Why does integer overflow sanitizer exits the program with zero exit code

Hi All,

With “-fsanitize=integer” flag, when an overflow is detected the program is terminated with zero exit code. But with “-fsanitize=address” flag, the program terminates with non-zero exit code. I think the address sanitizer behavior of non-zero exit code is more intuitive since the program did exit in error. Is there any reason integer overflow sanitizer exits the program with zero exit code?

Thanks,
Riyad

Hi All,

With "-fsanitize=integer" flag, when an overflow is detected the program
is terminated with zero exit code.

You can change this behavior by using env. var.
UBSAN_OPTIONS=halt_on_error=1

(Not sure if this is properly documented anywhere. Alexey? )

But with "-fsanitize=address" flag, the program terminates with non-zero
exit code. I think the address sanitizer behavior of non-zero exit code is
more intuitive since the program did exit in error. Is there any reason
integer overflow sanitizer exits the program with zero exit code?

One of the reasons, maybe:
Programs are more often ubsan-unclean than asan-unclean, and halting on
every ubsan message makes it harder to deploy the tool.

Thanks for the reply.

I am developing a fuzzer and interested to find overflows. Is there any way to detect when errors are detected? To explain more, I have instrumented the binary to see which functions are called in run-time. What are the functions that are called when overflow is detected? When these functions are called I will know overflow is detected.

Thanks for the reply.

I am developing a fuzzer and interested to find overflows.

So am I :slight_smile:
llvm.org/docs/LibFuzzer.html

Is there any way to detect when errors are detected? To explain more, I
have instrumented the binary to see which functions are called in run-time.
What are the functions that are called when overflow is detected? When
these functions are called I will know overflow is detected.

Hi All,

With "-fsanitize=integer" flag, when an overflow is detected the program
is terminated with zero exit code.

You can change this behavior by using env. var.
UBSAN_OPTIONS=halt_on_error=1

I've tried this; didn't work.

What exactly do you run?

Here is what works for me:

% cat int-overflow.c
#include <stdio.h>
int x;
int main(int argc, char **argv) {
  x += 1 << 30;
  x += 1 << 30;
  printf("%d\n", x);
  return 0;
}

% clang -fsanitize=signed-integer-overflow int-overflow.c && ./a.out ; echo
EXIT STATUS: $?
int-overflow.c:5:5: runtime error: signed integer overflow: 1073741824 +
1073741824 cannot be represented in type 'int'
-2147483648
EXIT STATUS: 0
% clang -fsanitize=signed-integer-overflow int-overflow.c &&
UBSAN_OPTIONS=halt_on_error=1 ./a.out ; echo EXIT STATUS: $?
int-overflow.c:5:5: runtime error: signed integer overflow: 1073741824 +
1073741824 cannot be represented in type 'int'
EXIT STATUS: 1
%

Thanks! It works on the latest version of clang, but I was using clang 3.4 where it didn’t work.

On a more related note, SIGABRT better indicator of bugs than non-zero exit status. So I’ve tried “ASAN_OPTIONS=abort_on_error=1” option which works for address sanitizer where program exists with SIGABRT. But “UBSAN_OPTIONS=abort_on_error=1” doesn’t exit with SIGABRT. Is there any way to make overflow sanitizer exit with SIGABRT similar to address sanitizer?

Thanks! It works on the latest version of clang, but I was using clang 3.4
where it didn't work.

3.4 was loooong ago.

On a more related note, SIGABRT better indicator of bugs than non-zero
exit status. So I've tried "ASAN_OPTIONS=abort_on_error=1" option which
works for address sanitizer where program exists with SIGABRT. But
"UBSAN_OPTIONS=abort_on_error=1" doesn't exit with SIGABRT. Is there any
way to make overflow sanitizer exit with SIGABRT similar to address
sanitizer?

Just checked:

% clang -fsanitize=address,signed-integer-overflow int-overflow.c &&
UBSAN_OPTIONS=halt_on_error=1:abort_on_error=1 ./a.out ; echo EXIT STATUS:
$?
int-overflow.c:5:5: runtime error: signed integer overflow: 1073741824 +
1073741824 cannot be represented in type 'int'
SUMMARY: AddressSanitizer: undefined-behavior int-overflow.c:5:5 in
Aborted (core dumped)
EXIT STATUS: 134

Interesting! “UBSAN_OPTIONS=halt_on_error=1:abort_on_error=1” works fine, but just “UBSAN_OPTIONS=abort_on_error=1” doesn’t work. Is it by design?

Interesting! "UBSAN_OPTIONS=halt_on_error=1:abort_on_error=1" works fine,
but just "UBSAN_OPTIONS=abort_on_error=1" doesn't work. Is it by design?

sort of.
by default, ubsan simply does not exit, so it does not care about
abort_on_error.

Thanks a lot.

I had decided to detect overflow by SIGABRT. The issue SIGABRT is also thorwn by when assertion violation occurs. So SIGABRT is not the perfect indicator of overflow.

I see all the arithmetic operations are performed by “_ubsan_handle_overflow" built-in functions. If I catch SIGABRT, "_ubsan_handle_overflow” functions in the stack, can I safely assume the program is terminated in overflow?

Thanks,
Riyad

Thanks a lot.

I had decided to detect overflow by SIGABRT. The issue SIGABRT is also
thorwn by when assertion violation occurs. So SIGABRT is not the perfect
indicator of overflow.

I see all the arithmetic operations are performed by
"__ubsan_handle_*_overflow" built-in functions. If I catch SIGABRT,
"__ubsan_handle_*_overflow" functions in the stack, can I safely assume the
program is terminated in overflow?

Probably yes: if one of these function was called by the program, it will
certainly report an overflow. In theory, we don't guarantee that the names
of these functions will stay the same, or that we always report overflows
through them (i.e. it's an implementation detail), but in practice it would
unlikely change soon.

Is it possible to enable integer overflow sanitizer for certain cases as in many cases integer overflows are benign? I’m interested in mainly integer overflow during pointer arithmetic or memory allocations. Or enabling sanitizer for certain course files?

Thanks,Riyad

Can you please give an example of a benign integer overflow?
Note that by disabling the checks for non-pointer arithmetic you can easily throw the baby out with the bathwater. The compiler can easily take advantage of signed integer overflow being undefined irrespective of it being called “benign” or not.

Intuitively, one may indeed think that some signed integer overflows are more dangerous than others.
But scientifically, they are all bugs.
My favorite real-life example: http://stackoverflow.com/questions/7682477/why-does-integer-overflow-on-x86-with-gcc-cause-an-infinite-loop

It is totally unclear if we can come up with a reliable heuristic that will distinguish between less harmful and more harmful int overflows.
E.g. what if the computation of an array index happens in a separate function?

–kcc

Intuitively, one may indeed think that some signed integer overflows are
more dangerous than others.
But scientifically, they are all bugs.

I agree, they are all bugs unless someone using overflows for optimizing
code. But from security perspective not all bugs are security
vulnerabilities. Right now I'm interested into security vulnerabilities
only.

My favorite real-life example:

http://stackoverflow.com/questions/7682477/why-does-integer-overflow-on-x86-with-gcc-cause-an-infinite-loop

It is totally unclear if we can come up with a reliable heuristic that
will distinguish between less harmful and more harmful int overflows.
E.g. what if the computation of an array index happens in a separate
function?

In academic security research, what I've seen so far is that dynamic taint
analysis is done with conjunction with overflow checks. If the operands in
overflows are tainted by user input and that arithmetic overflow leads to
crashes etc. i.e., an user has the ability to crash the program by simply
providing different kinds of input, then it's more interesting. But again,
things are not that simple. Overflows can change the intended semantics of
the program which in turn can lead to security vulnerabilities.

Coming back to the original question, is there any API or option to enable
overflow checks for certain translation units?

--kcc

Intuitively, one may indeed think that some signed integer overflows are
more dangerous than others.
But scientifically, they are all bugs.

I agree, they are all bugs unless someone using overflows for optimizing
code. But from security perspective not all bugs are security
vulnerabilities. Right now I'm interested into security vulnerabilities
only.

My favorite real-life example:

http://stackoverflow.com/questions/7682477/why-does-integer-overflow-on-x86-with-gcc-cause-an-infinite-loop

It is totally unclear if we can come up with a reliable heuristic that
will distinguish between less harmful and more harmful int overflows.
E.g. what if the computation of an array index happens in a separate
function?

In academic security research, what I've seen so far is that dynamic taint
analysis is done with conjunction with overflow checks. If the operands in
overflows are tainted by user input and that arithmetic overflow leads to
crashes etc. i.e., an user has the ability to crash the program by simply
providing different kinds of input, then it's more interesting. But again,
things are not that simple. Overflows can change the intended semantics of
the program which in turn can lead to security vulnerabilities.

Coming back to the original question, is there any API or option to enable
overflow checks for certain translation units?

You can do this by simply adding -fsanitize=* to the units you want to
check and not adding it to others.
You can also use -fsanitize-blacklist=blacklist.txt, see
http://clang.llvm.org/docs/SanitizerSpecialCaseList.html