iov_iter_advance() fix

commit: f7009264c519603b8ec67c881bd368a56703cfc9

iov_iter_advance() skips over zero-length iovecs, however it does not properly
terminate at the end of the iovec array.  Fix this by checking against
i->count before we skip a zero-length iov.

The bug was reproduced with a test program that continually randomly creates
iovs to writev.  The fix was also verified with the same program and also it
could verify that the correct data was contained in the file after each
writev.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Tested-by: "Kevin Coffman" <kwc@citi.umich.edu>
Cc: "Alexey Dobriyan" <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/mm/filemap.c b/mm/filemap.c
index 69430d2dded294c5d38daf9d5b095b6a1fd80eae..76b036f983ad69d0f2d3619c4b168a03e2fee25b 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1725,21 +1725,27 @@ size_t iov_iter_copy_from_user(struct page *page,
 }
 EXPORT_SYMBOL(iov_iter_copy_from_user);
 
-static void __iov_iter_advance_iov(struct iov_iter *i, size_t bytes)
+void iov_iter_advance(struct iov_iter *i, size_t bytes)
 {
+       BUG_ON(i->count < bytes);
+
        if (likely(i->nr_segs == 1)) {
                i->iov_offset += bytes;
+               i->count -= bytes;
        } else {
                const struct iovec *iov = i->iov;
                size_t base = i->iov_offset;
 
                /*
                 * The !iov->iov_len check ensures we skip over unlikely
-                * zero-length segments.
+                * zero-length segments (without overruning the iovec).
                 */
-               while (bytes || !iov->iov_len) {
-                       int copy = min(bytes, iov->iov_len - base);
+               while (bytes || unlikely(!iov->iov_len && i->count)) {
+                       int copy;
 
+                       copy = min(bytes, iov->iov_len - base);
+                       BUG_ON(!i->count || i->count < copy);
+                       i->count -= copy;
                        bytes -= copy;
                        base += copy;
                        if (iov->iov_len == base) {
@@ -1751,14 +1757,6 @@ static void __iov_iter_advance_iov(struct iov_iter *i, size_t bytes)
                i->iov_offset = base;
        }
 }
-
-void iov_iter_advance(struct iov_iter *i, size_t bytes)
-{
-       BUG_ON(i->count < bytes);
-
-       __iov_iter_advance_iov(i, bytes);
-       i->count -= bytes;
-}
 EXPORT_SYMBOL(iov_iter_advance);
 
 /*