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ovl: fix regression caused by exclusive upper/work dir protection
Enforcing exclusive ownership on upper/work dirs caused a docker
regression: https://github.com/moby/moby/issues/34672.
Euan spotted the regression and pointed to the offending commit.
Vivek has brought the regression to my attention and provided this
reproducer:
Terminal 1:
mount -t overlay -o workdir=work,lowerdir=lower,upperdir=upper none
merged/
Terminal 2:
unshare -m
Terminal 1:
umount merged
mount -t overlay -o workdir=work,lowerdir=lower,upperdir=upper none
merged/
mount: /root/overlay-testing/merged: none already mounted or mount point
busy
To fix the regression, I replaced the error with an alarming warning.
With index feature enabled, mount does fail, but logs a suggestion to
override exclusive dir protection by disabling index.
Note that index=off mount does take the inuse locks, so a concurrent
index=off will issue the warning and a concurrent index=on mount will fail.
Documentation was updated to reflect this change.
Fixes: 2cac0c00a6
("ovl: get exclusive ownership on upper/work dirs")
Cc: <stable@vger.kernel.org> # v4.13
Reported-by: Euan Kemp <euank@euank.com>
Reported-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
parent
5820dc0888
commit
85fdee1eef
3 changed files with 26 additions and 9 deletions
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@ -210,8 +210,11 @@ path as another overlay mount and it may use a lower layer path that is
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beneath or above the path of another overlay lower layer path.
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Using an upper layer path and/or a workdir path that are already used by
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another overlay mount is not allowed and will fail with EBUSY. Using
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another overlay mount is not allowed and may fail with EBUSY. Using
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partially overlapping paths is not allowed but will not fail with EBUSY.
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If files are accessed from two overlayfs mounts which share or overlap the
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upper layer and/or workdir path the behavior of the overlay is undefined,
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though it will not result in a crash or deadlock.
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Mounting an overlay using an upper layer path, where the upper layer path
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was previously used by another mounted overlay in combination with a
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@ -37,6 +37,9 @@ struct ovl_fs {
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bool noxattr;
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/* sb common to all layers */
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struct super_block *same_sb;
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/* Did we take the inuse lock? */
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bool upperdir_locked;
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bool workdir_locked;
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};
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/* private information held for every overlayfs dentry */
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@ -211,9 +211,10 @@ static void ovl_put_super(struct super_block *sb)
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dput(ufs->indexdir);
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dput(ufs->workdir);
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ovl_inuse_unlock(ufs->workbasedir);
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if (ufs->workdir_locked)
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ovl_inuse_unlock(ufs->workbasedir);
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dput(ufs->workbasedir);
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if (ufs->upper_mnt)
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if (ufs->upper_mnt && ufs->upperdir_locked)
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ovl_inuse_unlock(ufs->upper_mnt->mnt_root);
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mntput(ufs->upper_mnt);
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for (i = 0; i < ufs->numlower; i++)
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@ -881,9 +882,13 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
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goto out_put_upperpath;
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err = -EBUSY;
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if (!ovl_inuse_trylock(upperpath.dentry)) {
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pr_err("overlayfs: upperdir is in-use by another mount\n");
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if (ovl_inuse_trylock(upperpath.dentry)) {
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ufs->upperdir_locked = true;
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} else if (ufs->config.index) {
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pr_err("overlayfs: upperdir is in-use by another mount, mount with '-o index=off' to override exclusive upperdir protection.\n");
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goto out_put_upperpath;
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} else {
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pr_warn("overlayfs: upperdir is in-use by another mount, accessing files from both mounts will result in undefined behavior.\n");
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}
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err = ovl_mount_dir(ufs->config.workdir, &workpath);
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@ -901,9 +906,13 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
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}
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err = -EBUSY;
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if (!ovl_inuse_trylock(workpath.dentry)) {
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pr_err("overlayfs: workdir is in-use by another mount\n");
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if (ovl_inuse_trylock(workpath.dentry)) {
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ufs->workdir_locked = true;
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} else if (ufs->config.index) {
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pr_err("overlayfs: workdir is in-use by another mount, mount with '-o index=off' to override exclusive workdir protection.\n");
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goto out_put_workpath;
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} else {
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pr_warn("overlayfs: workdir is in-use by another mount, accessing files from both mounts will result in undefined behavior.\n");
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}
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ufs->workbasedir = workpath.dentry;
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@ -1156,11 +1165,13 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
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out_free_lowertmp:
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kfree(lowertmp);
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out_unlock_workdentry:
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ovl_inuse_unlock(workpath.dentry);
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if (ufs->workdir_locked)
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ovl_inuse_unlock(workpath.dentry);
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out_put_workpath:
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path_put(&workpath);
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out_unlock_upperdentry:
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ovl_inuse_unlock(upperpath.dentry);
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if (ufs->upperdir_locked)
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ovl_inuse_unlock(upperpath.dentry);
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out_put_upperpath:
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path_put(&upperpath);
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out_free_config:
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