linux-kernel - Re: [PATCH 2/9] libceph: avoid clang out-of-range warning

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Message-ID: <CAFhGd8rCzhqK18KLtLVLWyWHtQzJsHCkkkQQyLbmw83K6ExKkw@mail.gmail.com>
Date: Thu, 28 Mar 2024 15:53:35 -0700
From: Justin Stitt <justinstitt@...gle.com>
To: Arnd Bergmann <arnd@...nel.org>
Cc: linux-kernel@...r.kernel.org, Xiubo Li <xiubli@...hat.com>, 
	Ilya Dryomov <idryomov@...il.com>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Nathan Chancellor <nathan@...nel.org>, Arnd Bergmann <arnd@...db.de>, Jeff Layton <jlayton@...nel.org>, 
	Nick Desaulniers <ndesaulniers@...gle.com>, Bill Wendling <morbo@...gle.com>, 
	Milind Changire <mchangir@...hat.com>, Patrick Donnelly <pdonnell@...hat.com>, 
	Christian Brauner <brauner@...nel.org>, ceph-devel@...r.kernel.org, netdev@...r.kernel.org, 
	llvm@...ts.linux.dev
Subject: Re: [PATCH 2/9] libceph: avoid clang out-of-range warning

On Thu, Mar 28, 2024 at 7:31 AM Arnd Bergmann <arnd@...nel.org> wrote:
>
> From: Arnd Bergmann <arnd@...db.de>
>
> clang-14 points out that on 64-bit architectures, a u32
> is never larger than constant based on SIZE_MAX:
>
> net/ceph/osdmap.c:1425:10: error: result of comparison of constant 4611686018427387891 with expression of type 'u32' (aka 'unsigned int') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
>         if (len > (SIZE_MAX - sizeof(*pg)) / sizeof(u32))
>             ~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> net/ceph/osdmap.c:1608:10: error: result of comparison of constant 2305843009213693945 with expression of type 'u32' (aka 'unsigned int') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
>         if (len > (SIZE_MAX - sizeof(*pg)) / (2 * sizeof(u32)))
>             ~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> The code is correct anyway, so just shut up that warning.

OK.

>
> Fixes: 6f428df47dae ("libceph: pg_upmap[_items] infrastructure")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Reviewed-by: Justin Stitt <justinstitt@...gle.com>

> ---
>  fs/ceph/snap.c    | 2 +-
>  net/ceph/osdmap.c | 4 ++--
>  2 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
> index c65f2b202b2b..521507ea8260 100644
> --- a/fs/ceph/snap.c
> +++ b/fs/ceph/snap.c
> @@ -374,7 +374,7 @@ static int build_snap_context(struct ceph_mds_client *mdsc,
>
>         /* alloc new snap context */
>         err = -ENOMEM;
> -       if (num > (SIZE_MAX - sizeof(*snapc)) / sizeof(u64))
> +       if ((size_t)num > (SIZE_MAX - sizeof(*snapc)) / sizeof(u64))
>                 goto fail;
>         snapc = ceph_create_snap_context(num, GFP_NOFS);
>         if (!snapc)
> diff --git a/net/ceph/osdmap.c b/net/ceph/osdmap.c
> index 295098873861..8e7cb2fde6f1 100644
> --- a/net/ceph/osdmap.c
> +++ b/net/ceph/osdmap.c
> @@ -1438,7 +1438,7 @@ static struct ceph_pg_mapping *__decode_pg_temp(void **p, void *end,
>         ceph_decode_32_safe(p, end, len, e_inval);
>         if (len == 0 && incremental)
>                 return NULL;    /* new_pg_temp: [] to remove */
> -       if (len > (SIZE_MAX - sizeof(*pg)) / sizeof(u32))
> +       if ((size_t)len > (SIZE_MAX - sizeof(*pg)) / sizeof(u32))
>                 return ERR_PTR(-EINVAL);
>
>         ceph_decode_need(p, end, len * sizeof(u32), e_inval);
> @@ -1621,7 +1621,7 @@ static struct ceph_pg_mapping *__decode_pg_upmap_items(void **p, void *end,
>         u32 len, i;
>
>         ceph_decode_32_safe(p, end, len, e_inval);
> -       if (len > (SIZE_MAX - sizeof(*pg)) / (2 * sizeof(u32)))
> +       if ((size_t)len > (SIZE_MAX - sizeof(*pg)) / (2 * sizeof(u32)))
>                 return ERR_PTR(-EINVAL);
>
>         ceph_decode_need(p, end, 2 * len * sizeof(u32), e_inval);
> --
> 2.39.2
>