[PATCH] Fix the size limit of compat space msgsize

Currently we allocate 64k space on the user stack and use it the msgbuf for
sys_{msgrcv,msgsnd} for compat and the results are later copied in user [
by copy_in_user].  This patch introduces helper routines for
sys_{msgrcv,msgsnd} as below:

do_msgsnd() : Accepts the mtype and user space ptr to the buffer along with
the msqid and msgflg.

do_msgrcv() : Accepts a kernel space ptr to mtype and a userspace ptr to
the buffer.  The mtype has to be copied back the user space msgbuf by the
caller.

These changes avoid the need to allocate the msgsize on the userspace (
thus removing the size limt ) and the overhead of an extra copy_in_user().

Signed-off-by: Suzuki K P <suzuki@in.ibm.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/linux/msg.h

@@ -92,6 +92,12 @@ struct msg_queue {
 	struct list_head q_senders;
 };
 
+/* Helper routines for sys_msgsnd and sys_msgrcv */
+extern long do_msgsnd(int msqid, long mtype, void __user *mtext,
+			size_t msgsz, int msgflg);
+extern long do_msgrcv(int msqid, long *pmtype, void __user *mtext,
+			size_t msgsz, long msgtyp, int msgflg);
+
 #endif /* __KERNEL__ */
 
 #endif /* _LINUX_MSG_H */

ipc/compat.c

@@ -115,7 +115,6 @@ struct compat_shm_info {
 
 extern int sem_ctls[];
 #define sc_semopm	(sem_ctls[2])
-#define MAXBUF (64*1024)
 
 static inline int compat_ipc_parse_version(int *cmd)
 {
@@ -307,35 +306,30 @@ long compat_sys_semctl(int first, int second, int third, void __user *uptr)
 
 long compat_sys_msgsnd(int first, int second, int third, void __user *uptr)
 {
-	struct msgbuf __user *p;
 	struct compat_msgbuf __user *up = uptr;
 	long type;
 
 	if (first < 0)
 		return -EINVAL;
-	if (second < 0 || (second >= MAXBUF - sizeof(struct msgbuf)))
+	if (second < 0)
 		return -EINVAL;
 
-	p = compat_alloc_user_space(second + sizeof(struct msgbuf));
-	if (get_user(type, &up->mtype) ||
-	    put_user(type, &p->mtype) ||
-	    copy_in_user(p->mtext, up->mtext, second))
+	if (get_user(type, &up->mtype))
 		return -EFAULT;
 
-	return sys_msgsnd(first, p, second, third);
+	return do_msgsnd(first, type, up->mtext, second, third);
 }
 
 long compat_sys_msgrcv(int first, int second, int msgtyp, int third,
 			   int version, void __user *uptr)
 {
-	struct msgbuf __user *p;
 	struct compat_msgbuf __user *up;
 	long type;
 	int err;
 
 	if (first < 0)
 		return -EINVAL;
-	if (second < 0 || (second >= MAXBUF - sizeof(struct msgbuf)))
+	if (second < 0)
 		return -EINVAL;
 
 	if (!version) {
@@ -349,14 +343,11 @@ long compat_sys_msgrcv(int first, int second, int msgtyp, int third,
 		uptr = compat_ptr(ipck.msgp);
 		msgtyp = ipck.msgtyp;
 	}
-	p = compat_alloc_user_space(second + sizeof(struct msgbuf));
-	err = sys_msgrcv(first, p, second, msgtyp, third);
+	up = uptr;
+	err = do_msgrcv(first, &type, up->mtext, second, msgtyp, third);
 	if (err < 0)
 		goto out;
-	up = uptr;
-	if (get_user(type, &p->mtype) ||
-	    put_user(type, &up->mtype) ||
-	    copy_in_user(up->mtext, p->mtext, err))
+	if (put_user(type, &up->mtype))
 		err = -EFAULT;
 out:
 	return err;

ipc/msg.c

@@ -626,12 +626,11 @@ static inline int pipelined_send(struct msg_queue *msq, struct msg_msg *msg)
 	return 0;
 }
 
-asmlinkage long
-sys_msgsnd(int msqid, struct msgbuf __user *msgp, size_t msgsz, int msgflg)
+long do_msgsnd(int msqid, long mtype, void __user *mtext,
+		size_t msgsz, int msgflg)
 {
 	struct msg_queue *msq;
 	struct msg_msg *msg;
-	long mtype;
 	int err;
 	struct ipc_namespace *ns;
 
@@ -639,12 +638,10 @@ sys_msgsnd(int msqid, struct msgbuf __user *msgp, size_t msgsz, int msgflg)
 
 	if (msgsz > ns->msg_ctlmax || (long) msgsz < 0 || msqid < 0)
 		return -EINVAL;
-	if (get_user(mtype, &msgp->mtype))
-		return -EFAULT;
 	if (mtype < 1)
 		return -EINVAL;
 
-	msg = load_msg(msgp->mtext, msgsz);
+	msg = load_msg(mtext, msgsz);
 	if (IS_ERR(msg))
 		return PTR_ERR(msg);
 
@@ -723,6 +720,16 @@ out_free:
 	return err;
 }
 
+asmlinkage long
+sys_msgsnd(int msqid, struct msgbuf __user *msgp, size_t msgsz, int msgflg)
+{
+	long mtype;
+
+	if (get_user(mtype, &msgp->mtype))
+		return -EFAULT;
+	return do_msgsnd(msqid, mtype, msgp->mtext, msgsz, msgflg);
+}
+
 static inline int convert_mode(long *msgtyp, int msgflg)
 {
 	/*
@@ -742,8 +749,8 @@ static inline int convert_mode(long *msgtyp, int msgflg)
 	return SEARCH_EQUAL;
 }
 
-asmlinkage long sys_msgrcv(int msqid, struct msgbuf __user *msgp, size_t msgsz,
-			   long msgtyp, int msgflg)
+long do_msgrcv(int msqid, long *pmtype, void __user *mtext,
+		size_t msgsz, long msgtyp, int msgflg)
 {
 	struct msg_queue *msq;
 	struct msg_msg *msg;
@@ -889,15 +896,30 @@ out_unlock:
 		return PTR_ERR(msg);
 
 	msgsz = (msgsz > msg->m_ts) ? msg->m_ts : msgsz;
-	if (put_user (msg->m_type, &msgp->mtype) ||
-	    store_msg(msgp->mtext, msg, msgsz)) {
+	*pmtype = msg->m_type;
+	if (store_msg(mtext, msg, msgsz))
 		msgsz = -EFAULT;
-	}
+
 	free_msg(msg);
 
 	return msgsz;
 }
 
+asmlinkage long sys_msgrcv(int msqid, struct msgbuf __user *msgp, size_t msgsz,
+			   long msgtyp, int msgflg)
+{
+	long err, mtype;
+
+	err =  do_msgrcv(msqid, &mtype, msgp->mtext, msgsz, msgtyp, msgflg);
+	if (err < 0)
+		goto out;
+
+	if (put_user(mtype, &msgp->mtype))
+		err = -EFAULT;
+out:
+	return err;
+}
+
 #ifdef CONFIG_PROC_FS
 static int sysvipc_msg_proc_show(struct seq_file *s, void *it)
 {