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authorAmir Goldstein <amir73il@gmail.com>2017-09-29 10:21:21 +0300
committerMiklos Szeredi <mszeredi@redhat.com>2017-10-05 15:53:18 +0200
commit85fdee1eef1a9e48ad5716916677e0c5fbc781e3 (patch)
tree9f2096f14047af5ce55aacfc9a7b90a7f7405f09
parent5820dc0888d302ac05f8b91ffdf7e4e53b4fbf53 (diff)
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: 2cac0c00a6cd ("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>
-rw-r--r--Documentation/filesystems/overlayfs.txt5
-rw-r--r--fs/overlayfs/ovl_entry.h3
-rw-r--r--fs/overlayfs/super.c27
3 files changed, 26 insertions, 9 deletions
diff --git a/Documentation/filesystems/overlayfs.txt b/Documentation/filesystems/overlayfs.txt
index 36f528a7fdd6..8caa60734647 100644
--- a/Documentation/filesystems/overlayfs.txt
+++ b/Documentation/filesystems/overlayfs.txt
@@ -210,8 +210,11 @@ path as another overlay mount and it may use a lower layer path that is
beneath or above the path of another overlay lower layer path.
Using an upper layer path and/or a workdir path that are already used by
-another overlay mount is not allowed and will fail with EBUSY. Using
+another overlay mount is not allowed and may fail with EBUSY. Using
partially overlapping paths is not allowed but will not fail with EBUSY.
+If files are accessed from two overlayfs mounts which share or overlap the
+upper layer and/or workdir path the behavior of the overlay is undefined,
+though it will not result in a crash or deadlock.
Mounting an overlay using an upper layer path, where the upper layer path
was previously used by another mounted overlay in combination with a
diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
index 878a750986dd..25d9b5adcd42 100644
--- a/fs/overlayfs/ovl_entry.h
+++ b/fs/overlayfs/ovl_entry.h
@@ -37,6 +37,9 @@ struct ovl_fs {
bool noxattr;
/* sb common to all layers */
struct super_block *same_sb;
+ /* Did we take the inuse lock? */
+ bool upperdir_locked;
+ bool workdir_locked;
};
/* private information held for every overlayfs dentry */
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index fd5ea4facc62..092d150643c1 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -211,9 +211,10 @@ static void ovl_put_super(struct super_block *sb)
dput(ufs->indexdir);
dput(ufs->workdir);
- ovl_inuse_unlock(ufs->workbasedir);
+ if (ufs->workdir_locked)
+ ovl_inuse_unlock(ufs->workbasedir);
dput(ufs->workbasedir);
- if (ufs->upper_mnt)
+ if (ufs->upper_mnt && ufs->upperdir_locked)
ovl_inuse_unlock(ufs->upper_mnt->mnt_root);
mntput(ufs->upper_mnt);
for (i = 0; i < ufs->numlower; i++)
@@ -881,9 +882,13 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
goto out_put_upperpath;
err = -EBUSY;
- if (!ovl_inuse_trylock(upperpath.dentry)) {
- pr_err("overlayfs: upperdir is in-use by another mount\n");
+ if (ovl_inuse_trylock(upperpath.dentry)) {
+ ufs->upperdir_locked = true;
+ } else if (ufs->config.index) {
+ pr_err("overlayfs: upperdir is in-use by another mount, mount with '-o index=off' to override exclusive upperdir protection.\n");
goto out_put_upperpath;
+ } else {
+ pr_warn("overlayfs: upperdir is in-use by another mount, accessing files from both mounts will result in undefined behavior.\n");
}
err = ovl_mount_dir(ufs->config.workdir, &workpath);
@@ -901,9 +906,13 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
}
err = -EBUSY;
- if (!ovl_inuse_trylock(workpath.dentry)) {
- pr_err("overlayfs: workdir is in-use by another mount\n");
+ if (ovl_inuse_trylock(workpath.dentry)) {
+ ufs->workdir_locked = true;
+ } else if (ufs->config.index) {
+ pr_err("overlayfs: workdir is in-use by another mount, mount with '-o index=off' to override exclusive workdir protection.\n");
goto out_put_workpath;
+ } else {
+ pr_warn("overlayfs: workdir is in-use by another mount, accessing files from both mounts will result in undefined behavior.\n");
}
ufs->workbasedir = workpath.dentry;
@@ -1156,11 +1165,13 @@ out_put_lowerpath:
out_free_lowertmp:
kfree(lowertmp);
out_unlock_workdentry:
- ovl_inuse_unlock(workpath.dentry);
+ if (ufs->workdir_locked)
+ ovl_inuse_unlock(workpath.dentry);
out_put_workpath:
path_put(&workpath);
out_unlock_upperdentry:
- ovl_inuse_unlock(upperpath.dentry);
+ if (ufs->upperdir_locked)
+ ovl_inuse_unlock(upperpath.dentry);
out_put_upperpath:
path_put(&upperpath);
out_free_config: