linux-kernel - Re: [PATCH] fs: fcntl, avoid undefined behaviour

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Message-ID: <53f29baf-4da1-f2db-aec4-32291dc8db7d@suse.cz>
Date:   Tue, 13 Jun 2017 11:29:23 +0200
From:   Jiri Slaby <jslaby@...e.cz>
To:     zhong jiang <zhongjiang@...wei.com>
Cc:     viro@...iv.linux.org.uk, linux-kernel@...r.kernel.org,
        Jeff Layton <jlayton@...chiereds.net>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        linux-fsdevel@...r.kernel.org, Xishi Qiu <qiuxishi@...wei.com>
Subject: Re: [PATCH] fs: fcntl, avoid undefined behaviour

On 06/12/2017, 07:03 AM, zhong jiang wrote:
> On 2016/10/14 17:23, Jiri Slaby wrote:
>> fcntl(0, F_SETOWN, 0x80000000) triggers:
>> UBSAN: Undefined behaviour in fs/fcntl.c:118:7
>> negation of -2147483648 cannot be represented in type 'int':
>> CPU: 1 PID: 18261 Comm: syz-executor Not tainted 4.8.1-0-syzkaller #1
>> ...
>> Call Trace:
>> ...
>>  [<ffffffffad8f0868>] ? f_setown+0x1d8/0x200
>>  [<ffffffffad8f19a9>] ? SyS_fcntl+0x999/0xf30
>>  [<ffffffffaed1fb00>] ? entry_SYSCALL_64_fastpath+0x23/0xc1
>>
>> Fix that by checking the arg parameter properly (against INT_MAX) and
>> return immediatelly in case it is wrong. No error is returned, the
>> same as in other cases.
>>
>> Signed-off-by: Jiri Slaby <jslaby@...e.cz>
>> Cc: Jeff Layton <jlayton@...chiereds.net>
>> Cc: "J. Bruce Fields" <bfields@...ldses.org>
>> Cc: Alexander Viro <viro@...iv.linux.org.uk>
>> Cc: linux-fsdevel@...r.kernel.org
>> ---
>>  fs/fcntl.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/fs/fcntl.c b/fs/fcntl.c
>> index 350a2c8cfd28..bfc3b040d956 100644
>> --- a/fs/fcntl.c
>> +++ b/fs/fcntl.c
>> @@ -112,6 +112,10 @@ void f_setown(struct file *filp, unsigned long arg, int force)
>>  	enum pid_type type;
>>  	struct pid *pid;
>>  	int who = arg;
>> +
>> +	if (arg > INT_MAX)
>> +		return;
>> +
>>  	type = PIDTYPE_PID;
>>  	if (who < 0
>>  		type = PIDTYPE_PGID;
> Hi, Jiri
> 
> I hit the same issue,  but I see the upstream is still not changed.  Had any problem?

Hi, it needed an update which I have just sent. So let's see if that
gets applied.

thanks,
-- 
js
suse labs