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Message-ID: <bd11473cd4e2a92c4ce2a32d370800522862ad4b.camel@redhat.com>
Date: Thu, 20 Oct 2022 10:58:50 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Kees Cook <keescook@...omium.org>, Jakub Kicinski <kuba@...nel.org>
Cc: "David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jens Axboe <axboe@...nel.dk>,
Pavel Begunkov <asml.silence@...il.com>,
David Ahern <dsahern@...nel.org>,
Dylan Yudaken <dylany@...com>,
Yajun Deng <yajun.deng@...ux.dev>,
Petr Machata <petrm@...dia.com>,
Hangbin Liu <liuhangbin@...il.com>,
Leon Romanovsky <leon@...nel.org>,
syzbot <syzkaller@...glegroups.com>,
Willem de Bruijn <willemb@...gle.com>,
Pablo Neira Ayuso <pablo@...filter.org>,
netdev@...r.kernel.org, Nathan Chancellor <nathan@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Tom Rix <trix@...hat.com>,
"D. Wythe" <alibuda@...ux.alibaba.com>,
Jeremy Kerr <jk@...econstruct.com.au>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Menglong Dong <imagedong@...cent.com>,
Kuniyuki Iwashima <kuniyu@...zon.com>,
Congyu Liu <liu3101@...due.edu>,
Wolfram Sang <wsa+renesas@...g-engineering.com>,
Ziyang Xuan <william.xuanziyang@...wei.com>,
linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] net: dev: Convert sa_data to flexible array in
struct sockaddr
Hello,
On Tue, 2022-10-18 at 02:56 -0700, Kees Cook wrote:
> One of the worst offenders of "fake flexible arrays" is struct sockaddr,
> as it is the classic example of why GCC and Clang have been traditionally
> forced to treat all trailing arrays as fake flexible arrays: in the
> distant misty past, sa_data became too small, and code started just
> treating it as a flexible array, even though it was fixed-size. The
> special case by the compiler is specifically that sizeof(sa->sa_data)
> and FORTIFY_SOURCE (which uses __builtin_object_size(sa->sa_data, 1))
> do not agree (14 and -1 respectively), which makes FORTIFY_SOURCE treat
> it as a flexible array.
>
> However, the coming -fstrict-flex-arrays compiler flag will remove
> these special cases so that FORTIFY_SOURCE can gain coverage over all
> the trailing arrays in the kernel that are _not_ supposed to be treated
> as a flexible array. To deal with this change, convert sa_data to a true
> flexible array. To keep the structure size the same, move sa_data into
> a union with a newly introduced sa_data_min with the original size. The
> result is that FORTIFY_SOURCE can continue to have no idea how large
> sa_data may actually be, but anything using sizeof(sa->sa_data) must
> switch to sizeof(sa->sa_data_min).
>
> Cc: Jakub Kicinski <kuba@...nel.org>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Eric Dumazet <edumazet@...gle.com>
> Cc: Paolo Abeni <pabeni@...hat.com>
> Cc: Jens Axboe <axboe@...nel.dk>
> Cc: Pavel Begunkov <asml.silence@...il.com>
> Cc: David Ahern <dsahern@...nel.org>
> Cc: Dylan Yudaken <dylany@...com>
> Cc: Yajun Deng <yajun.deng@...ux.dev>
> Cc: Petr Machata <petrm@...dia.com>
> Cc: Hangbin Liu <liuhangbin@...il.com>
> Cc: Leon Romanovsky <leon@...nel.org>
> Cc: syzbot <syzkaller@...glegroups.com>
> Cc: Willem de Bruijn <willemb@...gle.com>
> Cc: Pablo Neira Ayuso <pablo@...filter.org>
> Cc: netdev@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
> include/linux/socket.h | 5 ++++-
> net/core/dev.c | 2 +-
> net/core/dev_ioctl.c | 2 +-
> net/packet/af_packet.c | 10 +++++-----
> 4 files changed, 11 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/socket.h b/include/linux/socket.h
> index de3701a2a212..13c3a237b9c9 100644
> --- a/include/linux/socket.h
> +++ b/include/linux/socket.h
> @@ -33,7 +33,10 @@ typedef __kernel_sa_family_t sa_family_t;
>
> struct sockaddr {
> sa_family_t sa_family; /* address family, AF_xxx */
> - char sa_data[14]; /* 14 bytes of protocol address */
> + union {
> + char sa_data_min[14]; /* Minimum 14 bytes of protocol address */
> + DECLARE_FLEX_ARRAY(char, sa_data);
Any special reason to avoid preserving the old name for the array and
e.g. using sa_data_flex for the new field, so we don't have to touch
the sockaddr users?
Thanks!
Paolo
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