linux-kernel - Re: [syzbot] BUG: bad usercopy in io_openat2

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Message-ID: <9552a45f-6a26-e7fa-aa63-3c74a7d17261@gmail.com>
Date:   Sun, 12 Feb 2023 15:47:13 +0000
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Kees Cook <kees@...nel.org>,
        syzbot <syzbot+cdd9922704fc75e03ffc@...kaller.appspotmail.com>,
        akpm@...ux-foundation.org, keescook@...omium.org,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, syzkaller-bugs@...glegroups.com,
        io-uring@...r.kernel.org
Subject: Re: [syzbot] BUG: bad usercopy in io_openat2_prep

On 2/11/23 16:36, Kees Cook wrote:
> On February 11, 2023 8:08:52 AM PST, syzbot <syzbot+cdd9922704fc75e03ffc@...kaller.appspotmail.com> wrote:
>> Hello,
>>
>> syzbot found the following issue on:
>>
>> HEAD commit:    ca72d58361ee Merge branch 'for-next/core' into for-kernelci
>> git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
>> console output: https://syzkaller.appspot.com/x/log.txt?x=14a882f3480000
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=f3e78232c1ed2b43
>> dashboard link: https://syzkaller.appspot.com/bug?extid=cdd9922704fc75e03ffc
>> compiler:       Debian clang version 15.0.7, GNU ld (GNU Binutils for Debian) 2.35.2
>> userspace arch: arm64
>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1203777b480000
>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=124c1ea3480000

I couldn't reproduce it, let's try latest io_uring first

#syz test: https://git.kernel.dk/linux.git for-6.3/io_uring


>> Downloadable assets:
>> disk image: https://storage.googleapis.com/syzbot-assets/e2c91688b4cd/disk-ca72d583.raw.xz
>> vmlinux: https://storage.googleapis.com/syzbot-assets/af105438bee6/vmlinux-ca72d583.xz
>> kernel image: https://storage.googleapis.com/syzbot-assets/4a28ec4f8f7e/Image-ca72d583.gz.xz
>>
>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>> Reported-by: syzbot+cdd9922704fc75e03ffc@...kaller.appspotmail.com
>>
>> usercopy: Kernel memory overwrite attempt detected to SLUB object 'pid' (offset 24, size 24)!
> 
> This looks like some serious memory corruption. The pid slab is 24 bytes in size, but struct io_open is larger... Possible UAF after the memory being reallocated to a new slab??
> 
> -Kees
> 
>> [...]
>> Call trace:
>> usercopy_abort+0x90/0x94
>> __check_heap_object+0xa8/0x100
>> __check_object_size+0x208/0x6b8
>> io_openat2_prep+0xcc/0x2b8
>> io_submit_sqes+0x338/0xbb8
>> __arm64_sys_io_uring_enter+0x168/0x1308
>> invoke_syscall+0x64/0x178
>> el0_svc_common+0xbc/0x180
>> do_el0_svc+0x48/0x110
>> el0_svc+0x58/0x14c
>> el0t_64_sync_handler+0x84/0xf0
>> el0t_64_sync+0x190/0x194
> 
> 
> 

-- 
Pavel Begunkov