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Use the AT_SECURE auxv flag to determine whether to enable secure mode.

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The Linux kernel provides an AT_SECURE auxv flag to inform userspace
whether or not a security transition has occurred.  This is more reliable
than directly checking the uid/gid against the euid/egid, because it covers
not only setuid/setgid but also file capabilities, SELinux, and AppArmor
security transitions.  It is also a more efficient test since it does
not require any additional system calls.

Change-Id: I9752a4f6da452273258d2876d13b05e402fb0409
This commit is contained in:
Stephen Smalley 2012-01-13 07:48:11 -05:00
parent eae1f1fba3
commit 861b42a2d8
1 changed files with 15 additions and 4 deletions
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19
linker/linker.c
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@ -2085,7 +2085,7 @@ unsigned __linker_init(unsigned **elfdata)
int argc = (int) *elfdata;
char **argv = (char**) (elfdata + 1);
unsigned *vecs = (unsigned*) (argv + argc + 1);
unsigned *vecs = (unsigned*) (argv + argc + 1), *v;
soinfo *si;
struct link_map * map;
const char *ldpath_env = NULL;
@ -2113,12 +2113,23 @@ unsigned __linker_init(unsigned **elfdata)
*/
__tls_area[TLS_SLOT_BIONIC_PREINIT] = elfdata;
/* Are we setuid? */
program_is_setuid = (getuid() != geteuid()) || (getgid() != getegid());
/* Initialize environment functions, and get to the ELF aux vectors table */
vecs = linker_env_init(vecs);
/* Check auxv for AT_SECURE first to see if program is setuid, setgid,
has file caps, or caused a SELinux/AppArmor domain transition. */
for (v = vecs; v[0]; v += 2) {
if (v[0] == AT_SECURE) {
/* kernel told us whether to enable secure mode */
program_is_setuid = v[1];
goto sanitize;
}
}
/* Kernel did not provide AT_SECURE - fall back on legacy test. */
program_is_setuid = (getuid() != geteuid()) || (getgid() != getegid());
sanitize:
/* Sanitize environment if we're loading a setuid program */
if (program_is_setuid)
linker_env_secure();