lkml.org 
[lkml]   [2011]   [Mar]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Date
SubjectRe: [PATCH] [RFC] Make it easier to harden /proc/
Alexey Dobriyan <adobriyan@gmail.com> writes:

> On Wed, Mar 16, 2011 at 09:08:16PM +0100, Richard Weinberger wrote:
>> Kees,
>>
>> Am Mittwoch 16 März 2011, 20:55:49 schrieb Kees Cook:
>> > Hi Richard,
>> >
>> > On Wed, Mar 16, 2011 at 08:31:47PM +0100, Richard Weinberger wrote:
>> > > When containers like LXC are used a unprivileged and jailed
>> > > root user can still write to critical files in /proc/.
>> > > E.g: /proc/sys/kernel/{sysrq, panic, panic_on_oops, ... }
>> > >
>> > > This new restricted attribute makes it possible to protect such
>> > > files. When restricted is set to true root needs CAP_SYS_ADMIN
>> > > to into the file.
>> >
>> > I was thinking about this too. I'd prefer more fine-grained control
>> > in this area, since some sysctl entries aren't strictly controlled by
>> > CAP_SYS_ADMIN (e.g. mmap_min_addr is already checking CAP_SYS_RAWIO).
>> >
>> > How about this instead?
>>
>> Good Idea.
>> May we should also consider a per-directory restriction.
>> Every file in /proc/sys/{kernel/, vm/, fs/, dev/} needs a protection.
>> It would be much easier to set the protection on the parent directory
>> instead of protecting file by file...
>
> Of course, not.
>
> You should _enable_ them one by one, not the other way around.
>
> "default deny"

Right.

Since the primary problem here is containers we can use the
user_namespace to add the default deny policy.

Something like the trivial patch below should make /proc/sys safe,
and the technique applies in general.

Richard is that a good enough example to get you started?

Eric

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 0f1bd83..a172a9d 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1674,10 +1674,12 @@ void register_sysctl_root(struct ctl_table_root *root)

static int test_perm(int mode, int op)
{
- if (!current_euid())
- mode >>= 6;
- else if (in_egroup_p(0))
- mode >>= 3;
+ if (current_user_ns() == &init_user_ns) {
+ if (!current_euid())
+ mode >>= 6;
+ else if (in_egroup_p(0))
+ mode >>= 3;
+ }
if ((op & ~mode & (MAY_READ|MAY_WRITE|MAY_EXEC)) == 0)
return 0;
return -EACCES;

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2011-03-17 17:53    [W:0.296 / U:0.032 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site