[tor-bugs] #13538 [Tor]: Stop signed left shift overflows in curve25519-donna (non-64-bit)

[Tor Bug Tracker & Wiki]

#13538: Stop signed left shift overflows in curve25519-donna (non-64-bit)
---------------------------------------+----------------------------------
 Reporter:  teor                       |          Owner:
     Type:  defect                     |         Status:  new
 Priority:  normal                     |      Milestone:
Component:  Tor                        |        Version:  Tor: unspecified
 Keywords:  tor-router integer-safety  |  Actual Points:
Parent ID:                             |         Points:
---------------------------------------+----------------------------------
 Similarly to #13280, the curve25519-donna.c code contains some signed left
 shifts of negative numbers, which clang identifies as runtime errors.
 (This is only an issue with the generic code, not the 64-bit code.)

 Under -ftrapv, this causes a trap/crash.

 I've used a similar strategy to the one in #13280, where we automate the
 entire SHL32/SHL64 conversion using a perl script. The first commit sets
 up the macros.

 The safe SHL32/SHL64 macros perform potentially overflowing left shifts in
 unsigned arithmetic.

 I'll post a branch as soon as I've set up a change entry (for which I need
 the bug number).

 Version: tor 2.6.?-alpha
 git: fc5cab44724e8328e2186f22114625388f1c8f0d (Thu Oct 16 13:29:14 2014
 -0400)

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/13538>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online