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-rw-r--r--mm/filemap.h26
1 files changed, 18 insertions, 8 deletions
diff --git a/mm/filemap.h b/mm/filemap.h
index 5683cde22055..536979fb4ba7 100644
--- a/mm/filemap.h
+++ b/mm/filemap.h
@@ -16,15 +16,23 @@
#include <linux/uaccess.h>
size_t
-__filemap_copy_from_user_iovec(char *vaddr,
- const struct iovec *iov,
- size_t base,
- size_t bytes);
+__filemap_copy_from_user_iovec_inatomic(char *vaddr,
+ const struct iovec *iov,
+ size_t base,
+ size_t bytes);
/*
* Copy as much as we can into the page and return the number of bytes which
* were sucessfully copied. If a fault is encountered then clear the page
* out to (offset+bytes) and return the number of bytes which were copied.
+ *
+ * NOTE: For this to work reliably we really want copy_from_user_inatomic_nocache
+ * to *NOT* zero any tail of the buffer that it failed to copy. If it does,
+ * and if the following non-atomic copy succeeds, then there is a small window
+ * where the target page contains neither the data before the write, nor the
+ * data after the write (it contains zero). A read at this time will see
+ * data that is inconsistent with any ordering of the read and the write.
+ * (This has been detected in practice).
*/
static inline size_t
filemap_copy_from_user(struct page *page, unsigned long offset,
@@ -60,13 +68,15 @@ filemap_copy_from_user_iovec(struct page *page, unsigned long offset,
size_t copied;
kaddr = kmap_atomic(page, KM_USER0);
- copied = __filemap_copy_from_user_iovec(kaddr + offset, iov,
- base, bytes);
+ copied = __filemap_copy_from_user_iovec_inatomic(kaddr + offset, iov,
+ base, bytes);
kunmap_atomic(kaddr, KM_USER0);
if (copied != bytes) {
kaddr = kmap(page);
- copied = __filemap_copy_from_user_iovec(kaddr + offset, iov,
- base, bytes);
+ copied = __filemap_copy_from_user_iovec_inatomic(kaddr + offset, iov,
+ base, bytes);
+ if (bytes - copied)
+ memset(kaddr + offset + copied, 0, bytes - copied);
kunmap(page);
}
return copied;