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?
Doing as you suggest causes problems as in it it fails to drop the
supplementary groups.
> steved.
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