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userns: allow killing tasks in your own or child userns

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Changelog:
	Dec  8: Fixed bug in my check_kill_permission pointed out by
	        Eric Biederman.
	Dec 13: Apply Eric's suggestion to pass target task into kill_ok_by_cred()
	        for clarity
	Dec 31: address comment by Eric Biederman:
		don't need cred/tcred in check_kill_permission.
	Jan  1: use const cred struct.
	Jan 11: Per Bastian Blank's advice, clean up kill_ok_by_cred().
	Feb 16: kill_ok_by_cred: fix bad parentheses
	Feb 23: per akpm, let compiler inline kill_ok_by_cred

Signed-off-by: Serge E. Hallyn <serge.hallyn@canonical.com>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: Daniel Lezcano <daniel.lezcano@free.fr>
Acked-by: David Howells <dhowells@redhat.com>
Cc: James Morris <jmorris@namei.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Serge E. Hallyn 2011-03-23 16:43:19 -07:00 committed by Linus Torvalds
parent bb96a6f50b
commit 39fd33933b
1 changed files with 22 additions and 8 deletions
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30
kernel/signal.c
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@ -635,6 +635,27 @@ static inline bool si_fromuser(const struct siginfo *info)
(!is_si_special(info) && SI_FROMUSER(info));
}
/*
* called with RCU read lock from check_kill_permission()
*/
static int kill_ok_by_cred(struct task_struct *t)
{
const struct cred *cred = current_cred();
const struct cred *tcred = __task_cred(t);
if (cred->user->user_ns == tcred->user->user_ns &&
(cred->euid == tcred->suid ||
cred->euid == tcred->uid ||
cred->uid == tcred->suid ||
cred->uid == tcred->uid))
return 1;
if (ns_capable(tcred->user->user_ns, CAP_KILL))
return 1;
return 0;
}
/*
* Bad permissions for sending the signal
* - the caller must hold the RCU read lock
@ -642,7 +663,6 @@ static inline bool si_fromuser(const struct siginfo *info)
static int check_kill_permission(int sig, struct siginfo *info,
struct task_struct *t)
{
const struct cred *cred, *tcred;
struct pid *sid;
int error;
@ -656,14 +676,8 @@ static int check_kill_permission(int sig, struct siginfo *info,
if (error)
return error;
cred = current_cred();
tcred = __task_cred(t);
if (!same_thread_group(current, t) &&
(cred->euid ^ tcred->suid) &&
(cred->euid ^ tcred->uid) &&
(cred->uid ^ tcred->suid) &&
(cred->uid ^ tcred->uid) &&
!capable(CAP_KILL)) {
!kill_ok_by_cred(t)) {
switch (sig) {
case SIGCONT:
sid = task_session(t);