Re: [PATCH v3 3/3] treewide: use get_random_u32_inclusive() when possible

Kees Cook
2022-11-17T21:58:16Z

On Thu, Nov 17, 2022 at 09:29:06PM +0100, Jason A. Donenfeld wrote:
> These cases were done with this Coccinelle:
>
> @@
> expression H;
> expression L;
> @@
> - (get_random_u32_below(H) + L)
> + get_random_u32_inclusive(L, H + L - 1)
>
> @@
> expression H;
> expression L;
> expression E;
> @@
> get_random_u32_inclusive(L,
> H
> - + E
> - - E
> )
>
> @@
> expression H;
> expression L;
> expression E;
> @@
> get_random_u32_inclusive(L,
> H
> - - E
> - + E
> )
>
> @@
> expression H;
> expression L;
> expression E;
> expression F;
> @@
> get_random_u32_inclusive(L,
> H
> - - E
> + F
> - + E
> )
>
> @@
> expression H;
> expression L;
> expression E;
> expression F;
> @@
> get_random_u32_inclusive(L,
> H
> - + E
> + F
> - - E
> )
>
> And then subsequently cleaned up by hand, with several automatic cases
> rejected if it didn't make sense contextually.
>
> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> # for infiniband
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
> ---
> arch/x86/kernel/module.c | 2 +-
> crypto/rsa-pkcs1pad.c | 2 +-
> crypto/testmgr.c | 10 ++++----
> drivers/bus/mhi/host/internal.h | 2 +-
> drivers/dma-buf/st-dma-fence-chain.c | 2 +-
> drivers/infiniband/core/cma.c | 2 +-
> drivers/infiniband/hw/hns/hns_roce_ah.c | 5 ++--
> drivers/mtd/nand/raw/nandsim.c | 2 +-
> drivers/net/wireguard/selftest/allowedips.c | 8 +++---
> .../broadcom/brcm80211/brcmfmac/p2p.c | 2 +-
> .../net/wireless/intel/iwlwifi/mvm/mac-ctxt.c | 2 +-
> fs/f2fs/segment.c | 6 ++---
> kernel/kcsan/selftest.c | 2 +-
> lib/test_hexdump.c | 10 ++++----
> lib/test_printf.c | 2 +-
> lib/test_vmalloc.c | 6 ++---
> mm/kasan/kasan_test.c | 6 ++---
> mm/kfence/kfence_test.c | 2 +-
> mm/swapfile.c | 5 ++--
> net/bluetooth/mgmt.c | 5 ++--
> net/core/pktgen.c | 25 ++++++++-----------
> net/ipv4/tcp_input.c | 2 +-
> net/ipv6/addrconf.c | 6 ++---
> net/netfilter/nf_nat_helper.c | 2 +-
> net/xfrm/xfrm_state.c | 2 +-
> 25 files changed, 56 insertions(+), 64 deletions(-)

Even the diffstat agrees this is a nice clean-up. :)

Reviewed-by: Kees Cook <keescook@chromium.org>

The only comment I have is that maybe these cases can just be left as-is
with _below()?

> - size_t len = get_random_u32_below(rs) + gs;
> + size_t len = get_random_u32_inclusive(gs, rs + gs - 1);

It seems like writing it in the form of base plus [0, limit) is clearer?

size_t len = gs + get_random_u32_below(rs);

But there is only a handful, so *shrug*

All the others are much cleaner rewritten as _inclusive().

--
Kees Cook