Re: tar extraction fails on a CIFS file system, due to a symlink

[Paul Eggert]

On 12/21/24 07:18, Bruno Haible via Bug reports for GNU Tar wrote:
> Possible suggestion: Report it as a bug to the Linux kernel people?

That sounds best. If the CIFS kernel module can't support setting 
symlink timestamps on , it should fail with ENOTSUP rather than follow 
the symlink.

Symlinks seem to be a sore spot with Samba and there's been some recent 
symlink activity in linux/fs/smb/client (e.g., [1]) and I imagine on the 
server side as well, so the problem may be specific to a specific Linux 
kernel or CIFS server version or their combination.


> Alternate suggestion: Delay utimensat() calls until the end of the 'tar' run?
>    (Then 'tar' would have set wrong time stamps but exited with code 0.)

I don't see how that would help. If utimensat ignores 
AT_SYMLINK_NOFOLLOW, an attacker can craft a tarball that can set 
timestamps on any file the victim has access to. This would be true even 
if tar delayed utimensat calls.

Presumably other apps are also affected by this bug, and I imagine they 
can't easily work around it either.


[1]: 
https://github.com/torvalds/linux/commit/6a832bc8bbb22350f7ffe6ecb2d36f261bb96023