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Date: Fri, 14 Oct 2016 09:38:46 -0400 From: "J. Bruce Fields" <bfields@...ldses.org> To: Jeff Layton <jlayton@...hat.com> Cc: Jiri Slaby <jslaby@...e.cz>, viro@...iv.linux.org.uk, linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org Subject: Re: [PATCH] fs: fcntl, avoid undefined behaviour On Fri, Oct 14, 2016 at 07:48:15AM -0400, Jeff Layton wrote: > On Fri, 2016-10-14 at 11:23 +0200, 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; > > Might it be better to change f_setown to return int there, so you can > return -EINVAL in that case? The other caller (sock_ioctl) can also > handle an int return there too... That might also be worth a note in the RETURN VALUE section of fcntl(2), which goes into surprising detail about the EINVAL cases for different commands. --b.
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