libXfont -- BDF parsing issues

Alan Coopersmith reports:

Ilja van Sprundel, a security researcher with IOActive, has
discovered an issue in the parsing of BDF font files by libXfont.
Additional testing by Alan Coopersmith and William Robinet with
the American Fuzzy Lop (afl) tool uncovered two more issues in
the parsing of BDF font files.
As libXfont is used by the X server to read font files, and an
unprivileged user with access to the X server can tell the X
server to read a given font file from a path of their choosing,
these vulnerabilities have the potential to allow unprivileged
users to run code with the privileges of the X server
(often root access).