ovl: fix corner case of conflicting lower layer uuid

This fixes ovl_lower_uuid_ok() to correctly detect the corner case:
 - two filesystems, A and B, both have null uuid
 - upper layer is on A
 - lower layer 1 is also on A
 - lower layer 2 is on B

In this case, bad_uuid would not have been set for B, because the check
only involved the list of lower fs.  Hence we'll try to decode a layer 2
origin on layer 1 and fail.

We check for conflicting (and null) uuid among all lower layers, including
those layers that are on the same fs as the upper layer.

Reported-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
index d9fbebd..c9324ad 100644 (file)
--- a/fs/overlayfs/ovl_entry.h
+++ b/fs/overlayfs/ovl_entry.h
@@ -24,6 +24,8 @@ struct ovl_sb {
        dev_t pseudo_dev;
        /* Unusable (conflicting) uuid */
        bool bad_uuid;
+       /* Used as a lower layer (but maybe also as upper) */
+       bool is_lower;
 };
 
 struct ovl_layer {

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index d7c406d..7cf5436 100644 (file)
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -1260,7 +1260,7 @@ static bool ovl_lower_uuid_ok(struct ovl_fs *ofs, const uuid_t *uuid)
        if (!ofs->config.nfs_export && !ofs->upper_mnt)
                return true;
 
-       for (i = 1; i < ofs->numfs; i++) {
+       for (i = 0; i < ofs->numfs; i++) {
                /*
                 * We use uuid to associate an overlay lower file handle with a
                 * lower layer, so we can accept lower fs with null uuid as long
@@ -1268,7 +1268,8 @@ static bool ovl_lower_uuid_ok(struct ovl_fs *ofs, const uuid_t *uuid)
                 * if we detect multiple lower fs with the same uuid, we
                 * disable lower file handle decoding on all of them.
                 */
-               if (uuid_equal(&ofs->fs[i].sb->s_uuid, uuid)) {
+               if (ofs->fs[i].is_lower &&
+                   uuid_equal(&ofs->fs[i].sb->s_uuid, uuid)) {
                        ofs->fs[i].bad_uuid = true;
                        return false;
                }
@@ -1342,10 +1343,12 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
        /*
         * All lower layers that share the same fs as upper layer, use the real
         * upper st_dev.
+        * is_lower will be set if upper fs is shared with a lower layer.
         */
        if (ofs->upper_mnt) {
                ofs->fs[0].sb = ofs->upper_mnt->mnt_sb;
                ofs->fs[0].pseudo_dev = ofs->upper_mnt->mnt_sb->s_dev;
+               ofs->fs[0].is_lower = false;
        }
 
        for (i = 0; i < numlower; i++) {
@@ -1387,6 +1390,7 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
                ofs->layers[ofs->numlayer].fsid = fsid;
                ofs->layers[ofs->numlayer].fs = &ofs->fs[fsid];
                ofs->numlayer++;
+               ofs->fs[fsid].is_lower = true;
        }
 
        /*