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. > > Link: https://github.com/util-linux/util-linux/issues/2298 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@xxxxxxxxxxxxxxx I'll fix this up for you though.
