From: "Isaac J. Manjarres" <isaacm@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx Fixes: f5509cc18daa ("mm: Hardened usercopy") Signed-off-by: Prasad Sodagudi <psodagud@xxxxxxxxxxxxxx> Signed-off-by: Isaac J. Manjarres <isaacm@xxxxxxxxxxxxxx> Co-developed-by: Prasad Sodagudi <psodagud@xxxxxxxxxxxxxx> Reviewed-by: William Kucharski <william.kucharski@xxxxxxxxxx> Acked-by: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> Cc: Trilok Soni <tsoni@xxxxxxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- 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. */ _
