[PATCH 5.15 139/917] ovl: fix filattr copy-up failure

Greg Kroah-Hartman
2021-11-15T23:32:21Z

From: Miklos Szeredi <mszeredi@redhat.com>

commit 5b0a414d06c3ed2097e32ef7944a4abb644b89bd upstream.

This regression can be reproduced with ntfs-3g and overlayfs:

mkdir lower upper work overlay
dd if=/dev/zero of=ntfs.raw bs=1M count=2
mkntfs -F ntfs.raw
mount ntfs.raw lower
touch lower/file.txt
mount -t overlay -o lowerdir=lower,upperdir=upper,workdir=work - overlay
mv overlay/file.txt overlay/file2.txt

mv fails and (misleadingly) prints

mv: cannot move 'overlay/file.txt' to a subdirectory of itself, 'overlay/file2.txt'

The reason is that ovl_copy_fileattr() is triggered due to S_NOATIME being
set on all inodes (by fuse) regardless of fileattr.

ovl_copy_fileattr() tries to retrieve file attributes from lower file, but
that fails because filesystem does not support this ioctl (this should fail
with ENOTTY, but ntfs-3g return EINVAL instead). This failure is
propagated to origial operation (in this case rename) that triggered the
copy-up.

The fix is to ignore ENOTTY and EINVAL errors from fileattr_get() in copy
up. This also requires turning the internal ENOIOCTLCMD into ENOTTY.

As a further measure to prevent unnecessary failures, only try the
fileattr_get/set on upper if there are any flags to copy up.

Side note: a number of filesystems set S_NOATIME (and sometimes other inode
flags) irrespective of fileattr flags. This causes unnecessary calls
during copy up, which might lead to a performance issue, especially if
latency is high. To fix this, the kernel would need to differentiate
between the two cases. E.g. introduce SB_NOATIME_UPDATE, a per-sb variant
of S_NOATIME. SB_NOATIME doesn't work, because that's interpreted as
"filesystem doesn't store an atime attribute"

Reported-and-tested-by: Kevin Locke <kevin@kevinlocke.name>
Fixes: 72db82115d2b ("ovl: copy up sync/noatime fileattr flags")
Cc: <stable@vger.kernel.org> # v5.15
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/overlayfs/copy_up.c | 23 ++++++++++++++++++-----
fs/overlayfs/inode.c | 5 ++++-
2 files changed, 22 insertions(+), 6 deletions(-)

--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -140,12 +140,14 @@ static int ovl_copy_fileattr(struct inod
int err;

err = ovl_real_fileattr_get(old, &oldfa);
- if (err)
- return err;
-
- err = ovl_real_fileattr_get(new, &newfa);
- if (err)
+ if (err) {
+ /* Ntfs-3g returns -EINVAL for "no fileattr support" */
+ if (err == -ENOTTY || err == -EINVAL)
+ return 0;
+ pr_warn("failed to retrieve lower fileattr (%pd2, err=%i)\n",
+ old, err);
return err;
+ }

/*
* We cannot set immutable and append-only flags on upper inode,
@@ -159,6 +161,17 @@ static int ovl_copy_fileattr(struct inod
return err;
}

+ /* Don't bother copying flags if none are set */
+ if (!(oldfa.flags & OVL_COPY_FS_FLAGS_MASK))
+ return 0;
+
+ err = ovl_real_fileattr_get(new, &newfa);
+ if (err) {
+ pr_warn("failed to retrieve upper fileattr (%pd2, err=%i)\n",
+ new, err);
+ return err;
+ }
+
BUILD_BUG_ON(OVL_COPY_FS_FLAGS_MASK & ~FS_COMMON_FL);
newfa.flags &= ~OVL_COPY_FS_FLAGS_MASK;
newfa.flags |= (oldfa.flags & OVL_COPY_FS_FLAGS_MASK);
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -610,7 +610,10 @@ int ovl_real_fileattr_get(struct path *r
if (err)
return err;

- return vfs_fileattr_get(realpath->dentry, fa);
+ err = vfs_fileattr_get(realpath->dentry, fa);
+ if (err == -ENOIOCTLCMD)
+ err = -ENOTTY;
+ return err;
}

int ovl_fileattr_get(struct dentry *dentry, struct fileattr *fa)