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Don't use env::current_exe with libbacktrace #33554

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Don't use env::current_exe with libbacktrace
If the path we give to libbacktrace doesn't actually correspond to the
current process, libbacktrace will segfault *at best*.

cc #21889
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sfackler committed May 12, 2016
commit 9393e52d4d2705698a6dfdd2834d41154ee23b64
49 changes: 12 additions & 37 deletions src/libstd/sys/common/gnu/libbacktrace.rs
Original file line number Diff line number Diff line change
@@ -15,7 +15,6 @@ use sys_common::backtrace::{output, output_fileline};

pub fn print(w: &mut Write, idx: isize, addr: *mut libc::c_void,
symaddr: *mut libc::c_void) -> io::Result<()> {
use env;
use ffi::CStr;
use ptr;

@@ -110,46 +109,22 @@ pub fn print(w: &mut Write, idx: isize, addr: *mut libc::c_void,
// that is calculated the first time this is requested. Remember that
// backtracing all happens serially (one global lock).
//
// An additionally oddity in this function is that we initialize the
// filename via self_exe_name() to pass to libbacktrace. It turns out
// that on Linux libbacktrace seamlessly gets the filename of the
// current executable, but this fails on freebsd. by always providing
// it, we make sure that libbacktrace never has a reason to not look up
// the symbols. The libbacktrace API also states that the filename must
// be in "permanent memory", so we copy it to a static and then use the
// static as the pointer.
// Things don't work so well on not-Linux since libbacktrace can't track
// down that executable this is. We at one point used env::current_exe but
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is this meant to say: "down what executable this is. ..." ?

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Oops, yeah.

// it turns out that there are some serious security issues with that
// approach.
//
// FIXME: We also call self_exe_name() on DragonFly BSD. I haven't
// tested if this is required or not.
// Specifically, on certain platforms like BSDs, a malicious actor can cause
// an arbitrary file to be placed at the path returned by current_exe.
// libbacktrace does not behave defensively in the presence of ill-formed
// DWARF information, and has been demonstrated to segfault in at least one
// case. There is no evidence at the moment to suggest that a more carefully
// constructed file can't cause arbitrary code execution. As a result of all
// of this, we don't hint libbacktrace with the path to the current process.
unsafe fn init_state() -> *mut backtrace_state {
static mut STATE: *mut backtrace_state = ptr::null_mut();
static mut LAST_FILENAME: [libc::c_char; 256] = [0; 256];
if !STATE.is_null() { return STATE }
let selfname = if cfg!(target_os = "freebsd") ||
cfg!(target_os = "dragonfly") ||
cfg!(target_os = "bitrig") ||
cfg!(target_os = "openbsd") ||
cfg!(target_os = "windows") {
env::current_exe().ok()
} else {
None
};
let filename = match selfname.as_ref().and_then(|s| s.to_str()) {
Some(path) => {
let bytes = path.as_bytes();
if bytes.len() < LAST_FILENAME.len() {
let i = bytes.iter();
for (slot, val) in LAST_FILENAME.iter_mut().zip(i) {
*slot = *val as libc::c_char;
}
LAST_FILENAME.as_ptr()
} else {
ptr::null()
}
}
None => ptr::null(),
};
STATE = backtrace_create_state(filename, 0, error_cb,
STATE = backtrace_create_state(ptr::null(), 0, error_cb,
ptr::null_mut());
STATE
}
14 changes: 9 additions & 5 deletions src/test/run-pass/backtrace-debuginfo.rs
Original file line number Diff line number Diff line change
@@ -32,11 +32,15 @@ macro_rules! dump_and_die {
($($pos:expr),*) => ({
// FIXME(#18285): we cannot include the current position because
// the macro span takes over the last frame's file/line.
if cfg!(target_os = "macos") ||
cfg!(target_os = "ios") ||
cfg!(target_os = "android") ||
cfg!(all(target_os = "linux", target_arch = "arm")) ||
cfg!(all(windows, target_env = "gnu")) {
if cfg!(any(target_os = "macos",
target_os = "ios",
target_os = "android",
all(target_os = "linux", target_arch = "arm"),
target_os = "windows",
target_os = "freebsd",
target_os = "dragonfly",
target_os = "bitrig",
target_os = "openbsd")) {
// skip these platforms as this support isn't implemented yet.
} else {
dump_filelines(&[$($pos),*]);
2 changes: 1 addition & 1 deletion src/test/run-pass/backtrace.rs
Original file line number Diff line number Diff line change
@@ -115,7 +115,7 @@ fn runtest(me: &str) {
}

fn main() {
if cfg!(windows) && cfg!(target_arch = "x86") && cfg!(target_env = "gnu") {
if cfg!(windows) && cfg!(target_env = "gnu") {
return
}