linux-kernel - Re: WARNING in ex_handler

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:   Wed, 23 Sep 2020 05:26:05 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Andy Lutomirski <luto@...nel.org>,
        syzbot <syzbot+ea3a78a71705faf41d77@...kaller.appspotmail.com>,
        Aleksa Sarai <cyphar@...har.com>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        syzkaller-bugs@...glegroups.com,
        Thomas Gleixner <tglx@...utronix.de>, X86 ML <x86@...nel.org>
Subject: Re: WARNING in ex_handler_uaccess

On Mon, Sep 21, 2020 at 12:22:19PM +0200, Rasmus Villemoes wrote:

> So, not sure how the above got triggered, but I notice there might be an
> edge case in check_zeroed_user():
> 
> 	from -= align;
> 	size += align;
> 
> 	if (!user_read_access_begin(from, size))
> 		return -EFAULT;
> 
> 	unsafe_get_user(val, (unsigned long __user *) from, err_fault);
> 
> 
> Suppose size is (size_t)-3 and align is 3. What's the convention for
> access_ok(whatever, 0)? Is that equivalent to access_ok(whatever, 1), or
> is it always true (or $ARCH-dependent)?

It's usually true...

> But, AFAICT, no current caller of check_zeroed_user can end up passing
> in a size that can overflow to 0. E.g. for the case at hand, size cannot
> be more than SIZE_MAX-24.

Might be worth slapping if (unlikely(!size)) return -EFAULT; // overflow
just before user_read_access_begin() to be sure...