
+
+	yes = 0;
+	for (gc = 0; gc < ngroups; gc++)
+		if (groups[gc] == gid)
+			yes = 1;
+
+	free(groups);
+	return yes;
+}
+
+static int have_read_execute_permissions(const char *path)
+{
+	struct stat s;
+	trace_printf("checking '%s'\n", path);
+
+	if (stat(path, &s) < 0) {
+		trace_printf("could not stat '%s': %s\n",
+				path, strerror(errno));
+		return 0;
+	}
+	trace_printf("uid: %d, gid: %d\n", s.st_uid, s.st_gid);
+	trace_printf("mode: %o\n", s.st_mode);
+
+	/* check world permissions */
+	if ((s.st_mode&(S_IXOTH|S_IROTH)) == (S_IXOTH|S_IROTH))
+		return 1;
+
+	/* check group permissions & membership */
+	if ((s.st_mode&(S_IXGRP|S_IRGRP)) == (S_IXGRP|S_IRGRP) &&
+		is_in_group(s.st_gid))
+		return 1;
+
+	/* check owner permissions & ownership */
+	if ((s.st_mode&(S_IXUSR|S_IRUSR)) == (S_IXUSR|S_IRUSR) &&
+		s.st_uid == getuid())
+		return 1;
+
+	return 0;
+}
+
+static void diagnose_execvp_eacces(const char *cmd, const char **argv)
+{
+	/* man 2 execve states that EACCES is returned for:
+	 * - Search permission is denied on a component of the path prefix
+	 *   of cmd or the name of a script interpreter
+	 * - The file or script interpreter is not a regular file
+	 * - Execute permission is denied for the file, script or ELF
+	 *   interpreter
+	 * - The file system is mounted noexec
+	 */
+	struct strbuf sb = STRBUF_INIT;
+	char *path = getenv("PATH");
+	char *next;
+
+	if (strchr(cmd, '/')) {
+		if (!have_read_execute_permissions(cmd))
+			error("no read/execute permissions on '%s'\n", cmd);
+		return;
+	}
+
+	for (;;) {
+		next = strchrnul(path, ':');
+		if (path < next)
+			strbuf_add(&sb, path, next - path);
+		else
+			strbuf_addch(&sb, '.');
+
+		if (!have_read_execute_permissions(sb.buf))
+			error("no read/execute permissions on '%s'\n", sb.buf);
+
+		if (sb.len && sb.buf[sb.len - 1] != '/')
+			strbuf_addch(&sb, '/');
+		strbuf_addstr(&sb, cmd);
+
+		if (file_exists(sb.buf)) {
+			if (!have_read_execute_permissions(sb.buf))
+				error("no read/execute permissions on '%s'\n",
+						sb.buf);
+			else
+				warn("file '%s' exists and permissions "
+				"seem OK.\nIf this is a script, see if you "
+				"have sufficient privileges to run the "
+				"interpreter", sb.buf);
+		}
+
+		strbuf_release(&sb);
+
+		if (!*next)
+			break;
+		path = next + 1;
+	}
+}
+#endif
+
 int start_command(struct child_process *cmd)
 {
 	int need_in, need_out, need_err;

@@ -285,6 +399,10 @@ fail_pipe:
 				error("cannot run %s: %s", cmd->argv[0],
 					strerror(ENOENT));
 			exit(127);
+		} else if (errno == EACCES) {
+			diagnose_execvp_eacces(cmd->argv[0], cmd->argv);
+			die("cannot exec '%s': %s", cmd->argv[0],
+				strerror(EACCES));
 		} else {
 			die_errno("cannot exec '%s'", cmd->argv[0]);
 		}

@@ -26,7 +26,7 @@ test_expect_success 'run_command can run a command' '
 	test_cmp empty err
 '
 
-test_expect_success POSIXPERM 'run_command reports EACCES' '
+test_expect_success POSIXPERM 'run_command reports EACCES, file permissions' '
 	cat hello-script >hello.sh &&
 	chmod -x hello.sh &&
 	test_must_fail test-run-command run-command ./hello.sh 2>err &&

@@ -34,4 +34,18 @@ test_expect_success POSIXPERM 'run_command reports EACCES' '
 	grep "fatal: cannot exec.*hello.sh" err
 '
 
+test_expect_success POSIXPERM 'run_command reports EACCES, search path permisions' '
+	mkdir -p inaccessible &&
+	PATH=$(pwd)/inaccessible:$PATH &&
+	export PATH &&
+
+	cat hello-script >inaccessible/hello.sh &&
+	chmod 400 inaccessible &&
+	test_must_fail test-run-command run-command hello.sh 2>err &&
+	chmod 755 inaccessible &&
+
+	grep "fatal: cannot exec.*hello.sh" err &&
+	grep "no read/execute permissions on" err
+'
+
 test_done