> On Apr 27, 2016, at 10:13 AM, Jeff Layton <jlayton@xxxxxxxxxxxxxxx> wrote:
>
> On Wed, 2016-04-27 at 10:09 -0400, Olga Kornievskaia wrote:
>> On Tue, Apr 26, 2016 at 12:51 PM, Jeff Layton <jlayton@xxxxxxxxxxxxxx
>> t> wrote:
>>> On Tue, 2016-04-26 at 09:34 -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..39c4b17 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) != 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, -1, -1) != 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, -1, -1) != 0) {
>>>> printerr(0, "WARNING: Failed to setuid for user
>>>> with uid %u\n",
>>>> uid);
>>>> return errno;
>>>
>>> Note that the old code set both real and effective uid/gid. Here
>>> you're
>>> changing it to just set the real uid. Is that change deliberate? I
>>> think you probably want to set the euid/egid as well.
>>
>> It was a typo (cthon tests ran fine though which is confusing since
>> kerberos code does geteuid()). Now I'm thinking that given that we
>> don't touch saved uid, perhaps the code should call SYS_setreuid
>> instead of SYS_setresuid?
>>
>
> Yes, good point. Either that or just set all 3 to "uid", I'd think.
There is a comment above saying leaving save-set-uid alone prevents ptrace from tracing us? Do we still care about this? ptrace wiki says that a kernel can be preconfigured to prevent ptrace from attaching to anything other than the traced process’ parent (that should address the comment).
>
> --
> Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
��.n��������+%������w��{.n�����{��w��� jg��� �����ݢj����G���� ���j:+v���w�m������w�������h�����٥
