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[Bug libc/22625] RPATH $ORIGIN replaced by PWD for AT_SECURE/SUID binaries or if /proc is not mounted (CVE-2017-16997)
- From: "ldv at sourceware dot org" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sourceware dot org
- Date: Sun, 17 Dec 2017 20:23:45 +0000
- Subject: [Bug libc/22625] RPATH $ORIGIN replaced by PWD for AT_SECURE/SUID binaries or if /proc is not mounted (CVE-2017-16997)
- Auto-submitted: auto-generated
- References: <bug-22625-131@http.sourceware.org/bugzilla/>
https://sourceware.org/bugzilla/show_bug.cgi?id=22625
Dmitry V. Levin <ldv at sourceware dot org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |ldv at sourceware dot org
--- Comment #2 from Dmitry V. Levin <ldv at sourceware dot org> ---
(In reply to Aurelien Jarno from comment #1)
> The fillin_rpath function in elf/dl-load.c loops over each RPATH or RUNPATH
> tokens and interpret empty tokens as the current directory ("./"). In
> practice the check for empty token is done *after* the dynamic string token
> expansion. The expansion process can return an empty string for the $ORIGIN
> token if __libc_enable_secure is set or if the path of the binary can not be
> determined (/proc not mounted).
>
> In short it means that the dynamic linker can load libraries (including
> libc.so.6) from the current directory for AT_SECURE and SUID binaries that
> have an RPATH or RUNPATH starting with $ORIGIN.
Yes.
> Libraries with a $ORIGIN RPATH are handled correctly.
Sorry, did you mean "without $ORIGIN"?
> The bug exists since glibc 2.19.
>
> The test is as simple as:
> - echo 'int main() {}' > test.c
> - gcc test.c -Wl,-rpath,'$ORIGIN' -Wl,-z,origin
> - change the binary to SUID root
> - run it under strace to see it tries to load libc.so.6 from the current
> directory (try from different paths).
Invoking a SUID executable under strace effectively strips SUID unless strace
itself is SUID, which is unlikely.
Here is a simpler test:
$ ln -snf /dev/null libc.so.6 && rm -rf d && mkdir -m0700 d && cd d && echo
'int main(){}' |gcc -xc - -Wl,-rpath,'$ORIGIN' && chgrp -h another_group a.out
&& chmod 02710 a.out && cd .. && d/a.out
d/a.out: error while loading shared libraries: libc.so.6: file too short
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