[RFC] problems with alloc_file_pseudo() use in __nfs42_ssc_open()

Al Viro
2022-08-17T21:55:23Z

My apologies for having missed that back when the SSC
patchset had been done (and missing the problems after it got
merged, actually).

1) if this
r_ino = nfs_fhget(ss_mnt->mnt_sb, src_fh, fattr);
in __nfs42_ssc_open() yields a directory inode, we are screwed
as soon as it's passed to alloc_file_pseudo() - a *lot* of places
in dcache handling would break if we do that. It's not too
nice for a regular file from non-cooperating filesystem, but for
directory ones it's deadly.

2) if alloc_file_pseudo() fails there, we get an inode leak. It
needs an iput() for that case. As in
if (IS_ERR(filep)) {
res = ERR_CAST(filep);
iput(r_ino);
goto out_free_name;
}

But I'd like to point out that alloc_file_pseudo() is not inteded for
use on normal filesystem's inodes - the use here *mostly* works
(directories aside), but... Use it on filesystem with non-trivial
default dentry_operations and things will get interesting, etc.