[PATCH] Wrong assumption in set_bh_page()

[Mark Hemment]

  set_bh_page() assumes page_address() will always return NULL for a
highmem page.  This assumption is wrong - the highmem page could be
kmap()ped.

  Luckily, no code I've looked at assumes that b_data contains a _pure_
offset for a highmem page, but this is a bug waiting to happen.

  Patch is against 2.4.21-rc1.

Mark


diff -urN linux-2.4.21-rc1/fs/buffer.c linux-2.4.21-rc1-bh/fs/buffer.c
--- linux-2.4.21-rc1/fs/buffer.c	2003-08-17 15:55:40.000000000 +0100
+++ linux-2.4.21-rc1-bh/fs/buffer.c	2003-08-17 18:15:13.000000000 +0100
@@ -1231,10 +1231,11 @@
 	if (offset >= PAGE_SIZE)
 		BUG();

-	/*
-	 * page_address will return NULL anyways for highmem pages
-	 */
-	bh->b_data = page_address(page) + offset;
+	if (PageHighMem(page)) {
+		bh->b_data = (char *)offset;
+	} else {
+		bh->b_data = page_address(page) + offset;
+	}
 	bh->b_page = page;
 }
 EXPORT_SYMBOL(set_bh_page);



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