Re: revert "fs/befs/linuxvfs.c: replace strncpy by strlcpy"

From: Fabian Frederick
Date: Tue Apr 28 2015 - 01:35:25 EST

> On 28 April 2015 at 05:48 Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
> commit 39d7a29f867bd5a4a551fad6bb3812ceddb0bce1
> Author: Fabian Frederick <fabf@xxxxxxxxx>
> Date:Â ÂFri Jun 6 14:36:15 2014 -0700
>Â Â Âfs/befs/linuxvfs.c: replace strncpy by strlcpy
>Â Â Â
>Â Â Âstrncpy + end of string assignment replaced by strlcpy
> replaces perfectly safe code with undefined behaviour. All in the name
> of "security hardening", presumably. Folks, seeing the words "designed to be
> safer, more consistent, and less error prone replacement" in a manpage does
> *NOT* mean "OK, quit reading it - no need to go further, not even to the end
> of the paragraph". Because in the end of that paragraph it says "This means
> that for strlcpy() src must be NUL-terminated". And sure enough, our
> implementation relies on that - it starts with strlen().
> strncpy() is guaranteed not to look further than size. strlcpy() is *NOT*.
> strncpy() on unvalidated source is safe, provided that you sanitize the copy;
> strlcpy() on anything like that is an invitation for nasal daemons.
> Sure, we can (and probably should) make strlcpy(dst, src, n) never access
> memory beyond src + n - 1, but this kind of cargo-culting is a Bad Thing(tm);
> mindless "security improvements" without so much as bothering to RTFM are
> asking for trouble. And in userland code anything like that _can't_ be
> papered over afterwards - not unless you can patch every libc implementation
> out there.
> This particular code is completely pointless - if anything, it should've been
> memcpy() + nd_terminate_link()...
> Al, very unhappy about the prospect of looking through ~2000 calls of
> strlcpy()
> we have in the tree...

Sorry Al, I thought it was more secure.
I guess the 2 following patches should be reversed as well :

"fs/befs/btree.c: replace strncpy by strlcpy + coding style fixing"

"fs/ocfs2/super.c: use OCFS2_MAX_VOL_LABEL_LEN and strlcpy"

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