> On Apr 25, 2016, at 4:23 PM, Jeff Layton <jlayton@xxxxxxxxxxxxxxx> wrote:
>
> 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…
Thanks Jeff. Will fix that. setgroups take 2 args so that should be fixed too.
>> printerr(0, "WARNING: Failed to setuid for user with
> uid %u\n",
>> uid);
>> return errno;
> --
> Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
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