On Tue, Nov 13, 2018 at 6:51 PM, Isaac J. Manjarres isaacm@codeaurora.org wrote:
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.
I'm kind of surprised anything is using the -4K memory range -- this is ERR_PTR() area and I'd expect there to be an explicit unallocated memory hole here.
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.
Change-Id: I2563a5988e41122727ede17180f365e999b953e6 Fixes: f5509cc18daa ("mm: Hardened usercopy") Co-Developed-by: Prasad Sodagudi psodagud@codeaurora.org Signed-off-by: Prasad Sodagudi psodagud@codeaurora.org Signed-off-by: Isaac J. Manjarres isaacm@codeaurora.org Cc: stable@vger.kernel.org
Regardless, I'll take it in my tree if akpm doesn't grab it first. :)
Acked-by: Kees Cook keescook@chromium.org
-Kees
mm/usercopy.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/usercopy.c b/mm/usercopy.c index 852eb4e..0293645 100644 --- a/mm/usercopy.c +++ b/mm/usercopy.c @@ -151,7 +151,7 @@ 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. */-- The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project