From: Christian Brauner <christian.brauner@ubuntu.com> To: Alexander Viro <viro@zeniv.linux.org.uk>, Christoph Hellwig <hch@infradead.org>, linux-fsdevel@vger.kernel.org Cc: Andy Lutomirski <luto@kernel.org>, Mimi Zohar <zohar@linux.ibm.com>, James Bottomley <James.Bottomley@hansenpartnership.com>, Andreas Dilger <adilger.kernel@dilger.ca>, containers@lists.linux-foundation.org, Christoph Hellwig <hch@lst.de>, Tycho Andersen <tycho@tycho.ws>, Paul Moore <paul@paul-moore.com>, Jonathan Corbet <corbet@lwn.net>, smbarber@chromium.org, linux-ext4@vger.kernel.org, Mrunal Patel <mpatel@redhat.com>, Kees Cook <keescook@chromium.org>, Arnd Bergmann <arnd@arndb.de>, selinux@vger.kernel.org, Josh Triplett <josh@joshtriplett.org>, Seth Forshee <seth.forshee@canonical.com>, Aleksa Sarai <cyphar@cyphar.com>, Lennart Poettering <lennart@poettering.net>, OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>, Geoffrey Thomas <geofft@ldpreload.com>, David Howells <dhowells@redhat.com>, John Johansen <john.johansen@canonical.com>, Theodore Tso <tytso@mit.edu>, Dmitry Kasatkin <dmitry.kasatkin@gmail.com>, Stephen Smalley <stephen.smalley.work@gmail.com>, linux-security-module@vger.kernel.org, "Eric W. Biederman" <ebiederm@xmission.com>, linux-api@vger.kernel.org, Casey Schaufler <casey@schaufler-ca.com>, Alban Crequy <alban@kinvolk.io>, linux-integrity@vger.kernel.org, Todd Kjos <tkjos@google.com> Subject: [PATCH v4 03/40] namespace: only take read lock in do_reconfigure_mnt() Date: Fri, 4 Dec 2020 00:56:59 +0100 [thread overview] Message-ID: <20201203235736.3528991-4-christian.brauner@ubuntu.com> (raw) In-Reply-To: <20201203235736.3528991-1-christian.brauner@ubuntu.com> do_reconfigure_mnt() used to take the down_write(&sb->s_umount) lock which seems unnecessary since we're not changing the superblock. We're only checking whether it is already read-only. Setting other mount attributes is protected by lock_mount_hash() afaict and not by s_umount. So I think the history of down_write(&sb->s_umount) lock being taken when setting mount attributes dates back to the introduction of MNT_READONLY in [2]. Afaict, this introduced the concept of having read-only mounts in contrast to just having a read-only superblock. When it got introduced it was simply plumbed into do_remount() which already took down_write(&sb->s_umount) because it was only used to actually change the superblock before [2]. Afaict, it would've already been possible back then to only use down_read(&sb->s_umount) for MS_BIND | MS_REMOUNT since actual mount options were protected by the vfsmount lock already. But that would've meant special casing the locking for MS_BIND | MS_REMOUNT in do_remount() which people might not have considered worth it. Then in [1] MS_BIND | MS_REMOUNT mount option changes were split out of do_remount() into do_reconfigure_mnt() but the down_write(&sb->s_umount) lock was simply copied over. Now that we have this be a separate helper only take the down_read(&sb->s_umount) lock since we're only interested in checking whether the super block is currently read-only and blocking any writers from changing it. Essentially, checking that the super block is read-only has the advantage that we can avoid having to go into the slowpath and through MNT_WRITE_HOLD and can simply set the read-only flag on the mount in set_mount_attributes(). [1]: commit 43f5e655eff7 ("vfs: Separate changing mount flags full remount") [2]: commit 2e4b7fcd9260 ("[PATCH] r/o bind mounts: honor mount writer counts at remount") Cc: David Howells <dhowells@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com> Reviewed-by: Christoph Hellwig <hch@lst.de> --- /* v2 */ unchanged /* v3 */ unchanged /* v4 */ unchanged --- fs/namespace.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/fs/namespace.c b/fs/namespace.c index 798bbf4f48ad..8497d149ecaa 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -2512,10 +2512,6 @@ static int change_mount_ro_state(struct mount *mnt, unsigned int mnt_flags) return 0; } -/* - * Update the user-settable attributes on a mount. The caller must hold - * sb->s_umount for writing. - */ static void set_mount_attributes(struct mount *mnt, unsigned int mnt_flags) { mnt_flags |= mnt->mnt.mnt_flags & ~MNT_USER_SETTABLE_MASK; @@ -2565,13 +2561,17 @@ static int do_reconfigure_mnt(struct path *path, unsigned int mnt_flags) if (!can_change_locked_flags(mnt, mnt_flags)) return -EPERM; - down_write(&sb->s_umount); + /* + * We're only checking whether the superblock is read-only not changing + * it, so only take down_read(&sb->s_umount). + */ + down_read(&sb->s_umount); lock_mount_hash(); ret = change_mount_ro_state(mnt, mnt_flags); if (ret == 0) set_mount_attributes(mnt, mnt_flags); unlock_mount_hash(); - up_write(&sb->s_umount); + up_read(&sb->s_umount); mnt_warn_timestamp_expiry(path, &mnt->mnt); -- 2.29.2 _______________________________________________ Containers mailing list Containers@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/containers
WARNING: multiple messages have this Message-ID (diff)
From: Christian Brauner <christian.brauner@ubuntu.com> To: Alexander Viro <viro@zeniv.linux.org.uk>, Christoph Hellwig <hch@infradead.org>, linux-fsdevel@vger.kernel.org Cc: "John Johansen" <john.johansen@canonical.com>, "James Morris" <jmorris@namei.org>, "Mimi Zohar" <zohar@linux.ibm.com>, "Dmitry Kasatkin" <dmitry.kasatkin@gmail.com>, "Stephen Smalley" <stephen.smalley.work@gmail.com>, "Casey Schaufler" <casey@schaufler-ca.com>, "Arnd Bergmann" <arnd@arndb.de>, "Andreas Dilger" <adilger.kernel@dilger.ca>, "OGAWA Hirofumi" <hirofumi@mail.parknet.co.jp>, "Geoffrey Thomas" <geofft@ldpreload.com>, "Mrunal Patel" <mpatel@redhat.com>, "Josh Triplett" <josh@joshtriplett.org>, "Andy Lutomirski" <luto@kernel.org>, "Theodore Tso" <tytso@mit.edu>, "Alban Crequy" <alban@kinvolk.io>, "Tycho Andersen" <tycho@tycho.ws>, "David Howells" <dhowells@redhat.com>, "James Bottomley" <James.Bottomley@hansenpartnership.com>, "Seth Forshee" <seth.forshee@canonical.com>, "Stéphane Graber" <stgraber@ubuntu.com>, "Aleksa Sarai" <cyphar@cyphar.com>, "Lennart Poettering" <lennart@poettering.net>, "Eric W. Biederman" <ebiederm@xmission.com>, smbarber@chromium.org, "Phil Estes" <estesp@gmail.com>, "Serge Hallyn" <serge@hallyn.com>, "Kees Cook" <keescook@chromium.org>, "Todd Kjos" <tkjos@google.com>, "Paul Moore" <paul@paul-moore.com>, "Jonathan Corbet" <corbet@lwn.net>, containers@lists.linux-foundation.org, linux-security-module@vger.kernel.org, linux-api@vger.kernel.org, linux-ext4@vger.kernel.org, linux-integrity@vger.kernel.org, selinux@vger.kernel.org, "Christian Brauner" <christian.brauner@ubuntu.com>, "Christoph Hellwig" <hch@lst.de> Subject: [PATCH v4 03/40] namespace: only take read lock in do_reconfigure_mnt() Date: Fri, 4 Dec 2020 00:56:59 +0100 [thread overview] Message-ID: <20201203235736.3528991-4-christian.brauner@ubuntu.com> (raw) In-Reply-To: <20201203235736.3528991-1-christian.brauner@ubuntu.com> do_reconfigure_mnt() used to take the down_write(&sb->s_umount) lock which seems unnecessary since we're not changing the superblock. We're only checking whether it is already read-only. Setting other mount attributes is protected by lock_mount_hash() afaict and not by s_umount. So I think the history of down_write(&sb->s_umount) lock being taken when setting mount attributes dates back to the introduction of MNT_READONLY in [2]. Afaict, this introduced the concept of having read-only mounts in contrast to just having a read-only superblock. When it got introduced it was simply plumbed into do_remount() which already took down_write(&sb->s_umount) because it was only used to actually change the superblock before [2]. Afaict, it would've already been possible back then to only use down_read(&sb->s_umount) for MS_BIND | MS_REMOUNT since actual mount options were protected by the vfsmount lock already. But that would've meant special casing the locking for MS_BIND | MS_REMOUNT in do_remount() which people might not have considered worth it. Then in [1] MS_BIND | MS_REMOUNT mount option changes were split out of do_remount() into do_reconfigure_mnt() but the down_write(&sb->s_umount) lock was simply copied over. Now that we have this be a separate helper only take the down_read(&sb->s_umount) lock since we're only interested in checking whether the super block is currently read-only and blocking any writers from changing it. Essentially, checking that the super block is read-only has the advantage that we can avoid having to go into the slowpath and through MNT_WRITE_HOLD and can simply set the read-only flag on the mount in set_mount_attributes(). [1]: commit 43f5e655eff7 ("vfs: Separate changing mount flags full remount") [2]: commit 2e4b7fcd9260 ("[PATCH] r/o bind mounts: honor mount writer counts at remount") Cc: David Howells <dhowells@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com> Reviewed-by: Christoph Hellwig <hch@lst.de> --- /* v2 */ unchanged /* v3 */ unchanged /* v4 */ unchanged --- fs/namespace.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/fs/namespace.c b/fs/namespace.c index 798bbf4f48ad..8497d149ecaa 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -2512,10 +2512,6 @@ static int change_mount_ro_state(struct mount *mnt, unsigned int mnt_flags) return 0; } -/* - * Update the user-settable attributes on a mount. The caller must hold - * sb->s_umount for writing. - */ static void set_mount_attributes(struct mount *mnt, unsigned int mnt_flags) { mnt_flags |= mnt->mnt.mnt_flags & ~MNT_USER_SETTABLE_MASK; @@ -2565,13 +2561,17 @@ static int do_reconfigure_mnt(struct path *path, unsigned int mnt_flags) if (!can_change_locked_flags(mnt, mnt_flags)) return -EPERM; - down_write(&sb->s_umount); + /* + * We're only checking whether the superblock is read-only not changing + * it, so only take down_read(&sb->s_umount). + */ + down_read(&sb->s_umount); lock_mount_hash(); ret = change_mount_ro_state(mnt, mnt_flags); if (ret == 0) set_mount_attributes(mnt, mnt_flags); unlock_mount_hash(); - up_write(&sb->s_umount); + up_read(&sb->s_umount); mnt_warn_timestamp_expiry(path, &mnt->mnt); -- 2.29.2
next prev parent reply other threads:[~2020-12-04 0:02 UTC|newest] Thread overview: 98+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-12-03 23:56 [PATCH v4 00/40] idmapped mounts Christian Brauner 2020-12-03 23:56 ` Christian Brauner 2020-12-03 23:56 ` [PATCH v4 01/40] namespace: take lock_mount_hash() directly when changing flags Christian Brauner 2020-12-03 23:56 ` Christian Brauner 2020-12-03 23:56 ` [PATCH v4 02/40] mount: make {lock,unlock}_mount_hash() static Christian Brauner 2020-12-03 23:56 ` Christian Brauner 2020-12-03 23:56 ` Christian Brauner [this message] 2020-12-03 23:56 ` [PATCH v4 03/40] namespace: only take read lock in do_reconfigure_mnt() Christian Brauner 2020-12-03 23:57 ` [PATCH v4 04/40] fs: split out functions to hold writers Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-07 17:08 ` Christoph Hellwig 2020-12-07 17:08 ` Christoph Hellwig 2020-12-03 23:57 ` [PATCH v4 05/40] fs: add attr_flags_to_mnt_flags helper Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-07 17:10 ` Christoph Hellwig 2020-12-07 17:10 ` Christoph Hellwig 2020-12-08 10:07 ` Christian Brauner 2020-12-08 10:07 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 06/40] fs: add mount_setattr() Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-07 17:14 ` Christoph Hellwig 2020-12-07 17:14 ` Christoph Hellwig 2020-12-08 10:37 ` Christian Brauner 2020-12-08 10:37 ` Christian Brauner 2020-12-08 15:05 ` Christoph Hellwig 2020-12-08 15:05 ` Christoph Hellwig 2020-12-08 15:22 ` Christian Brauner 2020-12-08 15:22 ` Christian Brauner 2020-12-08 15:26 ` Christian Brauner 2020-12-08 15:26 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 07/40] tests: add mount_setattr() selftests Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 08/40] fs: add id translation helpers Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 09/40] mount: attach mappings to mounts Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 10/40] capability: handle idmapped mounts Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 11/40] namei: make permission helpers idmapped mount aware Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 12/40] inode: make init and " Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 13/40] attr: handle idmapped mounts Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 14/40] acl: " Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 15/40] xattr: " Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 16/40] commoncap: " Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 17/40] stat: " Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 18/40] namei: handle idmapped mounts in may_*() helpers Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 19/40] namei: introduce struct renamedata Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 20/40] namei: prepare for idmapped mounts Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 21/40] open: handle idmapped mounts in do_truncate() Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 22/40] open: handle idmapped mounts Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 23/40] af_unix: " Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 24/40] utimes: " Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 25/40] fcntl: " Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 26/40] notify: " Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 27/40] init: " Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 28/40] ioctl: " Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 29/40] would_dump: " Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 30/40] exec: " Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 31/40] fs: make helpers idmap mount aware Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 32/40] apparmor: handle idmapped mounts Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 33/40] ima: " Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 34/40] fat: " Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 35/40] ext4: support " Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 36/40] ecryptfs: do not mount on top of " Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 37/40] overlayfs: " Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 38/40] fs: introduce MOUNT_ATTR_IDMAP Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 39/40] tests: extend mount_setattr tests Christian Brauner 2020-12-03 23:57 ` Christian Brauner 2020-12-03 23:57 ` [PATCH v4 40/40] generic/618: add fstests for idmapped mounts Christian Brauner 2020-12-03 23:57 ` Christian Brauner
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