From ffbc6f0ead47fa5a1dc9642b0331cb75c20a640e Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Mon, 28 Jul 2014 17:36:04 -0700 Subject: [PATCH] mnt: Change the default remount atime from relatime to the existing value Since March 2009 the kernel has treated the state that if no MS_..ATIME flags are passed then the kernel defaults to relatime. Defaulting to relatime instead of the existing atime state during a remount is silly, and causes problems in practice for people who don't specify any MS_...ATIME flags and to get the default filesystem atime setting. Those users may encounter a permission error because the default atime setting does not work. A default that does not work and causes permission problems is ridiculous, so preserve the existing value to have a default atime setting that is always guaranteed to work. Using the default atime setting in this way is particularly interesting for applications built to run in restricted userspace environments without /proc mounted, as the existing atime mount options of a filesystem can not be read from /proc/mounts. In practice this fixes user space that uses the default atime setting on remount that are broken by the permission checks keeping less privileged users from changing more privileged users atime settings. Cc: stable@vger.kernel.org Acked-by: Serge E. Hallyn Signed-off-by: "Eric W. Biederman" --- fs/namespace.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/fs/namespace.c b/fs/namespace.c index dd9c93b5a9d5..7886176232c1 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -2473,6 +2473,14 @@ long do_mount(const char *dev_name, const char *dir_name, if (flags & MS_RDONLY) mnt_flags |= MNT_READONLY; + /* The default atime for remount is preservation */ + if ((flags & MS_REMOUNT) && + ((flags & (MS_NOATIME | MS_NODIRATIME | MS_RELATIME | + MS_STRICTATIME)) == 0)) { + mnt_flags &= ~MNT_ATIME_MASK; + mnt_flags |= path.mnt->mnt_flags & MNT_ATIME_MASK; + } + flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE | MS_BORN | MS_NOATIME | MS_NODIRATIME | MS_RELATIME| MS_KERNMOUNT | MS_STRICTATIME); -- 2.20.1