Avoid reading past buffer when calling GETACL

Bug noticed in commit
bf118a342f10dafe44b14451a1392c3254629a1f

When calling GETACL, if the size of the bitmap array, the length
attribute and the acl returned by the server is greater than the
allocated buffer(args.acl_len), we can Oops with a General Protection
fault at _copy_from_pages() when we attempt to read past the pages
allocated.

This patch allocates an extra PAGE for the bitmap and checks to see that
the bitmap + attribute_length + ACLs don't exceed the buffer space
allocated to it.

Signed-off-by: Sachin Prabhu <sprabhu@redhat.com>
Reported-by: Jian Li <jiali@redhat.com>
[Trond: Fixed a size_t vs unsigned int printk() warning]
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 10 insertions, 6 deletions

diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 60d5f4c26dda..f5f125fdae1b 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -3684,19 +3684,23 @@ static ssize_t __nfs4_get_acl_uncached(struct inode *inode, void *buf, size_t bu
 	if (npages == 0)
 		npages = 1;
 
+	/* Add an extra page to handle the bitmap returned */
+	npages++;
+
 	for (i = 0; i < npages; i++) {
 		pages[i] = alloc_page(GFP_KERNEL);
 		if (!pages[i])
 			goto out_free;
 	}
-	if (npages > 1) {
-		/* for decoding across pages */
-		res.acl_scratch = alloc_page(GFP_KERNEL);
-		if (!res.acl_scratch)
-			goto out_free;
-	}
+
+	/* for decoding across pages */
+	res.acl_scratch = alloc_page(GFP_KERNEL);
+	if (!res.acl_scratch)
+		goto out_free;
+
 	args.acl_len = npages * PAGE_SIZE;
 	args.acl_pgbase = 0;
+
 	/* Let decode_getfacl know not to fail if the ACL data is larger than
 	 * the page we send as a guess */
 	if (buf == NULL)