From: "Isaac J. Manjarres" isaacm@codeaurora.org Subject: 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... 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 ---

mm/usercopy.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/usercopy.c~mm-usercopy-use-memory-range-to-be-accessed-for-wraparound-check +++ a/mm/usercopy.c @@ -147,7 +147,7 @@ static inline void check_bogus_address(c 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. */ _