On Wed, Jun 07, 2023 at 07:28:48PM +0200, Thomas Weißschuh wrote:
As each option string fragment is always prepended with a comma it would happen that the whole string always starts with a comma. This could be interpreted by filesystem drivers as an empty option and may produce errors.
For example the NTFS driver from ntfs.ko behaves like this and fails when mounted via the new API.
Yeah, the old ntfs driver implements its own option parser. It overwrites/splits at ',' returning '\0' and then trips over this.
Contrast with e.g., ovl_next_op() which does the same thing but skips over '\0' in ovl_parse_opt().
So arguably also a bug in ntfs parsing. But there's no reason we should prepend ',' for legacy mount option strings.
And yeah, I can easily verify this...
Using my custom move-mount tool I originally wrote for another patchset but which is handy to pass mount options via the new mount api _system_ calls and not via mount(): https://github.com/brauner/move-mount-beneath
I can do:
sudo ./move-mount -f overlay -olowerdir=/mnt/a:/mnt/b,upperdir=/mnt/upper,workdir=/mnt/work /mnt/merged
and clearly see:
> sudo bpftrace -e 'kfunc:legacy_get_tree { @m = args->fc; printf("%s\n", str(((struct legacy_fs_context *)@m->fs_private)->legacy_data)); }' Attaching 1 probe... ,lowerdir=/mnt/a:/mnt/b,upperdir=/mnt/upper,workdir=/mnt/work
Fixes: 3e1aeb00e6d1 ("vfs: Implement a filesystem superblock creation/configuration context")
Should be:
Fixes: commit 3e1aeb00e6d1 ("vfs: Implement a filesystem superblock creation/configuration context")
and misses a:
Cc: stable@vger.kernel.org
I'll fix this up for you though.