linux-kernel - Re: [PATCH 03/11] security: commoncap: fix -Wstringop-overread warning

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Message-ID: <20210322163131.yaovowes2raydgyg@wittgenstein>
Date:   Mon, 22 Mar 2021 17:31:31 +0100
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Martin Sebor <msebor@....gnu.org>,
        Serge Hallyn <serge@...lyn.com>,
        James Morris <jmorris@...ei.org>,
        Arnd Bergmann <arnd@...db.de>, x86@...nel.org,
        Ning Sun <ning.sun@...el.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        Simon Kelley <simon@...kelleys.org.uk>,
        James Smart <james.smart@...adcom.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        Anders Larsen <al@...rsen.net>, Tejun Heo <tj@...nel.org>,
        Imre Deak <imre.deak@...el.com>,
        linux-arm-kernel@...ts.infradead.org,
        tboot-devel@...ts.sourceforge.net, intel-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, ath11k@...ts.infradead.org,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-scsi@...r.kernel.org, cgroups@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Tycho Andersen <tycho@...ho.pizza>
Subject: Re: [PATCH 03/11] security: commoncap: fix -Wstringop-overread
 warning

On Mon, Mar 22, 2021 at 05:02:41PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> gcc-11 introdces a harmless warning for cap_inode_getsecurity:
> 
> security/commoncap.c: In function ‘cap_inode_getsecurity’:
> security/commoncap.c:440:33: error: ‘memcpy’ reading 16 bytes from a region of size 0 [-Werror=stringop-overread]
>   440 |                                 memcpy(&nscap->data, &cap->data, sizeof(__le32) * 2 * VFS_CAP_U32);
>       |                                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> The problem here is that tmpbuf is initialized to NULL, so gcc assumes
> it is not accessible unless it gets set by vfs_getxattr_alloc().  This is
> a legitimate warning as far as I can tell, but the code is correct since
> it correctly handles the error when that function fails.
> 
> Add a separate NULL check to tell gcc about it as well.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---

Seems reasonable,
Acked-by: Christian Brauner <christian.brauner@...ntu.com>