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53 lines
2.1 KiB
Diff
53 lines
2.1 KiB
Diff
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From a6138db815df5ee542d848318e5dae681590fccd Mon Sep 17 00:00:00 2001
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From: "Eric W. Biederman" <ebiederm@xmission.com>
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Date: Mon, 28 Jul 2014 16:26:53 -0700
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Subject: [PATCH] mnt: Only change user settable mount flags in remount
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Kenton Varda <kenton@sandstorm.io> discovered that by remounting a
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read-only bind mount read-only in a user namespace the
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MNT_LOCK_READONLY bit would be cleared, allowing an unprivileged user
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to the remount a read-only mount read-write.
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Correct this by replacing the mask of mount flags to preserve
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with a mask of mount flags that may be changed, and preserve
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all others. This ensures that any future bugs with this mask and
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remount will fail in an easy to detect way where new mount flags
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simply won't change.
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Cc: stable@vger.kernel.org
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Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>
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Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
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---
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fs/namespace.c | 2 +-
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include/linux/mount.h | 4 +++-
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2 files changed, 4 insertions(+), 2 deletions(-)
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diff --git a/fs/namespace.c b/fs/namespace.c
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index 7187d01329c35..cb40449ea0dfe 100644
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--- a/fs/namespace.c
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+++ b/fs/namespace.c
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@@ -1937,7 +1937,7 @@ static int do_remount(struct path *path, int flags, int mnt_flags,
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err = do_remount_sb(sb, flags, data, 0);
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if (!err) {
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lock_mount_hash();
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- mnt_flags |= mnt->mnt.mnt_flags & MNT_PROPAGATION_MASK;
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+ mnt_flags |= mnt->mnt.mnt_flags & ~MNT_USER_SETTABLE_MASK;
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mnt->mnt.mnt_flags = mnt_flags;
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touch_mnt_namespace(mnt->mnt_ns);
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unlock_mount_hash();
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diff --git a/include/linux/mount.h b/include/linux/mount.h
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index 839bac2709048..b637a89e1faeb 100644
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--- a/include/linux/mount.h
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+++ b/include/linux/mount.h
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@@ -42,7 +42,9 @@ struct mnt_namespace;
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* flag, consider how it interacts with shared mounts.
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*/
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#define MNT_SHARED_MASK (MNT_UNBINDABLE)
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-#define MNT_PROPAGATION_MASK (MNT_SHARED | MNT_UNBINDABLE)
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+#define MNT_USER_SETTABLE_MASK (MNT_NOSUID | MNT_NODEV | MNT_NOEXEC \
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+ | MNT_NOATIME | MNT_NODIRATIME | MNT_RELATIME \
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+ | MNT_READONLY)
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#define MNT_INTERNAL_FLAGS (MNT_SHARED | MNT_WRITE_HOLD | MNT_INTERNAL | \
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MNT_DOOMED | MNT_SYNC_UMOUNT | MNT_MARKED)
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