[Bug 271174] NFS readdir truncates dirent fileid to 32 bits

From: <bugzilla-noreply_at_freebsd.org>
Date: Mon, 01 May 2023 16:19:33 UTC

            Bug ID: 271174
           Summary: NFS readdir truncates dirent fileid to 32 bits
           Product: Base System
           Version: 12.4-RELEASE
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: kern
          Assignee: bugs@FreeBSD.org
          Reporter: bmueller@panasas.com

The return result of an NFS readdir rpc include directory entries (dirents). 
According to NFSv3 RFC, the struct entry3 (which represent the dirents)
contains type fileid3 for the fileid.  fileid3 is a 64 bit number.

However, we can see that in the FreeBSD kernel NFS server, when assembling the
dirent, the server only marshalls 32 bits of the d_fileno:
 This results in the lower 32 bits of the fileno being transmitted.

This manifests as a problem with the libc getcwd call because under some
circumstances, getcwd wants to manually determine the cwd by doing a series of
readdirs, comparing the inode number (fileid) from the direntries with a stat
of the current directory.  Stat (NFS getattr) will return a 64 bit fileid, but
the readdir will be 32 bits, so the comparison never matches and getcwd fails.

The NFS server can be fixed by doing 64 bit fileid marshalling for NFSv3/4,
while leaving it as 32 bits for NFSv2 where fileid.

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