ovl: Ensure that all layers have the same encoding

When merging layers from different filesystems with casefold enabled,
all layers should use the same encoding version and have the same flags
to avoid any kind of incompatibility issues.

Also, set the encoding and the encoding flags for the ovl super block as
the same as used by the first valid layer.

Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: André Almeida <andrealmeid@igalia.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index df85a76597e910d00323018f1d2cd720c5db921d..548ea9b1a48d4b709d1096d8baf0506cbd8b0eee 100644 (file)
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -991,6 +991,25 @@ static int ovl_get_data_fsid(struct ovl_fs *ofs)
        return ofs->numfs;
 }
 
+/*
+ * Set the ovl sb encoding as the same one used by the first layer
+ */
+static int ovl_set_encoding(struct super_block *sb, struct super_block *fs_sb)
+{
+       if (!sb_has_encoding(fs_sb))
+               return 0;
+
+#if IS_ENABLED(CONFIG_UNICODE)
+       if (sb_has_strict_encoding(fs_sb)) {
+               pr_err("strict encoding not supported\n");
+               return -EINVAL;
+       }
+
+       sb->s_encoding = fs_sb->s_encoding;
+       sb->s_encoding_flags = fs_sb->s_encoding_flags;
+#endif
+       return 0;
+}
 
 static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
                          struct ovl_fs_context *ctx, struct ovl_layer *layers)
@@ -1024,6 +1043,12 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
        if (ovl_upper_mnt(ofs)) {
                ofs->fs[0].sb = ovl_upper_mnt(ofs)->mnt_sb;
                ofs->fs[0].is_lower = false;
+
+               if (ofs->casefold) {
+                       err = ovl_set_encoding(sb, ofs->fs[0].sb);
+                       if (err)
+                               return err;
+               }
        }
 
        nr_merged_lower = ctx->nr - ctx->nr_data;
@@ -1083,6 +1108,19 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
                l->name = NULL;
                ofs->numlayer++;
                ofs->fs[fsid].is_lower = true;
+
+               if (ofs->casefold) {
+                       if (!ovl_upper_mnt(ofs) && !sb_has_encoding(sb)) {
+                               err = ovl_set_encoding(sb, ofs->fs[fsid].sb);
+                               if (err)
+                                       return err;
+                       }
+
+                       if (!sb_same_encoding(sb, mnt->mnt_sb)) {
+                               pr_err("all layers must have the same encoding\n");
+                               return -EINVAL;
+                       }
+               }
        }
 
        /*