[PATCH] uml: hostfs - fix possible PAGE_CACHE_SHIFT overflows

Prevent page->index << PAGE_CACHE_SHIFT from overflowing.

There is a casting there, but was added without care, so it's at the wrong
place. Note the extra parens around the shift - "+" is higher precedence than
"<<", leading to a GCC warning which saved all us.

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 6 insertions, 1 deletions

diff --git a/fs/hostfs/hostfs_kern.c b/fs/hostfs/hostfs_kern.c
index 3aac164c7726..b3ad0bd0312f 100644
--- a/fs/hostfs/hostfs_kern.c
+++ b/fs/hostfs/hostfs_kern.c
@@ -501,11 +501,16 @@ int hostfs_commit_write(struct file *file, struct page *page, unsigned from,
         long long start;
         int err = 0;
 
-        start = (long long) (page->index << PAGE_CACHE_SHIFT) + from;
+        start = (((long long) page->index) << PAGE_CACHE_SHIFT) + from;
         buffer = kmap(page);
         err = write_file(FILE_HOSTFS_I(file)->fd, &start, buffer + from,
                          to - from);
         if(err > 0) err = 0;
+
+        /* Actually, if !err, write_file has added to-from to start, so, despite
+         * the appearance, we are comparing i_size against the _last_ written
+         * location, as we should. */
+
         if(!err && (start > inode->i_size))
                 inode->i_size = start;