mm/usercopy: use memory range to be accessed for wraparound check

Currently, when checking to see if accessing n bytes starting at address
"ptr" will cause a wraparound in the memory addresses, the check in
check_bogus_address() adds an extra byte, which is incorrect, as the
range of addresses that will be accessed is [ptr, ptr + (n - 1)].

This can lead to incorrectly detecting a wraparound in the memory
address, when trying to read 4 KB from memory that is mapped to the the
last possible page in the virtual address space, when in fact, accessing
that range of memory would not cause a wraparound to occur.

Use the memory range that will actually be accessed when considering if
accessing a certain amount of bytes will cause the memory address to
wrap around.

Link: http://lkml.kernel.org/r/1564509253-23287-1-git-send-email-isaacm@codeaurora.org
Fixes: f5509cc18daa ("mm: Hardened usercopy")
Signed-off-by: Prasad Sodagudi <psodagud@codeaurora.org>
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>
Co-developed-by: Prasad Sodagudi <psodagud@codeaurora.org>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Trilok Soni <tsoni@codeaurora.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/usercopy.c b/mm/usercopy.c
index 2a09796..98e9248 100644 (file)
--- a/mm/usercopy.c
+++ b/mm/usercopy.c
@@ -147,7 +147,7 @@ static inline void check_bogus_address(const unsigned long ptr, unsigned long n,
                                       bool to_user)
 {
        /* Reject if object wraps past end of memory. */
-       if (ptr + n < ptr)
+       if (ptr + (n - 1) < ptr)
                usercopy_abort("wrapped address", NULL, to_user, 0, ptr + n);
 
        /* Reject if NULL or ZERO-allocation. */