Re: Glibc - CVE-2015-8985 help

[Raluca-Petronela Florea <florea.raluca.petronela@gmail.com>]

Thanks a lot, I appreciate your help!
I read your answer and I understood!

On Tue, 5 May 2020, 13:46 Raluca-Petronela Florea, <
florea.raluca.petronela@gmail.com> wrote:

> Ok, thanks for clarification.
>
> So, do you have any idea how the regexp should look like in order to
> reproduce the issue from bug?
>
> Thank you very much!
>
> On Tue, 5 May 2020, 13:24 Aurelien Jarno, <aurelien@aurel32.net> wrote:
>
>> Hi,
>>
>> On 2020-05-05 12:14, Raluca-Petronela Florea wrote:
>> > Hello,
>> >
>> > I'm working on fixing some GLIBC vulnerabilities and I have an issue
>> > regarding
>> > CVE-2015-8985 - Assertion failure in pop_fail_stack when executing a
>> > malformed regexp
>> >
>> > Although it seems to be fixed in glibc 2.28, I've encountered the
>> following
>> > issue testing on a Ubuntu 19.10 virtual machine with glibc
>> 2.30-0ubuntu.2.1
>> > the following program:
>> >
>> > pop_fail_stack.c
>> >
>> > #include <assert.h>
>> > #include <regex.h>
>> > #include <stdio.h>
>> >
>> > int main(int argc, char **argv)
>> > {
>> >     int rc;
>> >     regex_t preg;
>> >     regmatch_t pmatch[2];
>> >
>> >     rc = regcomp(&preg, "()*)|\\1)*", REG_EXTENDED);
>> >     assert(rc == 0);
>> >     regexec(&preg, "", 2, pmatch, 0);
>> >     regfree(&preg);
>> >     return 0;
>> > }
>> >
>> > *pop_fail_stack: pop_fail_stack.c:12: main: Assertion `rc == 0' failed.*
>> > *Aborted (core dumped)*
>>
>> It means you glibc has the fix. The regex is clearly invalid so it
>> regcomp correctly fails to compile it.
>>
>> > As describes the Debian bug
>> > (https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=779392), the test
>> > program compiles an invalid regexp and then tries to match a string
>> > against it, triggers an assertion:
>> >
>> > *pop_fail_stack: regexec.c:1401: pop_fail_stack: Assertion `num >= 0'
>> failed.
>> > Aborted*
>>
>> That error message means the glibc is not fixed, i.e. regcomp is wronglu
>> able to compile it and regexec later triggers an assertion inside glibc
>> code.
>>
>> > So, in my scenario, the test program does not even successfully
>> > compile the invalid regexp.
>>
>> This is normal as the regexp is invalid, so it can't be compiled.
>>
>> Regards,
>> Aurelien
>>
>> --
>> Aurelien Jarno                          GPG: 4096R/1DDD8C9B
>> aurelien@aurel32.net                 http://www.aurel32.net
>>
>