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Re: [PATCH] Avoid accessing corrupted stack from __stack_chk_fail [BZ #21752]
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: GNU C Library <libc-alpha at sourceware dot org>
- Date: Mon, 24 Jul 2017 05:50:48 -0700
- Subject: Re: [PATCH] Avoid accessing corrupted stack from __stack_chk_fail [BZ #21752]
- Authentication-results: sourceware.org; auth=none
- References: <20170719185036.GA32763@gmail.com>
On Wed, Jul 19, 2017 at 11:50 AM, H.J. Lu <hongjiu.lu@intel.com> wrote:
> __libc_argv[0] points to address on stack and __libc_secure_getenv
> accesses environment variables which are on stack. We should avoid
> accessing stack when stack is corrupted.
>
> This patch also renames function argument in __fortify_fail_abort
> from do_backtrace to need_backtrace to avoid confusion with do_backtrace
> from enum __libc_message_action.
>
> Tested on x86-64 and i686. OK for master?
>
> H.J.
> ---
> [BZ #21752]
> * debug/fortify_fail.c (__fortify_fail_abort): Don't pass down
> __libc_argv[0] if we aren't doing backtrace. Rename do_backtrace
> to need_backtrace.
> * sysdeps/posix/libc_fatal.c (__libc_message): Don't call
> __libc_secure_getenv if we aren't doing backtrace.
> ---
> debug/fortify_fail.c | 12 ++++++++----
> sysdeps/posix/libc_fatal.c | 15 ++++++++++-----
> 2 files changed, 18 insertions(+), 9 deletions(-)
>
> diff --git a/debug/fortify_fail.c b/debug/fortify_fail.c
> index c90d384daf..a0777ae570 100644
> --- a/debug/fortify_fail.c
> +++ b/debug/fortify_fail.c
> @@ -24,13 +24,17 @@ extern char **__libc_argv attribute_hidden;
>
> void
> __attribute__ ((noreturn)) internal_function
> -__fortify_fail_abort (_Bool do_backtrace, const char *msg)
> +__fortify_fail_abort (_Bool need_backtrace, const char *msg)
> {
> - /* The loop is added only to keep gcc happy. */
> + /* The loop is added only to keep gcc happy. Don't pass down
> + __libc_argv[0] if we aren't doing backtrace since __libc_argv[0]
> + may point to the corrupted stack. */
> while (1)
> - __libc_message (do_backtrace ? (do_abort | do_backtrace) : do_abort,
> + __libc_message (need_backtrace ? (do_abort | do_backtrace) : do_abort,
> "*** %s ***: %s terminated\n",
> - msg, __libc_argv[0] ?: "<unknown>");
> + msg,
> + (need_backtrace && __libc_argv[0] != NULL
> + ? __libc_argv[0] : "<unknown>"));
> }
>
> void
> diff --git a/sysdeps/posix/libc_fatal.c b/sysdeps/posix/libc_fatal.c
> index 25af8bd413..c9189194dd 100644
> --- a/sysdeps/posix/libc_fatal.c
> +++ b/sysdeps/posix/libc_fatal.c
> @@ -75,11 +75,16 @@ __libc_message (enum __libc_message_action action, const char *fmt, ...)
> FATAL_PREPARE;
> #endif
>
> - /* Open a descriptor for /dev/tty unless the user explicitly
> - requests errors on standard error. */
> - const char *on_2 = __libc_secure_getenv ("LIBC_FATAL_STDERR_");
> - if (on_2 == NULL || *on_2 == '\0')
> - fd = open_not_cancel_2 (_PATH_TTY, O_RDWR | O_NOCTTY | O_NDELAY);
> + /* Don't call __libc_secure_getenv if we aren't doing backtrace, which
> + may access the corrupted stack. */
> + if ((action & do_backtrace))
> + {
> + /* Open a descriptor for /dev/tty unless the user explicitly
> + requests errors on standard error. */
> + const char *on_2 = __libc_secure_getenv ("LIBC_FATAL_STDERR_");
> + if (on_2 == NULL || *on_2 == '\0')
> + fd = open_not_cancel_2 (_PATH_TTY, O_RDWR | O_NOCTTY | O_NDELAY);
> + }
>
> if (fd == -1)
> fd = STDERR_FILENO;
> --
> 2.13.3
>
Any comments, objections?
Glibc should avoid accessing corrupted stack from __fortify_fail_abort,
which somewhat defeats the purpose of -fstack-protector.
--
H.J.