[PATCH] ovl: warn if trusted xattr creation fails

[Alois Wohlschlager <alois1@gmx-topmail.de>]

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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.

Signed-off-by: Alois Wohlschlager <alois1@gmx-topmail.de>
---
 fs/overlayfs/super.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 7bb0a47cb615..11123fe967e0 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -1427,6 +1427,8 @@ static int ovl_make_workdir(struct super_block *sb,
struct ovl_fs *ofs,
 			ofs->config.xino = OVL_XINO_OFF;
 			pr_warn("upper fs does not support xattr,
falling back to xino=off.\n");
 		}
+		if (!ofs->config.userxattr)
+			pr_warn("trusted xattr creation not
supported, some file operations may fail. Try mounting with userxattr next
time.\n");
 		err = 0;
 	} else {
 		ovl_do_removexattr(ofs, ofs->workdir, OVL_XATTR_OPAQUE);
--
2.35.1


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