From 64cb2da8dca18e00893bcf7aa2955d93fd9acac9 Mon Sep 17 00:00:00 2001 From: Tycho Andersen Date: Thu, 9 Jan 2020 16:52:41 -0700 Subject: [PATCH] libmount: do not unnecessarily chmod utab.lock MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Before ecfeae90a294 ("libmount: Ensure utab.lock mode 644"), you could do something like: irc:/tmp umount --version umount from util-linux 2.27.1 (libmount 2.27.0: selinux, assert, debug) irc:/tmp mkdir foo bar irc:/tmp unshare -Urm irc:/tmp mount --bind foo bar irc:/tmp umount bar irc:/tmp echo $? 0 However, afterwards, you get: /tmp unshare -Urm /tmp mount --bind foo bar /tmp umount bar umount: /tmp/bar: filesystem was unmounted, but failed to update userspace mount table. Because of the chmod failing: fchmod(3, 0644)                         = -1 EPERM (Operation not permitted) Let's figure out whether the chmod is necessary before doing it, and only do it if it is necessary. This won't fix cases where the system is already broken, but at least on healthy systems umount will behave as before. Signed-off-by: Tycho Andersen --- libmount/src/lock.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/libmount/src/lock.c b/libmount/src/lock.c index 484841fbcf..cc5340db18 100644 --- a/libmount/src/lock.c +++ b/libmount/src/lock.c @@ -204,6 +204,8 @@ static int lock_simplelock(struct libmnt_lock *ml) { const char *lfile; int rc; + struct stat sb; + const mode_t lock_mask = S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH; assert(ml); assert(ml->simplelock); @@ -225,12 +227,21 @@ static int lock_simplelock(struct libmnt_lock *ml) rc = -errno; goto err; } - rc = fchmod(ml->lockfile_fd, S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH); + + rc = fstat(ml->lockfile_fd, &sb); if (rc < 0) { rc = -errno; goto err; } + if ((sb.st_mode & lock_mask) != lock_mask) { + rc = fchmod(ml->lockfile_fd, lock_mask); + if (rc < 0) { + rc = -errno; + goto err; + } + } + while (flock(ml->lockfile_fd, LOCK_EX) < 0) { int errsv; if ((errno == EAGAIN) || (errno == EINTR)) -- 2.47.3