On 04/27/2016 11:01 AM, Kornievskaia, Olga wrote:
>
>> 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).
I would guess not...
steved.
>
>>
>> --
>> Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
>
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