From: Prasad Sodagudi psodagud@codeaurora.org

commit 951531691c4bcaa59f56a316e018bc2ff1ddf855 upstream.

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 Signed-off-by: Linus Torvalds torvalds@linux-foundation.org [kees: backport to v4.9] Signed-off-by: Kees Cook keescook@chromium.org --- mm/usercopy.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/usercopy.c b/mm/usercopy.c index 3c8da0af9695..7683c22551ff 100644 --- a/mm/usercopy.c +++ b/mm/usercopy.c @@ -124,7 +124,7 @@ static inline const char *check_kernel_text_object(const void *ptr, static inline const char *check_bogus_address(const void *ptr, unsigned long n) { /* Reject if object wraps past end of memory. */ - if ((unsigned long)ptr + n < (unsigned long)ptr) + if ((unsigned long)ptr + (n - 1) < (unsigned long)ptr) return "<wrapped address>";

/* Reject if NULL or ZERO-allocation. */