In an effort to separate intentional arithmetic wrap-around from unexpected wrap-around, we need to refactor places that depend on this kind of math. One of the most common code patterns of this is: VAR + value < VAR Notably, this is considered "undefined behavior" for signed and pointer types, which the kernel works around by using the -fno-strict-overflow option in the build[1] (which used to just be -fwrapv). Regardless, we want to get the kernel source to the position where we can meaningfully instrument arithmetic wrap-around conditions and catch them when they are unexpected, regardless of whether they are signed[2], unsigned[3], or pointer[4] types. Refactor open-coded unsigned wrap-around addition test to use check_add_overflow(), retaining the result for later usage (which removes the redundant open-coded addition). This paves the way to enabling the unsigned wrap-around sanitizer[2] in the future. Link: https://git.kernel.org/linus/68df3755e383e6fecf2354a67b08f92f18536594 [1] Link: https://github.com/KSPP/linux/issues/26 [2] Link: https://github.com/KSPP/linux/issues/27 [3] Link: https://github.com/KSPP/linux/issues/344 [4] Cc: Santosh Shilimkar <santosh.shilimkar@xxxxxxxxxx> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx> Cc: Eric Dumazet <edumazet@xxxxxxxxxx> Cc: Jakub Kicinski <kuba@xxxxxxxxxx> Cc: Paolo Abeni <pabeni@xxxxxxxxxx> Cc: netdev@xxxxxxxxxxxxxxx Cc: linux-rdma@xxxxxxxxxxxxxxx Cc: rds-devel@xxxxxxxxxxxxxx Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> --- net/rds/info.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/net/rds/info.c b/net/rds/info.c index b6b46a8214a0..87b35d07ce04 100644 --- a/net/rds/info.c +++ b/net/rds/info.c @@ -163,6 +163,7 @@ int rds_info_getsockopt(struct socket *sock, int optname, char __user *optval, unsigned long nr_pages = 0; unsigned long start; rds_info_func func; + unsigned long sum; struct page **pages = NULL; int ret; int len; @@ -175,7 +176,8 @@ int rds_info_getsockopt(struct socket *sock, int optname, char __user *optval, /* check for all kinds of wrapping and the like */ start = (unsigned long)optval; - if (len < 0 || len > INT_MAX - PAGE_SIZE + 1 || start + len < start) { + if (len < 0 || len > INT_MAX - PAGE_SIZE + 1 || + check_add_overflow(start, len, &sum)) { ret = -EINVAL; goto out; } @@ -184,7 +186,7 @@ int rds_info_getsockopt(struct socket *sock, int optname, char __user *optval, if (len == 0) goto call_func; - nr_pages = (PAGE_ALIGN(start + len) - (start & PAGE_MASK)) + nr_pages = (PAGE_ALIGN(sum) - (start & PAGE_MASK)) >> PAGE_SHIFT; pages = kmalloc_array(nr_pages, sizeof(struct page *), GFP_KERNEL); -- 2.34.1
