Avoid pgoff overflow in remap_file_pages

LarryWoodman · torvalds · commit 5ec1055aa563 · 2010-09-25T09:34:58.000-07:00
Thomas Pollet noticed that the remap_file_pages() system call in
fremap.c has a potential overflow in the first part of the if statement
below, which could cause it to process bogus input parameters.
Specifically the pgoff + size parameters could be wrap thereby
preventing the system call from failing when it should.

Reported-by: Thomas Pollet &lt;thomas.pollet@gmail.com&gt;
Signed-off-by: Larry Woodman &lt;lwoodman@redhat.com&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
diff --git a/mm/fremap.c b/mm/fremap.c
@@ -141,6 +141,10 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
 	if (start + size <= start)
 		return err;
 
+	/* Does pgoff wrap? */
+	if (pgoff + (size >> PAGE_SHIFT) < pgoff)
+		return err;
+
 	/* Can we represent this offset inside this architecture's pte's? */
 #if PTE_FILE_MAX_BITS < BITS_PER_LONG
 	if (pgoff + (size >> PAGE_SHIFT) >= (1UL << PTE_FILE_MAX_BITS))
