Messages in this thread Patch in this message | | | Date | Mon, 26 Nov 2007 20:14:57 -0800 | From | Andrew Morgan <> | Subject | Re: [PATCH] file capabilities: don't prevent signaling setuid root programs. |
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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? To my eye they seem equivalent.
Is there a compelling reason to include the euid==0 check?
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)
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