ovl: refactor ovl_fill_super()

Split the core into a separate helper in preparation of converting the
caller to the scoped ovl cred guard.

Link: https://patch.msgid.link/20251117-work-ovl-cred-guard-v4-40-b31603935724@kernel.org
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 7b8fc1cab6eb856088739f8a416e413619c47972..a3e54db441bd316adb7a8ab88477ecb909b70581 100644 (file)
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -1364,53 +1364,35 @@ static void ovl_set_d_op(struct super_block *sb)
        set_default_d_op(sb, &ovl_dentry_operations);
 }
 
-int ovl_fill_super(struct super_block *sb, struct fs_context *fc)
+static int ovl_fill_super_creds(struct fs_context *fc, struct super_block *sb)
 {
        struct ovl_fs *ofs = sb->s_fs_info;
+       struct cred *creator_cred = (struct cred *)ofs->creator_cred;
        struct ovl_fs_context *ctx = fc->fs_private;
-       const struct cred *old_cred = NULL;
-       struct dentry *root_dentry;
-       struct ovl_entry *oe;
        struct ovl_layer *layers;
-       struct cred *cred;
+       struct ovl_entry *oe = NULL;
        int err;
 
-       err = -EIO;
-       if (WARN_ON(fc->user_ns != current_user_ns()))
-               goto out_err;
-
-       ovl_set_d_op(sb);
-
-       err = -ENOMEM;
-       if (!ofs->creator_cred)
-               ofs->creator_cred = cred = prepare_creds();
-       else
-               cred = (struct cred *)ofs->creator_cred;
-       if (!cred)
-               goto out_err;
-
-       old_cred = ovl_override_creds(sb);
-
        err = ovl_fs_params_verify(ctx, &ofs->config);
        if (err)
-               goto out_err;
+               return err;
 
        err = -EINVAL;
        if (ctx->nr == 0) {
                if (!(fc->sb_flags & SB_SILENT))
                        pr_err("missing 'lowerdir'\n");
-               goto out_err;
+               return err;
        }
 
        err = -ENOMEM;
        layers = kcalloc(ctx->nr + 1, sizeof(struct ovl_layer), GFP_KERNEL);
        if (!layers)
-               goto out_err;
+               return err;
 
        ofs->config.lowerdirs = kcalloc(ctx->nr + 1, sizeof(char *), GFP_KERNEL);
        if (!ofs->config.lowerdirs) {
                kfree(layers);
-               goto out_err;
+               return err;
        }
        ofs->layers = layers;
        /*
@@ -1443,12 +1425,12 @@ int ovl_fill_super(struct super_block *sb, struct fs_context *fc)
                err = -EINVAL;
                if (!ofs->config.workdir) {
                        pr_err("missing 'workdir'\n");
-                       goto out_err;
+                       return err;
                }
 
                err = ovl_get_upper(sb, ofs, &layers[0], &ctx->upper);
                if (err)
-                       goto out_err;
+                       return err;
 
                upper_sb = ovl_upper_mnt(ofs)->mnt_sb;
                if (!ovl_should_sync(ofs)) {
@@ -1456,13 +1438,13 @@ int ovl_fill_super(struct super_block *sb, struct fs_context *fc)
                        if (errseq_check(&upper_sb->s_wb_err, ofs->errseq)) {
                                err = -EIO;
                                pr_err("Cannot mount volatile when upperdir has an unseen error. Sync upperdir fs to clear state.\n");
-                               goto out_err;
+                               return err;
                        }
                }
 
                err = ovl_get_workdir(sb, ofs, &ctx->upper, &ctx->work);
                if (err)
-                       goto out_err;
+                       return err;
 
                if (!ofs->workdir)
                        sb->s_flags |= SB_RDONLY;
@@ -1473,7 +1455,7 @@ int ovl_fill_super(struct super_block *sb, struct fs_context *fc)
        oe = ovl_get_lowerstack(sb, ctx, ofs, layers);
        err = PTR_ERR(oe);
        if (IS_ERR(oe))
-               goto out_err;
+               return err;
 
        /* If the upper fs is nonexistent, we mark overlayfs r/o too */
        if (!ovl_upper_mnt(ofs))
@@ -1526,7 +1508,7 @@ int ovl_fill_super(struct super_block *sb, struct fs_context *fc)
                sb->s_export_op = &ovl_export_fid_operations;
 
        /* Never override disk quota limits or use reserved space */
-       cap_lower(cred->cap_effective, CAP_SYS_RESOURCE);
+       cap_lower(creator_cred->cap_effective, CAP_SYS_RESOURCE);
 
        sb->s_magic = OVERLAYFS_SUPER_MAGIC;
        sb->s_xattr = ovl_xattr_handlers(ofs);
@@ -1544,27 +1526,50 @@ int ovl_fill_super(struct super_block *sb, struct fs_context *fc)
        sb->s_iflags |= SB_I_EVM_HMAC_UNSUPPORTED;
 
        err = -ENOMEM;
-       root_dentry = ovl_get_root(sb, ctx->upper.dentry, oe);
-       if (!root_dentry)
+       sb->s_root = ovl_get_root(sb, ctx->upper.dentry, oe);
+       if (!sb->s_root)
                goto out_free_oe;
 
-       sb->s_root = root_dentry;
-
-       ovl_revert_creds(old_cred);
        return 0;
 
 out_free_oe:
        ovl_free_entry(oe);
+       return err;
+}
+
+int ovl_fill_super(struct super_block *sb, struct fs_context *fc)
+{
+       struct ovl_fs *ofs = sb->s_fs_info;
+       const struct cred *old_cred = NULL;
+       struct cred *cred;
+       int err;
+
+       err = -EIO;
+       if (WARN_ON(fc->user_ns != current_user_ns()))
+               goto out_err;
+
+       ovl_set_d_op(sb);
+
+       err = -ENOMEM;
+       if (!ofs->creator_cred)
+               ofs->creator_cred = cred = prepare_creds();
+       else
+               cred = (struct cred *)ofs->creator_cred;
+       if (!cred)
+               goto out_err;
+
+       old_cred = ovl_override_creds(sb);
+
+       err = ovl_fill_super_creds(fc, sb);
+
+       ovl_revert_creds(old_cred);
+
 out_err:
-       /*
-        * Revert creds before calling ovl_free_fs() which will call
-        * put_cred() and put_cred() requires that the cred's that are
-        * put are not the caller's creds, i.e., current->cred.
-        */
-       if (old_cred)
-               ovl_revert_creds(old_cred);
-       ovl_free_fs(ofs);
-       sb->s_fs_info = NULL;
+       if (err) {
+               ovl_free_fs(ofs);
+               sb->s_fs_info = NULL;
+       }
+
        return err;
 }