linux-kernel - [PATCH AUTOSEL 5.19 34/48] ovl: warn if trusted xattr creation fails

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Message-Id: <20220814161943.2394452-34-sashal@kernel.org>
Date:   Sun, 14 Aug 2022 12:19:27 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Miklos Szeredi <mszeredi@...hat.com>,
        Alois Wohlschlager <alois1@...-topmail.de>,
        Sasha Levin <sashal@...nel.org>, miklos@...redi.hu,
        linux-unionfs@...r.kernel.org
Subject: [PATCH AUTOSEL 5.19 34/48] ovl: warn if trusted xattr creation fails

From: Miklos Szeredi <mszeredi@...hat.com>

[ Upstream commit b10b85fe5149ee8b39fbbf86095b303632dde2cd ]

When mounting overlayfs in an unprivileged user namespace, trusted xattr
creation will fail.  This will lead to failures in some file operations,
e.g. in the following situation:

  mkdir lower upper work merged
  mkdir lower/directory
  mount -toverlay -olowerdir=lower,upperdir=upper,workdir=work none merged
  rmdir merged/directory
  mkdir merged/directory

The last mkdir will fail:

  mkdir: cannot create directory 'merged/directory': Input/output error

The cause for these failures is currently extremely non-obvious and hard to
debug.  Hence, warn the user and suggest using the userxattr mount option,
if it is not already supplied and xattr creation fails during the
self-check.

Reported-by: Alois Wohlschlager <alois1@...-topmail.de>
Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/overlayfs/super.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 1ce5c9698393..4c2096130209 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -1418,11 +1418,12 @@ static int ovl_make_workdir(struct super_block *sb, struct ovl_fs *ofs,
 	 */
 	err = ovl_setxattr(ofs, ofs->workdir, OVL_XATTR_OPAQUE, "0", 1);
 	if (err) {
+		pr_warn("failed to set xattr on upper\n");
 		ofs->noxattr = true;
 		if (ofs->config.index || ofs->config.metacopy) {
 			ofs->config.index = false;
 			ofs->config.metacopy = false;
-			pr_warn("upper fs does not support xattr, falling back to index=off,metacopy=off.\n");
+			pr_warn("...falling back to index=off,metacopy=off.\n");
 		}
 		/*
 		 * xattr support is required for persistent st_ino.
@@ -1430,8 +1431,10 @@ static int ovl_make_workdir(struct super_block *sb, struct ovl_fs *ofs,
 		 */
 		if (ofs->config.xino == OVL_XINO_AUTO) {
 			ofs->config.xino = OVL_XINO_OFF;
-			pr_warn("upper fs does not support xattr, falling back to xino=off.\n");
+			pr_warn("...falling back to xino=off.\n");
 		}
+		if (err == -EPERM && !ofs->config.userxattr)
+			pr_info("try mounting with 'userxattr' option\n");
 		err = 0;
 	} else {
 		ovl_removexattr(ofs, ofs->workdir, OVL_XATTR_OPAQUE);
-- 
2.35.1