simon-git: putty (main): Simon Tatham

[Commits to Tartarus hosted VCS]

TL;DR:
  dff4bd4d Improve error reporting from x11_verify().
  8e7e3c59 Improve time-safety of XDM-AUTHORIZATION-1 validation.

Repository:     https://git.tartarus.org/simon/putty.git
On the web:     https://git.tartarus.org/?p=simon/putty.git
Branch updated: main
Committer:      Simon Tatham <anakin at pobox.com>
Date:           2023-04-01 16:12:57

commit dff4bd4d14c4c2abbfa689f9a8f0cd876db5dcc7
web diff https://git.tartarus.org/?p=simon/putty.git;a=commitdiff;h=dff4bd4d14c4c2abbfa689f9a8f0cd876db5dcc7;hp=cedeb75d59ce0c4b5b18270dbada6976ba07d7b1
Author: Simon Tatham <anakin at pobox.com>
Date:   Sat Apr 1 15:53:29 2023 +0100

    Improve error reporting from x11_verify().
    
    Now the return value is a dynamically allocated string instead of a
    static one, which means that the error message can include details
    taken from the specific failing connection. In particular, if someone
    requests an X11 authorisation protocol we don't support, we can print
    its name as part of the message, which may help users debug the
    problem.
    
    One particularly important special case of this is that if the client
    connection presents _no_ authorisation - which is surely by far the
    most likely thing to happen by accident, e.g. if the auth file has
    gone missing, or the hostname doesn't match for some reason - then we
    now give a specific message "No authorisation provided", which I think
    is considerably more helpful than just lumping that very common case
    in with "Unsupported authorisation protocol". Even changing the latter
    to "Unsupported authorisation protocol ''" is still not very sensible.
    The problem in that case is not that the user has tried an exotic auth
    protocol we've never heard of - it's that they've forgotten, or
    failed, to provide one at all.
    
    The error message for "XDM-AUTHORIZATION-1 data was wrong length" is
    the other modified one: it now says what the wrong length _was_.
    However, all other failures of X-A-1 are still kept deliberately
    vague, because saying which part of the decrypted string didn't match
    is an obvious information leak.

 ssh/x11fwd.c | 65 +++++++++++++++++++++++++++++++++++++++---------------------
 1 file changed, 42 insertions(+), 23 deletions(-)

commit 8e7e3c59448013be44b8cba2b7f89a894ee34113
web diff https://git.tartarus.org/?p=simon/putty.git;a=commitdiff;h=8e7e3c59448013be44b8cba2b7f89a894ee34113;hp=dff4bd4d14c4c2abbfa689f9a8f0cd876db5dcc7
Author: Simon Tatham <anakin at pobox.com>
Date:   Sat Apr 1 16:07:29 2023 +0100

    Improve time-safety of XDM-AUTHORIZATION-1 validation.
    
    While writing the previous patch, I realise that walking along a
    decrypted string and stopping to complain about the first mismatch you
    find is an anti-pattern. If we're going to deliberately give the same
    error message for various mismatches, so as not to give away which
    part failed first, then we should also avoid giving away the same
    information via a timing leak!
    
    I don't think this is serious enough to warrant the full-on advisory
    protocol, because XDM-AUTHORIZATION-1 is rarely used these days and
    also DES-based, so there are bigger problems with it. (Plus, why on
    earth is it based on encryption anyway, not a MAC?) But since I
    spotted it in passing, might as well fix it.

 ssh/x11fwd.c | 30 ++++++++++++++++--------------
 1 file changed, 16 insertions(+), 14 deletions(-)