[PATCH] sys_set/getpriority PRIO_USER semantics fix and optimisation

[PATCH] sys_set/getpriority PRIO_USER semantics fix and optimisation

[pmeda]

This change brings the semantics equivalent to 2.4 and also to what
the man page says; Also optimises by avoiding unneeded lookup in uid
cache, when who is same as the current->uid.

sys_set/getpriority is rewritten in 2.5/2.6, perhaps while transitioning
to the pid maps.  It has now semantical bug, when uid is zero.  Note
that akpm also fixed refcount leak and locking in the new functions
in changeset http://linus.bkbits.net:8080/linux-2.5/cset@1.1608.10.84

 sys.c |   26 ++++++++++++--------------
 1 files changed, 12 insertions, 14 deletions


Signed-off-by: pmeda@akamai.com


--- linux-2.6.9-1/kernel/sys.c	Wed Dec  1 20:46:50 2004
+++ linux-2.6.9-2/kernel/sys.c	Wed Dec  1 21:47:36 2004
@@ -341,19 +341,18 @@
 			} while_each_task_pid(who, PIDTYPE_PGID, p);
 			break;
 		case PRIO_USER:
-			if (!who)
-				user = current->user;
-			else
-				user = find_user(who);
-
-			if (!user)
-				goto out_unlock;
+			user = current->user;
+			if (!who)
+				who = current->uid;
+			else 
+				if ((who != current->uid) && !(user = find_user(who)))
+					goto out_unlock;	/* No processes for this user */
 
 			do_each_thread(g, p)
 				if (p->uid == who)
 					error = set_one_prio(p, niceval, error);
 			while_each_thread(g, p);
-			if (who)
+			if (who != current->uid)
 				free_uid(user);		/* For find_user() */
 			break;
 	}
@@ -400,13 +399,12 @@
 			} while_each_task_pid(who, PIDTYPE_PGID, p);
 			break;
 		case PRIO_USER:
+			user = current->user;
 			if (!who)
-				user = current->user;
+				who = current->uid;
 			else
-				user = find_user(who);
-
-			if (!user)
-				goto out_unlock;
+				if ((who != current->uid) && !(user = find_user(who)))
+					goto out_unlock;	/* No processes for this user */
 
 			do_each_thread(g, p)
 				if (p->uid == who) {
@@ -415,7 +413,7 @@
 						retval = niceval;
 				}
 			while_each_thread(g, p);
-			if (who)
+			if (who != current->uid)
 				free_uid(user);		/* for find_user() */
 			break;
 	}

Re: [PATCH] sys_set/getpriority PRIO_USER semantics fix and optimisation

[Prasanna Meda]

pmeda@akamai.com wrote:

> sys_set/getpriority is rewritten in 2.5/2.6, perhaps while transitioning
> to the pid maps.  It has now semantical bug, when uid is zero.  Note

A test case:

#include <stdio.h>
#include <sys/time.h>
#include <sys/resource.h>

int main()
{
        int prio1, prio2, ret, errno;

        /* If root, loose priv. for testing */
        setresuid(237, 237, 237);

        prio1 = getpriority(2, getuid());
        if (setpriority(PRIO_USER, 0, prio1+1) < 0) {
                perror("setprio");
                printf("FAILED!\n");
        }
        else {
                prio2 = getpriority(2, getuid());
                printf("Old prio:%d to new prio:%d\n", prio1, prio2);
                printf((prio1 +1 != prio2)? "FAILED\n":"PASSED\n");
        }
        exit(0);
}