ovl: get exclusive ownership on upper/work dirs
Bad things can happen if several concurrent overlay mounts try to
use the same upperdir/workdir path.
Try to get the 'inuse' advisory lock on upperdir and workdir.
Fail mount if another overlay mount instance or another user
holds the 'inuse' lock on these directories.
Note that this provides no protection for concurrent overlay
mount that use overlapping (i.e. descendant) upper/work dirs.
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index e0a51ea..b316377 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -204,6 +204,10 @@
unsigned i;
dput(ufs->workdir);
+ ovl_inuse_unlock(ufs->workbasedir);
+ dput(ufs->workbasedir);
+ if (ufs->upper_mnt)
+ ovl_inuse_unlock(ufs->upper_mnt->mnt_root);
mntput(ufs->upper_mnt);
for (i = 0; i < ufs->numlower; i++)
mntput(ufs->lower_mnt[i]);
@@ -821,9 +825,15 @@
if (err)
goto out_put_upperpath;
+ err = -EBUSY;
+ if (!ovl_inuse_trylock(upperpath.dentry)) {
+ pr_err("overlayfs: upperdir is in-use by another mount\n");
+ goto out_put_upperpath;
+ }
+
err = ovl_mount_dir(ufs->config.workdir, &workpath);
if (err)
- goto out_put_upperpath;
+ goto out_unlock_upperdentry;
err = -EINVAL;
if (upperpath.mnt != workpath.mnt) {
@@ -834,12 +844,20 @@
pr_err("overlayfs: workdir and upperdir must be separate subtrees\n");
goto out_put_workpath;
}
+
+ err = -EBUSY;
+ if (!ovl_inuse_trylock(workpath.dentry)) {
+ pr_err("overlayfs: workdir is in-use by another mount\n");
+ goto out_put_workpath;
+ }
+
+ ufs->workbasedir = workpath.dentry;
sb->s_stack_depth = upperpath.mnt->mnt_sb->s_stack_depth;
}
err = -ENOMEM;
lowertmp = kstrdup(ufs->config.lowerdir, GFP_KERNEL);
if (!lowertmp)
- goto out_put_workpath;
+ goto out_unlock_workdentry;
err = -EINVAL;
stacklen = ovl_split_lowerdirs(lowertmp);
@@ -882,6 +900,7 @@
pr_err("overlayfs: failed to clone upperpath\n");
goto out_put_lowerpath;
}
+
/* Don't inherit atime flags */
ufs->upper_mnt->mnt_flags &= ~(MNT_NOATIME | MNT_NODIRATIME | MNT_RELATIME);
@@ -1004,7 +1023,7 @@
mntput(upperpath.mnt);
for (i = 0; i < numlower; i++)
mntput(stack[i].mnt);
- path_put(&workpath);
+ mntput(workpath.mnt);
kfree(lowertmp);
if (upperpath.dentry) {
@@ -1043,8 +1062,12 @@
kfree(stack);
out_free_lowertmp:
kfree(lowertmp);
+out_unlock_workdentry:
+ ovl_inuse_unlock(workpath.dentry);
out_put_workpath:
path_put(&workpath);
+out_unlock_upperdentry:
+ ovl_inuse_unlock(upperpath.dentry);
out_put_upperpath:
path_put(&upperpath);
out_free_config: