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.
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 Reviewed-by: William Kucharski william.kucharski@oracle.com Acked-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 2a09796..98e92486 100644 --- 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. */
On Tue, Jul 30, 2019 at 10:54:13AM -0700, Isaac J. Manjarres 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.
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.
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 Reviewed-by: William Kucharski william.kucharski@oracle.com Acked-by: Kees Cook keescook@chromium.org
Ah, thanks for the reminder! (I got surprised by seeing my Ack in this email -- next time please use "v2" or "RESEND" to jog my memory.) This got lost last year; my bad.
Andrew, can you take this or should I send it directly to Linus?
-Kees
mm/usercopy.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/usercopy.c b/mm/usercopy.c index 2a09796..98e92486 100644 --- 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. */ -- The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project
linux-stable-mirror@lists.linaro.org
-
Isaac J. Manjarres -
Kees Cook