linux-kernel - check capabilities in open()

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Date:	Sat, 24 Jul 2010 20:07:01 +0400
From:	Vasiliy Kulikov <segooon@...il.com>
To:	kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: check capabilities in open()

Hi,

I've found that some drivers check process capabilities via capable() in
open(), not in ioctl()/write()/etc.

I cannot find answer in POSIX, but IMO process expects that file
descriptors of priviledged user and file descriptors of the same
file/device are the same in priviledge aspect. Driver should deny/allow
open() and deny/allow ioctl() based on user priviledges. The path how
the process gained this fd doesn't matter.

So I think these 2 examples should be equal:

1) root process opened the file and then dropped its priviledges

2) nonroot process opened the file

Currently gained fds are different in priviledge aspect.

If you think these are bugs, I can move capable() checking down to
ioctl()/write()/read()/etc.

This is the full list of such drivers:

drivers/staging/comedi/comedi_fops.c
drivers/oprofile/event_buffer.c
drivers/s390/char/vmcp.c
drivers/s390/char/zcore.c
drivers/net/ppp_generic.c
drivers/scsi/3w-sas.c
drivers/scsi/pmcraid.c
drivers/scsi/megaraid.c
drivers/scsi/megaraid/megaraid_sas.c
drivers/scsi/megaraid/megaraid_mm.c
drivers/char/mem.c
drivers/char/tty_io.c
drivers/char/agp/frontend.c
drivers/char/apm-emulation.c

This is coccinelle script to find that:

@ r1 @
identifier fops;
identifier openx;
@@

struct file_operations fops = {
...
.open       = openx,
...
};

@@
identifier r1.openx;
@@

openx(...)
{
...
*capable(...)
...
}
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