bug#15648: 24.2.50; gnutls SSL connection to IMAP server causes emacs to crash completely, bug#15648: 24.2.50; gnutls SSL connection to IMAP server causes emacs to crash completely

[Eli Zaretskii <eliz@gnu.org>]

> From: <emacs@kosowsky.org>
> Date: Wed, 23 Oct 2013 00:17:49 -0400
> Cc: Ted Zlatanov <tzz@lifelogs.com>, 15648@debbugs.gnu.org
> 
> Stepping through the *Lisp* code shows that the file paths are all
> properly parsed when cygwin-mount is loaded/activated. Indeed,
> file-exists-p properly recognizes the cygwin path
> "/usr/ssl/certs/ca-bundle.crt" and returns nil on the other paths that
> don't exist in a standard Cygwin setup.
> 
> Note that if cygwin-mount is not loaded/activated, then
> "/usr/ssl/certs/ca-bundle.crt" (along with the other list elements)
> fails the file-exists-p test in gnutls-negotiate so that 'trustfiles'
> gets set to nil which explains why it doesn't crash in the case when
> cygwin-mount is not used since trivially 'trustfiles' has no paths
> associated with it.
> 
> So, basically, we have the following Catch-22. If cygwin-mount is not
> loaded/activated, then the cert location for Cygwin is never found. If
> cygwin-mount is activated then it causes a crash. The result being
> that in Windows, no certs are ever loaded when using the default
> definition of gnutls-trustfiles
> 
> Presumably the problem is that the C-code doesn't know how to deal with
> a Cygwin (*nix) style path that has been properly recognized by the
> Lisp code (via cygwin-mount).

The native Windows build of Emacs certainly doesn't understand the
magic of Cygwin mounts.  How can it?  The cygwin-mount package cannot
possibly work for external DLLs that were developed for native Windows
builds of programs which know nothing about Lisp and Emacs file I/O.

The problem is almost certainly that the GnuTLS code was assured that
a file exists (because Emacs used cygwin-mount), but then the file
could not be reached.  I can understand why GnuTLS becomes confused.

But since you didn't provide any C-level backtraces, we cannot know
where that code is, and thus cannot fix it.

> It seems like there are two potential solutions:
> 1. Use Windows-style paths in the definition of gnutls-trustfiles
>    (this should work in Linux too, since
>    "C:/usr/ssl/certs/ca-bundle.crt" will generally fail the
>    file-exists-p test)
> 
> 2. Add cygwin-mount functionality to the C-code so that it can parse
>    cygwin (Unix) style paths.

 3. Do not use cygwin-mount in conjunction with the native Windows
    build of Emacs.

> In any case, I imagine the C-code crashes because it sees a Unix-style
> path while expecting a Windows style path...

Windows supports Unix-style file names.  The problem is that the file
"/usr/ssl/certs/ca-bundle.crt" cannot be found by starting from the
root directory of the current drive.

> that being said the C-code should be better behaved than that... at
> a minimum the code should check to make sure the certificate file
> path is well-formed and exists.

See above: unless you present the backtrace from the crash, no one can
know where the offending code is, or what it does wrong.  Please
provide that data.