vfs: ensure page symlinks are NUL-terminated

On-disk data corruption could cause a page link to have its i_size set
to PAGE_SIZE (or a multiple thereof) and its contents all non-NUL.
NUL-terminate the link name to ensure this doesn't cause further
problems for the kernel.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Duane Griffin <duaneg@dghda.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 5 insertions, 2 deletions

diff --git a/fs/namei.c b/fs/namei.c
index ab441af4196b..9ed5e2818f80 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2786,13 +2786,16 @@ int vfs_follow_link(struct nameidata *nd, const char *link)
 /* get the link contents into pagecache */
 static char *page_getlink(struct dentry * dentry, struct page **ppage)
 {
-        struct page * page;
+        char *kaddr;
+        struct page *page;
         struct address_space *mapping = dentry->d_inode->i_mapping;
         page = read_mapping_page(mapping, 0, NULL);
         if (IS_ERR(page))
                 return (char*)page;
         *ppage = page;
-        return kmap(page);
+        kaddr = kmap(page);
+        nd_terminate_link(kaddr, dentry->d_inode->i_size, PAGE_SIZE - 1);
+        return kaddr;
 }
 
 int page_readlink(struct dentry *dentry, char __user *buffer, int buflen)