[patch 2/8] 2.6.22-rc4-mm2 buffered write fixes

[Nick Piggin <npiggin@suse.de>]

Dmitriy noticed that iov_iter_fault_in_readable could go past the end
of the first iov in a multi-iov situation, and that could be considered
an EFAULT by the caller. Fix and comment.

Fixes: fs-introduce-write_begin-write_end-and-perform_write-aops.patch

Signed-off-by: Nick Piggin <npiggin@suse.de>

Index: linux-2.6/mm/filemap.c
===================================================================
--- linux-2.6.orig/mm/filemap.c
+++ linux-2.6/mm/filemap.c
@@ -1794,9 +1794,19 @@ void iov_iter_advance(struct iov_iter *i
 	i->count -= bytes;
 }
 
+/*
+ * Fault in the first iovec of the given iov_iter, to a maximum length
+ * of bytes. Returns 0 on success, or non-zero if the memory could not be
+ * accessed (ie. because it is an invalid address).
+ *
+ * writev-intensive code may want this to prefault several iovecs -- that
+ * would be possible (callers must not rely on the fact that _only_ the
+ * first iovec will be faulted with the current implementation).
+ */
 int iov_iter_fault_in_readable(struct iov_iter *i, size_t bytes)
 {
 	char __user *buf = i->iov->iov_base + i->iov_offset;
+	bytes = min(bytes, i->iov->iov_len - i->iov_offset);
 	return fault_in_pages_readable(buf, bytes);
 }