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security hardening: ensure suid programs have valid stdin/out/err

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this behavior (opening fds 0-2 for a suid program) is explicitly
allowed (but not required) by POSIX to protect badly-written suid
programs from clobbering files they later open.

this commit does add some cost in startup code, but the availability
of auxv and the security flag will be useful elsewhere in the future.
in particular auxv is needed for static-linked vdso support, which is
still waiting to be committed (sorry nik!)
This commit is contained in:
Rich Felker
2011-08-23 09:37:39 -04:00
parent c0f344160d
commit df0b5a4940
6 changed files with 52 additions and 15 deletions
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18
src/env/__libc_start_main.c vendored
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@ -1,21 +1,21 @@
#include "libc.h"
/* Any use of __environ/environ will override this symbol. */
char **__dummy_environ = (void *)-1;
weak_alias(__dummy_environ, ___environ);
void __init_security(size_t *);
int __libc_start_main(
int (*main)(int, char **, char **), int argc, char **argv,
int (*init)(int, char **, char **), void (*fini)(void),
void (*ldso_fini)(void))
{
/* Save the environment if it may be used by libc/application */
char **envp = argv+argc+1;
if (___environ != (void *)-1) ___environ = envp;
char **envp = argv+argc+1, **auxv = envp;
/* Avoid writing 0 and triggering unnecessary COW */
if (ldso_fini) libc.ldso_fini = ldso_fini;
if (fini) libc.fini = fini;
__environ = envp;
do auxv++; while (*auxv);
libc.auxv = (void *)++auxv;
libc.ldso_fini = ldso_fini;
libc.fini = fini;
__init_security((void *)auxv);
/* Execute constructors (static) linked into the application */
if (init) init(argc, argv, envp);