Messages in this thread | | | Date | Tue, 27 Nov 2007 10:53:05 -0600 | From | "Serge E. Hallyn" <> | Subject | Re: [PATCH] file capabilities: don't prevent signaling setuid root programs. |
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Quoting Andrew Morgan (morgan@kernel.org): > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > Serge, > > I still feel a bit uneasy about this. Looking ahead, with filesystem > capabilities, one can simulate this same situation with a setuid > 'non-root' program as follows: > > [morgan@computer ~]$ cat > test.c > main() > { > printf("sleeping (%u)\n", getpid()); > sleep(100); > printf("woke up\n"); > } > [morgan@computer ~]$ cc -o test test.c > [morgan@computer ~]$ chmod u+s ./test > [morgan@computer ~]$ ls -ltr test > - -rwsrwxr-x 1 morgan morgan 7090 Nov 26 20:01 test > [morgan@computer ~]$ setcap cap_net_raw+ep ~/test > [morgan@computer ~]$ getcap ~/test > /home/morgan/test = cap_net_raw+ep > [morgan@computer ~]$ su luser > Password: > [luser@computer morgan]$ ./test > sleeping (5935) > > <In another shell run by luser> > [luser@computer morgan]$ kill 5935 > bash: kill: (5935) - Operation not permitted > > Because of the euid=0 test, the piece of code you are adding will behave > differently in this situation. Is the root-behavior deserving of less > protection than this one?
I don't believe in entitlement :)
> To my eye they seem equivalent.
Not to mine. The one case is classic setuid root, the other exploits the new file capabilities - even if they don't actually add any privilege.
> Is there a compelling reason to include the euid==0 check?
Yes, because only setuid root fills your capability sets.
In fact I was wondering whether the check should be under a check for !SECURE_NOROOT. I think it should, but it only matters after your per-process securebits patch is reposted.
Would you prefer if the check were under a sysctl, so that those really using file caps could tutn off the setuid root exception? It also provies a more graceful path toward eventually getting rid of this legacy support.
thanks, -serge
> > Thanks > > Andrew > > Serge E. Hallyn wrote: > > This patch is needed to preserve legacy behavior when > > CONFIG_SECURITY_FILE_CAPABILITIES=y. Without this patch, xinit can't > > kill X, so manually starting X in runlevel 3 then exiting your window > > manager will not cause X to exit. > > > > thanks, > > -serge > > > >>From 81a6d780ad570f9a326fc27912ec0e373f5fa14f Mon Sep 17 00:00:00 2001 > > From: Serge E. Hallyn <serue@us.ibm.com> > > Date: Tue, 20 Nov 2007 08:47:35 +0000 > > Subject: [PATCH] file capabilities: don't prevent signaling setuid root programs. > > > > An unprivileged process must be able to kill a setuid root > > program started by the same user. This is legacy behavior > > needed for instance for xinit to kill X when the window manager > > exits. > > > > When an unprivileged user runs a setuid root program in !SECURE_NOROOT > > mode, fP, fI, and fE are set full on, so pP' and pE' are full on. > > Then cap_task_kill() prevents the user from signaling the setuid root > > task. This is a change in behavior compared to when > > !CONFIG_SECURITY_FILE_CAPABILITIES. > > > > This patch introduces a special check into cap_task_kill() just > > to check whether a non-root user is signaling a setuid root > > program started by the same user. If so, then signal is allowed. > > > > Changelog: > > Nov 26: move test up above CAP_KILL test as per Andrew > > Morgan's suggestion. > > > > Signed-off-by: Serge E. Hallyn <serue@us.ibm.com> > > --- > > security/commoncap.c | 9 +++++++++ > > 1 files changed, 9 insertions(+), 0 deletions(-) > > > > diff --git a/security/commoncap.c b/security/commoncap.c > > index 302e8d0..5bc1895 100644 > > --- a/security/commoncap.c > > +++ b/security/commoncap.c > > @@ -526,6 +526,15 @@ int cap_task_kill(struct task_struct *p, struct siginfo *info, > > if (info != SEND_SIG_NOINFO && (is_si_special(info) || SI_FROMKERNEL(info))) > > return 0; > > > > + /* > > + * Running a setuid root program raises your capabilities. > > + * Killing your own setuid root processes was previously > > + * allowed. > > + * We must preserve legacy signal behavior in this case. > > + */ > > + if (p->euid == 0 && p->uid == current->uid) > > + return 0; > > + > > /* sigcont is permitted within same session */ > > if (sig == SIGCONT && (task_session_nr(current) == task_session_nr(p))) > > return 0; > -----BEGIN PGP SIGNATURE----- > Version: GnuPG v1.2.6 (GNU/Linux) > > iD8DBQFHS5m/QheEq9QabfIRAmouAJkBBB0kXH57s9mvlgdG3XZhC0pZMwCfZUW3 > L4vJUkR4tgAh33GTqEquIqw= > =sKCy > -----END PGP SIGNATURE----- > - > To unsubscribe from this list: send the line "unsubscribe linux-security-module" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html - 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/
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