Re: [PATCH] fs: fcntl, avoid undefined behaviour

Jiri Slaby
2017-06-13T09:29:29Z

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@suse.cz>
>> Cc: Jeff Layton <jlayton@poochiereds.net>
>> Cc: "J. Bruce Fields" <bfields@fieldses.org>
>> Cc: Alexander Viro <viro@zeniv.linux.org.uk>
>> Cc: linux-fsdevel@vger.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