tree 47002b74b82fd5ab5423a32214a875cac1db5710
parent 2c8d700e8af297a813db1eaae5d45b7b07ac72b6
author Willy Tarreau <w@1wt.eu> 1409596555 +0200
committer Willy Tarreau <w@1wt.eu> 1409658615 +0200
encoding latin1

BUG/CRITICAL: http: don't update msg->sov once data start to leave the buffer

Commit bb2e669 ("BUG/MAJOR: http: correctly rewind the request body
after start of forwarding") was incorrect/incomplete. It used to rely on
CF_READ_ATTACHED to stop updating msg->sov once data start to leave the
buffer, but this is unreliable because since commit a6eebb3 ("[BUG]
session: clear BF_READ_ATTACHED before next I/O") merged in 1.5-dev1,
this flag is only ephemeral and is cleared once all analysers have
seen it. So we can start updating msg->sov again each time we pass
through this place with new data. With a sufficiently large amount of
data, it is possible to make msg->sov wrap and validate the if()
condition at the top, causing the buffer to advance by about 2GB and
crash the process.

Note that the offset cannot be controlled by the attacker because it is
a sum of millions of small random sizes depending on how many bytes were
read by the server and how many were left in the buffer, only because
of the speed difference between reading and writing. Also, nothing is
written, the invalid pointer resulting from this operation is only read.

Many thanks to James Dempsey for reporting this bug and to Chris Forbes for
narrowing down the faulty area enough to make its root cause analysable.

This fix must be backported to haproxy 1.5.
(cherry picked from commit a2d002aeb669a9bbca2dcd3e6be71615f435e9e6)