Re: [PATCH] mremap NULL pointer dereference fix

[Andrew Morton <akpm@osdl.org>]

Linus Torvalds <torvalds@osdl.org> wrote:
>
> Hmm.. Looking a bit more at it, does this alternate patch work? It's 
>  _slightly_ less ugly, and it also removes the nonsensical TLB invalidate 
>  instead of moving it around together with the comment that says that it 
>  shouldn't exist.
> 
>  The TLB is (properly) invalidated by "copy_one_pte()" if the mapping 
>  actually changes.
> 
>  Did I miss anything?

This saves a goto.   It works, but I wasn't able to trigger
the oops without it either.


diff -puN mm/mremap.c~mremap-oops-fix mm/mremap.c
--- 25/mm/mremap.c~mremap-oops-fix	2004-02-16 20:53:25.000000000 -0800
+++ 25-akpm/mm/mremap.c	2004-02-16 21:00:05.000000000 -0800
@@ -135,15 +135,17 @@ move_one_page(struct vm_area_struct *vma
 		dst = alloc_one_pte_map(mm, new_addr);
 		if (src == NULL)
 			src = get_one_pte_map_nested(mm, old_addr);
-		error = copy_one_pte(vma, old_addr, src, dst, &pte_chain);
-		pte_unmap_nested(src);
-		pte_unmap(dst);
-	} else
 		/*
-		 * Why do we need this flush ? If there is no pte for
-		 * old_addr, then there must not be a pte for it as well.
+		 * Since alloc_one_pte_map can drop and re-acquire
+		 * page_table_lock, we should re-check the src entry...
 		 */
-		flush_tlb_page(vma, old_addr);
+		if (src) {
+			error = copy_one_pte(vma, old_addr, src,
+						dst, &pte_chain);
+			pte_unmap_nested(src);
+		}
+		pte_unmap(dst);
+	}
 	spin_unlock(&mm->page_table_lock);
 	pte_chain_free(pte_chain);
 out:

_

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