Dear Linus, Alan, Ted, Andrew, all:
(i) Andrew - why don't you add yourself to the CREDITS file?
(then I'll find your email address at the first instead of the second attempt)
(ii) Yesterday I complained about the fact that pressing SAK twice
crashes the kernel (because the close from the first time will set
tty->driver_data = 0;
and then on the next press kbd has tty==0 and do_SAK() kills the system).
There is more bad stuff in this 2.4.3 patch:
-void do_SAK( struct tty_struct *tty)
+static void __do_SAK(void *arg)
{
#ifdef TTY_SOFT_SAK
tty_hangup(tty);
#else
+ struct tty_struct *tty = arg;
Clearly, if TTY_SOFT_SAK is defined this will not compile
(or, worse, will pick up some global variable tty).
The patch below has yesterdays fix of do_SAK(), and fixes this
compilation problem. I invented a separate inline routine here -
I do not like very long stretches of code inside #ifdef.
More interestingly, it changes the operation of SAK in two ways:
(a) It does less, namely will not kill processes with uid 0.
Ted, any objections?
For example, when syslog has several output streams, and one is
to /dev/tty10, then a SAK typed at /dev/tty10 should not kill syslog,
that is bad for security.
(b) It does more, namely will for the purposes of SAK consider all
VTs equivalent, so that a SAK typed on /dev/tty1 also kills processes
that have an open file descriptor on /dev/tty2.
That is good for security, since many keyboard or console ioctls just
require an open fd for some VT, and this process on tty2 can for example
change the keymap on tty1.
One of the motivations of this patch was that SAK should be able
to kill a "while [ 1 ]; do chvt 21; done", that is the reason
for the keyboard.c fragment.
Ted, please complain if anything is wrong with the way
filp->private_data is used.
Andries
diff -u --recursive --new-file ../linux-2.4.6-pre8/linux/drivers/char/keyboard.c ./linux/drivers/char/keyboard.c
--- ../linux-2.4.6-pre8/linux/drivers/char/keyboard.c Mon Oct 16 21:58:51 2000
+++ ./linux/drivers/char/keyboard.c Mon Jul 2 13:28:09 2001
@@ -506,6 +506,8 @@
* them properly.
*/
+ if (!tty && ttytab && ttytab[0] && ttytab[0]->driver_data)
+ tty = ttytab[0];
do_SAK(tty);
reset_vc(fg_console);
#if 0
diff -u --recursive --new-file ../linux-2.4.6-pre8/linux/drivers/char/tty_io.c ./linux/drivers/char/tty_io.c
--- ../linux-2.4.6-pre8/linux/drivers/char/tty_io.c Sun Jul 1 15:19:26 2001
+++ ./linux/drivers/char/tty_io.c Mon Jul 2 13:27:19 2001
@@ -1818,20 +1818,29 @@
*
* Nasty bug: do_SAK is being called in interrupt context. This can
* deadlock. We punt it up to process context. AKPM - 16Mar2001
+ *
+ * Treat all VTs as a single tty for the purposes of SAK. A process with an
+ * open fd for one VT can do interesting things to all. aeb, 2001-07-02
*/
-static void __do_SAK(void *arg)
+#ifdef CONFIG_VT
+static inline int tty_is_vt(struct tty_struct *tty)
{
-#ifdef TTY_SOFT_SAK
- tty_hangup(tty);
+ return tty ? (tty->driver.type == TTY_DRIVER_TYPE_CONSOLE) : 0;
+}
#else
- struct tty_struct *tty = arg;
+static inline int tty_is_vt(struct tty_struct *tty)
+{
+ return 0;
+}
+#endif
+
+static inline void tty_hard_SAK(struct tty_struct *tty)
+{
struct task_struct *p;
int session;
- int i;
- struct file *filp;
-
- if (!tty)
- return;
+ int i;
+ struct file *filp;
+
session = tty->session;
if (tty->ldisc.flush_buffer)
tty->ldisc.flush_buffer(tty);
@@ -1839,7 +1848,12 @@
tty->driver.flush_buffer(tty);
read_lock(&tasklist_lock);
for_each_task(p) {
+ /* do not kill root processes */
+ if (p->uid == 0)
+ continue;
+ /* all VTs are considered a single tty here */
if ((p->tty == tty) ||
+ (tty_is_vt(tty) && tty_is_vt(p->tty)) ||
((session > 0) && (p->session == session))) {
send_sig(SIGKILL, p, 1);
continue;
@@ -1850,7 +1864,9 @@
for (i=0; i < p->files->max_fds; i++) {
filp = fcheck_files(p->files, i);
if (filp && (filp->f_op == &tty_fops) &&
- (filp->private_data == tty)) {
+ (filp->private_data == tty ||
+ (tty_is_vt(tty) &&
+ tty_is_vt(filp->private_data)))) {
send_sig(SIGKILL, p, 1);
break;
}
@@ -1860,6 +1876,17 @@
task_unlock(p);
}
read_unlock(&tasklist_lock);
+}
+
+static void __do_SAK(void *arg)
+{
+ struct tty_struct *tty = arg;
+ if (!tty) /* impossible */
+ return;
+#ifdef TTY_SOFT_SAK
+ tty_hangup(tty);
+#else
+ tty_hard_SAK(tty);
#endif
}
@@ -1872,6 +1899,8 @@
*/
void do_SAK(struct tty_struct *tty)
{
+ if (!tty)
+ return;
PREPARE_TQUEUE(&tty->SAK_tq, __do_SAK, tty);
schedule_task(&tty->SAK_tq);
}
> (a) It does less, namely will not kill processes with uid 0.
> Ted, any objections?
That breaks the security guarantee. Suppose I use a setuid app to confuse
you into doing something ?
>> (a) It does less, namely will not kill processes with uid 0.
>> Ted, any objections?
Alan:
> That breaks the security guarantee. Suppose I use a setuid app to confuse
> you into doing something ?
You confuse me? Unlikely :-)
Indeed, discussion is possible. I think my version is more secure
and more useful, but if you disagree, delete the lines
/* do not kill root processes */
if (p->uid == 0)
continue;
Andries
>> (a) It does less, namely will not kill processes with uid 0.
>> Ted, any objections?
Alan:
> That breaks the security guarantee. Suppose I use a setuid app to confuse
> you into doing something ?
On second thoughts I agree. Here is the patch without test for p->uid.
Andries
diff -u --recursive --new-file ../linux-2.4.6-pre8/linux/drivers/char/keyboard.c ./linux/drivers/char/keyboard.c
--- ../linux-2.4.6-pre8/linux/drivers/char/keyboard.c Mon Oct 16 21:58:51 2000
+++ ./linux/drivers/char/keyboard.c Mon Jul 2 13:28:09 2001
@@ -506,6 +506,8 @@
* them properly.
*/
+ if (!tty && ttytab && ttytab[0] && ttytab[0]->driver_data)
+ tty = ttytab[0];
do_SAK(tty);
reset_vc(fg_console);
#if 0
diff -u --recursive --new-file ../linux-2.4.6-pre8/linux/drivers/char/tty_io.c ./linux/drivers/char/tty_io.c
--- ../linux-2.4.6-pre8/linux/drivers/char/tty_io.c Sun Jul 1 15:19:26 2001
+++ ./linux/drivers/char/tty_io.c Mon Jul 2 14:53:52 2001
@@ -1818,20 +1818,29 @@
*
* Nasty bug: do_SAK is being called in interrupt context. This can
* deadlock. We punt it up to process context. AKPM - 16Mar2001
+ *
+ * Treat all VTs as a single tty for the purposes of SAK. A process with an
+ * open fd for one VT can do interesting things to all. aeb, 2001-07-02
*/
-static void __do_SAK(void *arg)
+#ifdef CONFIG_VT
+static inline int tty_is_vt(struct tty_struct *tty)
{
-#ifdef TTY_SOFT_SAK
- tty_hangup(tty);
+ return tty ? (tty->driver.type == TTY_DRIVER_TYPE_CONSOLE) : 0;
+}
#else
- struct tty_struct *tty = arg;
+static inline int tty_is_vt(struct tty_struct *tty)
+{
+ return 0;
+}
+#endif
+
+static inline void tty_hard_SAK(struct tty_struct *tty)
+{
struct task_struct *p;
int session;
- int i;
- struct file *filp;
-
- if (!tty)
- return;
+ int i;
+ struct file *filp;
+
session = tty->session;
if (tty->ldisc.flush_buffer)
tty->ldisc.flush_buffer(tty);
@@ -1839,7 +1848,9 @@
tty->driver.flush_buffer(tty);
read_lock(&tasklist_lock);
for_each_task(p) {
+ /* all VTs are considered a single tty here */
if ((p->tty == tty) ||
+ (tty_is_vt(tty) && tty_is_vt(p->tty)) ||
((session > 0) && (p->session == session))) {
send_sig(SIGKILL, p, 1);
continue;
@@ -1850,7 +1861,9 @@
for (i=0; i < p->files->max_fds; i++) {
filp = fcheck_files(p->files, i);
if (filp && (filp->f_op == &tty_fops) &&
- (filp->private_data == tty)) {
+ (filp->private_data == tty ||
+ (tty_is_vt(tty) &&
+ tty_is_vt(filp->private_data)))) {
send_sig(SIGKILL, p, 1);
break;
}
@@ -1860,6 +1873,17 @@
task_unlock(p);
}
read_unlock(&tasklist_lock);
+}
+
+static void __do_SAK(void *arg)
+{
+ struct tty_struct *tty = arg;
+ if (!tty) /* impossible */
+ return;
+#ifdef TTY_SOFT_SAK
+ tty_hangup(tty);
+#else
+ tty_hard_SAK(tty);
#endif
}
@@ -1872,6 +1896,8 @@
*/
void do_SAK(struct tty_struct *tty)
{
+ if (!tty)
+ return;
PREPARE_TQUEUE(&tty->SAK_tq, __do_SAK, tty);
schedule_task(&tty->SAK_tq);
}
On Mon, Jul 02, 2001 at 02:16:36PM +0200, [email protected] wrote:
> (a) It does less, namely will not kill processes with uid 0.
> Ted, any objections?
What if you have a process running wild as uid 0 (i.e. X server gone bad) that you need to die *right now*?
--
"Don't dwell on reality; it will only keep you from greatness."
-- Randall McBride, Jr.
**
Evil Genius
Bryon Roche, Kain <[email protected]>
-> From Alan Cox <[email protected]> :
> > (a) It does less, namely will not kill processes with uid 0.
> > Ted, any objections?
>
> That breaks the security guarantee. Suppose I use a setuid app to confuse
> you into doing something ?
a setuid app only changes euid, doesn't it?
On Monday 02 July 2001 15:10, Hua Zhong wrote:
> -> From Alan Cox <[email protected]> :
> > > (a) It does less, namely will not kill processes with uid 0.
> > > Ted, any objections?
> >
> > That breaks the security guarantee. Suppose I use a setuid app to confuse
> > you into doing something ?
>
> a setuid app only changes euid, doesn't it?
Yup. And you'd be amazed how many fun little user mode things were either
never tested with the suid bit or obstinately refuse to run for no good
reason. (Okay, I made something like a sudo script. It's in a directory
that non-root users can't access and I'm being as careful as I know how to
be, but I've got a cgi that needs root access to query/set system and network
configuration.)
Off the top of my head, fun things you can't do suid root:
The samba adduser command. (But I CAN edit the smb.passwd file directly,
which got me around this.)
su without password (understandable, implementation detail. It's always
suid, being run by somebody other than root is how it knows when it NEEDS to
ask for a password. But when I want to DROP root privelidges... Wound up
making "suid-to" to do it.)
ps (What the...? Worked in Red Hat 7, but not in suse 7.1. Huh? "suid-to
apache ps ax" works fine, though...)
dhcpcd (I patched it and yelled at the maintainer of this months ago, should
be fixed now. But a clear case of checking uid when he meant euid, which is
outright PERVASIVE...).
I keep bumping into more of these all the time. Often it's fun little
warnings "you shouldn't have the suid bit on this executable", which is
frustrating 'cause I haven't GOT the suid bit on that executable, it
inherited it from its parent process, which DOES explicitly set the $PATH and
blank most of the environment variables and other fun stuff...)
By the way, anybody who knows why samba goes postal if you change the
hostname of the box while it's running, please explain it to me. It's happy
once HUPed, then again it execs itself. (Not nmbd. smbd. Why does it CARE?
And sshd has the most amazing timeouts if it can't do a reverse dns lookup
on the incoming IP, even if I tell it not to log!)
Apache has a similar problem, and HUP-ing it interrupts in-progress
transfers, which could be very large files, 'cause it execs itself. I made
that happy by telling it its host name was a dot notation IP address,
although that does mean that logging into a password protected web page using
the host name forces you to log in twice (again when it switches you to
http://1.2.3.4/blah...)
Fun, isn't it? :)
Alan's right. We DO need a rant tag.
Rob
Rob Landley writes:
> Off the top of my head, fun things you can't do suid root:
...
> ps (What the...? Worked in Red Hat 7, but not in suse 7.1.
> Huh? "suid-to apache ps ax" works fine, though...)
The ps command used to require setuid root. People would set the
bit by habit.
> I keep bumping into more of these all the time. Often it's fun
> little warnings "you shouldn't have the suid bit on this
> executable", which is frustrating 'cause I haven't GOT the suid bit
> on that executable, it inherited it from its parent process, which
> DOES explicitly set the $PATH and blank most of the environment
> variables and other fun stuff...)
Oh, cry me a river. You can set the RUID, EUID, SUID, and FUID
in that same parent process or after you fork().
Since you didn't set all the UID values, I have to wonder what
else you forgot to do. Maybe you shouldn't be messing with
setuid programming.
On Thursday 05 July 2001 21:45, Albert D. Cahalan wrote:
> Oh, cry me a river. You can set the RUID, EUID, SUID, and FUID
> in that same parent process or after you fork().
Okay, I'll bite.
The file user ID is fine, the effective user ID is what the suid bit sets to
root of course, the saved user id is irrelevant to this (haven't encountered
something that actually cares about it yet, and yes I have been checking
source code when I bump into a problem).
But the actual uid (real user ID) ain't root, and an euid of root doesn't let
me change the uid itself to root, or at least I haven't figured out how.
(And haven't really tried: there are some things that might conceivably care
whether you really are root or not, but the samba change password command
isn't one of them. I have a password protected cgi accessed via ssl which
allows the manipulation of a limited subset of samba users, and the samba
tool will happily let me change anybody's password as suid root. But to add
a user, the script has to append an entry to the file manually and then
change the password from "racecondition" (which it is) to whatever the user's
password should be. I could patch and ship nonstandard samba binaries, but
that makes automatic upgrades problematic. (And samba, being a net
accessable server, REALLY needs to be kept up to date.))
Do you have a code example of how a program with euid root can change its
actual uid (which several programs check when they should be checking euid,
versions of dhcpcd before I complained about it case in point)?
Some of it's misguided "policy", assuming that the suid bit is on the
executable itself instead of its parent process. A check and an error "Thou
shalt not set this suid root" is fairly common on things that can be securely
run from a daemon running AS root. So apparently, the obvious way to fix it
is to relax the security restrictions even MORE, which is silly.
> Since you didn't set all the UID values, I have to wonder what
> else you forgot to do. Maybe you shouldn't be messing with
> setuid programming.
Ah, the BSD attitude. If you don't already know it, you should die rather
than try to learn it. Anybody who isn't perfect should leave us alone, we
LIKE our user base small. :)
Following this logic, nobody should use Linux because the kernel has
repeatedly shipped with holes allowing people to hack root, gaping big holes
like the insmod `;rm -rf /` thing last year. Apparently we should all be
using an early 90's version of netware or some kind of embedded system
audited for stack overflows and burned in ROM...
Rob
(Reference dilbert: "Here's a quarter kid, go buy yourself a real computer."
That's a nice way to recruit new users to help politically support decss or
convince video card manufacturers to release source code to their 3d drivers,
winmodems, funky encryption in USB audio, slipping registration stuff in the
ATA spec...)
Rob Landley <[email protected]> writes:
> Do you have a code example of how a program with euid root can change its
> actual uid (which several programs check when they should be checking euid,
> versions of dhcpcd before I complained about it case in point)?
Ummm... setuid(2)?
Works for me...
-Doug
--
The rain man gave me two cures; he said jump right in,
The first was Texas medicine--the second was just railroad gin,
And like a fool I mixed them, and it strangled up my mind,
Now people just get uglier, and I got no sense of time... --Dylan
On Friday 06 July 2001 11:17, Doug McNaught wrote:
> Rob Landley <[email protected]> writes:
> > Do you have a code example of how a program with euid root can change its
> > actual uid (which several programs check when they should be checking
> > euid, versions of dhcpcd before I complained about it case in point)?
>
> Ummm... setuid(2)?
>
> Works for me...
Albert Calahan cleared this up for me in email. I thought that euid 0
wouldn't let you actually setuid(0) for security reasons. (Otherwise the
distinction between the two of them seemed kind of pointless, which I must
admit I'm now officially confused about, and likely to spend an evening with
google over.)
Rob
>More interestingly, it changes the operation of SAK in two ways:
>(a) It does less, namely will not kill processes with uid 0.
I think this is bad for security.
(I assume you meant euid 0, not ruid 0. Using the real uid
for access control decisions is a very odd thing to do.)