setgid first, setuid second

Setting a new effective gid requires privileges.  We must set the gid
while we potentially still have superuser privileges.  Otherwise
setgid(2) fails because we've already changed to an unprivileged uid.

Here is a test case:
[global]
rw=read
directory=tmp
size=512m
buffered=0

[file1]
uid=1000
gid=1000

Without this patch fio will fail when invoked by root.

Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

diff --git a/fio.c b/fio.c
index 8dff813cc20bab39d7b1ac13d1ca0c80d611440a..8cc8fcf3361be69e39bd4003a8d93e8ec81466a2 100644 (file)
--- a/fio.c
+++ b/fio.c
@@ -1068,14 +1068,18 @@ static void *thread_main(void *data)
         */
        fio_mutex_remove(td->mutex);
 
-       if (td->o.uid != -1U && setuid(td->o.uid)) {
-               td_verror(td, errno, "setuid");
-               goto err;
-       }
+       /*
+        * A new gid requires privilege, so we need to do this before setting
+        * the uid.
+        */
        if (td->o.gid != -1U && setgid(td->o.gid)) {
                td_verror(td, errno, "setgid");
                goto err;
        }
+       if (td->o.uid != -1U && setuid(td->o.uid)) {
+               td_verror(td, errno, "setuid");
+               goto err;
+       }
 
        /*
         * May alter parameters that init_io_u() will use, so we need to