51 lines
1.7 KiB
Diff
51 lines
1.7 KiB
Diff
From: "Eric W. Biederman" <ebiederm@xmission.com>
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Date: Mon, 28 Jul 2014 17:10:56 -0700
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Subject: [2/5] mnt: Move the test for MNT_LOCK_READONLY from
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change_mount_flags into do_remount
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Origin: https://git.kernel.org/linus/07b645589dcda8b7a5249e096fece2a67556f0f4
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There are no races as locked mount flags are guaranteed to never change.
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Moving the test into do_remount makes it more visible, and ensures all
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filesystem remounts pass the MNT_LOCK_READONLY permission check. This
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second case is not an issue today as filesystem remounts are guarded
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by capable(CAP_DAC_ADMIN) and thus will always fail in less privileged
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mount namespaces, but it could become an issue in the future.
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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 | 13 ++++++++++---
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1 file changed, 10 insertions(+), 3 deletions(-)
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--- a/fs/namespace.c
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+++ b/fs/namespace.c
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@@ -1898,9 +1898,6 @@ static int change_mount_flags(struct vfs
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if (readonly_request == __mnt_is_readonly(mnt))
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return 0;
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- if (mnt->mnt_flags & MNT_LOCK_READONLY)
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- return -EPERM;
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-
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if (readonly_request)
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error = mnt_make_readonly(real_mount(mnt));
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else
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@@ -1926,6 +1923,16 @@ static int do_remount(struct path *path,
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if (path->dentry != path->mnt->mnt_root)
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return -EINVAL;
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+ /* Don't allow changing of locked mnt flags.
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+ *
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+ * No locks need to be held here while testing the various
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+ * MNT_LOCK flags because those flags can never be cleared
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+ * once they are set.
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+ */
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+ if ((mnt->mnt.mnt_flags & MNT_LOCK_READONLY) &&
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+ !(mnt_flags & MNT_READONLY)) {
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+ return -EPERM;
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+ }
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err = security_sb_remount(sb, data);
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if (err)
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return err;
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