Avoid pgoff overflow in remap_file_pages

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 <thomas.pollet@gmail.com>
Signed-off-by: Larry Woodman <lwoodman@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/mm/fremap.c b/mm/fremap.c
index 7b7f852848de..ec520c7b28df 100644
--- 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))