4 files changed, 40 insertions, 26 deletions

diff --git a/fs/ntfs/file.c b/fs/ntfs/file.c
index 88292f9e4b9b..2e42c2dcae12 100644
--- a/fs/ntfs/file.c
+++ b/fs/ntfs/file.c
@@ -1358,7 +1358,7 @@ err_out:
         goto out;
 }
 
-static size_t __ntfs_copy_from_user_iovec(char *vaddr,
+static size_t __ntfs_copy_from_user_iovec_inatomic(char *vaddr,
                 const struct iovec *iov, size_t iov_ofs, size_t bytes)
 {
         size_t total = 0;
@@ -1376,10 +1376,6 @@ static size_t __ntfs_copy_from_user_iovec(char *vaddr,
                 bytes -= len;
                 vaddr += len;
                 if (unlikely(left)) {
-                        /*
-                         * Zero the rest of the target like __copy_from_user().
-                         */
-                        memset(vaddr, 0, bytes);
                         total -= left;
                         break;
                 }
@@ -1420,11 +1416,13 @@ static inline void ntfs_set_next_iovec(const struct iovec **iovp,
  * pages (out to offset + bytes), to emulate ntfs_copy_from_user()'s
  * single-segment behaviour.
  *
- * We call the same helper (__ntfs_copy_from_user_iovec()) both when atomic and
- * when not atomic.  This is ok because __ntfs_copy_from_user_iovec() calls
- * __copy_from_user_inatomic() and it is ok to call this when non-atomic.  In
- * fact, the only difference between __copy_from_user_inatomic() and
- * __copy_from_user() is that the latter calls might_sleep().  And on many
+ * We call the same helper (__ntfs_copy_from_user_iovec_inatomic()) both
+ * when atomic and when not atomic.  This is ok because
+ * __ntfs_copy_from_user_iovec_inatomic() calls __copy_from_user_inatomic()
+ * and it is ok to call this when non-atomic.
+ * Infact, the only difference between __copy_from_user_inatomic() and
+ * __copy_from_user() is that the latter calls might_sleep() and the former
+ * should not zero the tail of the buffer on error.  And on many
  * architectures __copy_from_user_inatomic() is just defined to
  * __copy_from_user() so it makes no difference at all on those architectures.
  */
@@ -1441,14 +1439,18 @@ static inline size_t ntfs_copy_from_user_iovec(struct page **pages,
                 if (len > bytes)
                         len = bytes;
                 kaddr = kmap_atomic(*pages, KM_USER0);
-                copied = __ntfs_copy_from_user_iovec(kaddr + ofs,
+                copied = __ntfs_copy_from_user_iovec_inatomic(kaddr + ofs,
                                 *iov, *iov_ofs, len);
                 kunmap_atomic(kaddr, KM_USER0);
                 if (unlikely(copied != len)) {
                         /* Do it the slow way. */
                         kaddr = kmap(*pages);
-                        copied = __ntfs_copy_from_user_iovec(kaddr + ofs,
+                        copied = __ntfs_copy_from_user_iovec_inatomic(kaddr + ofs,
                                         *iov, *iov_ofs, len);
+                        /*
+                         * Zero the rest of the target like __copy_from_user().
+                         */
+                        memset(kaddr + ofs + copied, 0, len - copied);
                         kunmap(*pages);
                         if (unlikely(copied != len))
                                 goto err_out;
diff --git a/include/asm-i386/uaccess.h b/include/asm-i386/uaccess.h
index 8462f8e0e658..d0d253277be5 100644
--- a/include/asm-i386/uaccess.h
+++ b/include/asm-i386/uaccess.h
@@ -458,6 +458,12 @@ __copy_to_user(void __user *to, const void *from, unsigned long n)
  *
  * If some data could not be copied, this function will pad the copied
  * data to the requested size using zero bytes.
+ *
+ * An alternate version - __copy_from_user_inatomic() - may be called from
+ * atomic context and will fail rather than sleep.  In this case the
+ * uncopied bytes will *NOT* be padded with zeros.  See fs/filemap.h
+ * for explanation of why this is needed.
+ * FIXME this isn't implimented yet EMXIF
  */
 static __always_inline unsigned long
 __copy_from_user_inatomic(void *to, const void __user *from, unsigned long n)
diff --git a/mm/filemap.c b/mm/filemap.c
index 807a463fd5ed..1ed4be2a7654 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1892,7 +1892,7 @@ int remove_suid(struct dentry *dentry)
 EXPORT_SYMBOL(remove_suid);
 
 size_t
-__filemap_copy_from_user_iovec(char *vaddr, 
+__filemap_copy_from_user_iovec_inatomic(char *vaddr,
                         const struct iovec *iov, size_t base, size_t bytes)
 {
         size_t copied = 0, left = 0;
@@ -1908,12 +1908,8 @@ __filemap_copy_from_user_iovec(char *vaddr,
                 vaddr += copy;
                 iov++;
 
-                if (unlikely(left)) {
-                        /* zero the rest of the target like __copy_from_user */
-                        if (bytes)
-                                memset(vaddr, 0, bytes);
+                if (unlikely(left))
                         break;
-                }
         }
         return copied - left;
 }
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;