linux-kernel - Re: [syzbot] [hardening?] [mm?] BUG: bad usercopy in fpa

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Message-ID: <dcf54740-7cc3-4017-ad1b-8626a22fc15e@I-love.SAKURA.ne.jp>
Date: Tue, 5 Mar 2024 20:27:07 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: Linux ARM <linux-arm-kernel@...ts.infradead.org>
Cc: syzbot <syzbot+cb76c2983557a07cdb14@...kaller.appspotmail.com>,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [hardening?] [mm?] BUG: bad usercopy in fpa_set

Hello.

syzbot is reporting kernel memory overwrite attempt at fpa_set().
I guessed that the amount to copy from/to should be sizeof(union fp_state)
than sizeof(struct user_fp), for arch_ptrace(PTRACE_[SG]ETFPREGS) for arm
is using offset == 0 and size == sizeof(union fp_state). But my guess did not
solve the issue ( https://syzkaller.appspot.com/x/patch.diff?x=11e46dbc180000 ).

On 2023/05/05 21:53, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    457391b03803 Linux 6.3
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=105b8bb0280000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=385e197a58ca4afe
> dashboard link: https://syzkaller.appspot.com/bug?extid=cb76c2983557a07cdb14
> compiler:       arm-linux-gnueabi-gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> userspace arch: arm

#syz set subsystems: arm