On 04/22/2016 04:41 PM, Olga Kornievskaia wrote:
> On Fri, Apr 22, 2016 at 2:38 PM, Steve Dickson <SteveD@xxxxxxxxxx> wrote:
>>
>>
>> On 04/20/2016 05:12 PM, 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 | 10 ++++++++--
>>> 1 file changed, 8 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/utils/gssd/gssd_proc.c b/utils/gssd/gssd_proc.c
>>> index 581a125..5d9a6db 100644
>>> --- a/utils/gssd/gssd_proc.c
>>> +++ b/utils/gssd/gssd_proc.c
>>> @@ -69,6 +69,7 @@
>>> #include <netdb.h>
>>> #include <sys/types.h>
>>> #include <sys/wait.h>
>>> +#include <syscall.h>
>>>
>>> #include "gssd.h"
>>> #include "err_util.h"
>>> @@ -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) {
>>> printerr(0, "WARNING: Failed to setuid for user with uid %u\n",
>>> uid);
>>> return errno;
>>>
>> We also have to do the same thing to the setgroups() call at the
>> top of change_identity(). So add the following diff to this
>> patch and we are good to go...
>>
>> diff --git a/utils/gssd/gssd_proc.c b/utils/gssd/gssd_proc.c
>> index e651d71..2f9f8ab 100644
>> --- a/utils/gssd/gssd_proc.c
>> +++ b/utils/gssd/gssd_proc.c
>> @@ -437,7 +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;
>> }
>>
>
> Do you know why we do this before getting the passwd entry?
It came in with commit 6b53fc9c which changed the way gssd
changed the uid/gid from Jeff Layton...
Jeff, what was the thought behind dropping supplementary groups?
I believe it was some type of security thing.
>
> Doing as you suggest causes problems as in it it fails to drop the
> supplementary groups.
hmm... what are you seeing that I'm not?
steved.
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