From: David Teigland <teigland@redhat.com>
Date: Wed, 4 Mar 2009 11:42:11 -0600
Subject: [dlm] fix length calculation in compat code
Message-id: 20090304174211.GA30629@redhat.com
O-Subject: [RHEL5.4 PATCH] dlm: fix length calculation in compat code
Bugzilla: 487672

bz 487672 - slab corruption with dlm and clvmd on ppc64

brew build including this patch
https://brewweb.devel.redhat.com/taskinfo?taskID=1712570

upstream: in linux-next pending 2.6.30 merge

Using offsetof() to calculate name length does not work because
it does not produce consistent results with with structure packing.
This caused memcpy to corrupt memory by copying 4 extra bytes off
the end of the buffer on 64 bit kernels with 32 bit userspace
(the only case where this 32/64 compat code is used).

Also make sure that the name string is nil terminated, which was
the intent of the original patch (bz 458760) that replaced strcpy
with memcpy and offsetof.

Signed-off-by: David Teigland <teigland@redhat.com>

diff --git a/fs/dlm/user.c b/fs/dlm/user.c
index 302cf0c..e219e53 100644
--- a/fs/dlm/user.c
+++ b/fs/dlm/user.c
@@ -84,7 +84,7 @@ struct dlm_lock_result32 {
 
 static void compat_input(struct dlm_write_request *kb,
 			 struct dlm_write_request32 *kb32,
-			 size_t count)
+			 int namelen)
 {
 	kb->version[0] = kb32->version[0];
 	kb->version[1] = kb32->version[1];
@@ -96,8 +96,7 @@ static void compat_input(struct dlm_write_request *kb,
 	    kb->cmd == DLM_USER_REMOVE_LOCKSPACE) {
 		kb->i.lspace.flags = kb32->i.lspace.flags;
 		kb->i.lspace.minor = kb32->i.lspace.minor;
-		memcpy(kb->i.lspace.name, kb32->i.lspace.name, count -
-		       offsetof(struct dlm_write_request32, i.lspace.name));
+		memcpy(kb->i.lspace.name, kb32->i.lspace.name, namelen);
 	} else if (kb->cmd == DLM_USER_PURGE) {
 		kb->i.purge.nodeid = kb32->i.purge.nodeid;
 		kb->i.purge.pid = kb32->i.purge.pid;
@@ -115,8 +114,7 @@ static void compat_input(struct dlm_write_request *kb,
 		kb->i.lock.bastaddr = (void *)(long)kb32->i.lock.bastaddr;
 		kb->i.lock.lksb = (void *)(long)kb32->i.lock.lksb;
 		memcpy(kb->i.lock.lvb, kb32->i.lock.lvb, DLM_USER_LVB_LEN);
-		memcpy(kb->i.lock.name, kb32->i.lock.name, count -
-		       offsetof(struct dlm_write_request32, i.lock.name));
+		memcpy(kb->i.lock.name, kb32->i.lock.name, namelen);
 	}
 }
 
@@ -525,15 +523,25 @@ static ssize_t device_write(struct file *file, const char __user *buf,
 #ifdef CONFIG_COMPAT
 	if (!kbuf->is64bit) {
 		struct dlm_write_request32 *k32buf;
+		int namelen = 0;
+
+		if (count > sizeof(struct dlm_write_request32))
+			namelen = count - sizeof(struct dlm_write_request32);
+
 		k32buf = (struct dlm_write_request32 *)kbuf;
-		kbuf = kmalloc(count + 1 + (sizeof(struct dlm_write_request) -
-			       sizeof(struct dlm_write_request32)), GFP_KERNEL);
-		if (!kbuf)
+
+		/* add 1 after namelen so that the name string is terminated */
+		kbuf = kzalloc(sizeof(struct dlm_write_request) + namelen + 1,
+			       GFP_KERNEL);
+		if (!kbuf) {
+			kfree(k32buf);
 			return -ENOMEM;
+		}
 
 		if (proc)
 			set_bit(DLM_PROC_FLAGS_COMPAT, &proc->flags);
-		compat_input(kbuf, k32buf, count + 1);
+
+		compat_input(kbuf, k32buf, namelen);
 		kfree(k32buf);
 	}
 #endif