[Bug preprocessor/66318] New: Error messages contain raw file name; malicious #line directives can do bad things

["Keith.S.Thompson at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66318

            Bug ID: 66318
           Summary: Error messages contain raw file name; malicious #line
                    directives can do bad things
           Product: gcc
           Version: 5.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: preprocessor
          Assignee: unassigned at gcc dot gnu.org
          Reporter: Keith.S.Thompson at gmail dot com
  Target Milestone: ---

Error messages include the (presumed) name of the source file in which
the error was detected. The #line directive can set the presumed file name
to nearly any arbitrary string, possibly including control characters.

A directive like:

#line __LINE__ "beep\a.c"

can cause every printed error message to beep.  More malicious #line
directives can cause even more obnoxious behavior.

The sample file shown below, when fed through the preprocessor (either
directly or via the "gcc" command), will change the screen foreground
to green and the background to red if the command is run under xterm.

Depending on which terminal emulator is being used and how it's
configured, it might even be possible to trigger arbitrary code execution
just by compiling a source file.

System: Linux Mint 17.
gcc version 5.1.0, built from source with:
gcc-5.1.0/configure --prefix=/usr/local/apps/gcc-5.1.0 --disable-multilib

Test case (a 2 line source file named "red_green.c"):
#line __LINE__ "'\x1b]10;green\a\x1b]11;red\a'"
#error "Argh! My eyes!"

Output of "cpp red_green.c 2>&1 | cat -A":
'^[]10;green^G^[]11;red^G':1:2: error: #error "Argh! My eyes!"$
# 1 "red_green.c"$
# 1 "<built-in>"$
# 1 "<command-line>"$
# 1 "/usr/include/stdc-predef.h" 1 3 4$
# 1 "<command-line>" 2$
# 1 "red_green.c"$
# 1 "'^[]10;green^G^[]11;red^G'"$

See the "xtermcontrol" command for other possibilities. Even if
arbitrary command execution isn't possible, maximizing the current
window and rapidly alternating between red and green would be at least
seriously annoying, and at worst potentially dangerous to epileptics
(the latter is speculation on my part).

Suggested fix: Sanitize the displayed file name for error messages so
only printable characters are displayed (presumably affected by the
current locale).