On Mon, 2016-04-25 at 12:58 -0400, Olga Kornievskaia wrote:
> For the threaded version we have to set uid,gid per thread instead
> of per process. glibc setresuid() when called from a thread, it'll
> send a signal to all other threads to synchronize the uid in all
> other threads. To bypass this, we have to call syscall() directly.
>
> Signed-off-by: Olga Kornievskaia <kolga@xxxxxxxxxx>
> Reviewed-by: Steve Dickson <steved@xxxxxxxxxx>
> ---
> utils/gssd/gssd_proc.c | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/utils/gssd/gssd_proc.c b/utils/gssd/gssd_proc.c
> index e2e95dc..487a4f5 100644
> --- a/utils/gssd/gssd_proc.c
> +++ b/utils/gssd/gssd_proc.c
> @@ -69,6 +69,7 @@
> #include
> #include
> #include
> +#include
>
> #include "gssd.h"
> #include "err_util.h"
> @@ -436,7 +437,7 @@ change_identity(uid_t uid)
> struct passwd *pw;
>
> /* drop list of supplimentary groups first */
> - if (setgroups(0, NULL) != 0) {
> + if (syscall(SYS_setgroups, 0) != 0) {
> printerr(0, "WARNING: unable to drop supplimentary groups!");
> return errno;
> }
> @@ -457,7 +458,12 @@ change_identity(uid_t uid)
> * Switch the GIDs. Note that we leave the saved-set-gid alone in an
> * attempt to prevent attacks via ptrace()
> */
> - if (setresgid(pw->pw_gid, pw->pw_gid, -1) != 0) {
> + /* For the threaded version we have to set uid,gid per thread instead
> + * of per process. glibc setresuid() when called from a thread, it'll
> + * send a signal to all other threads to synchronize the uid in all
> + * other threads. To bypass this, we have to call syscall() directly.
> + */
> + if (syscall(SYS_setresgid, pw->pw_gid) != 0) {
> printerr(0, "WARNING: failed to set gid to %u!\n", pw->pw_gid);
> return errno;
> }
> @@ -466,7 +472,7 @@ change_identity(uid_t uid)
> * Switch UIDs, but leave saved-set-uid alone to prevent ptrace() by
> * other processes running with this uid.
> */
> - if (setresuid(uid, uid, -1) != 0) {
> + if (syscall(SYS_setresuid, uid) != 0) {
That looks wrong. setresuid takes 3 arguments:
SYSCALL_DEFINE3(setresuid, uid_t, ruid, uid_t, euid, uid_t, suid)
Ditto for setresgid above. syscall is a varargs function, so you really
_must_ pass in the right number of args or you'll end up feeding it
random junk in registers or off the stack. The compiler won't save you
here...
> printerr(0, "WARNING: Failed to setuid for user with
uid %u\n",
> uid);
> return errno;
--
Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
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