Changelog:
Dec 8: Fixed bug in my check_kill_permission pointed out by
Eric Biederman.
To test:
1. Test killing tasks as usual. No change.
2. Clone a new user namespace without a new pidns.
a. You CAN kill -CONT tasks in your thread group but outside
your user ns.
b. You can NOT otherwise kill tasks outside your user_ns.
c. Inside your new userns, signal semantics are as normal
with respect to userids, CAP_KILL, and thread groups.
Signed-off-by: Serge E. Hallyn <serge.hallyn@xxxxxxxxxxxxx>
---
kernel/signal.c | 27 ++++++++++++++++++++++-----
1 files changed, 22 insertions(+), 5 deletions(-)
diff --git a/kernel/signal.c b/kernel/signal.c
index 4e3cff1..677025c 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -635,6 +635,27 @@ static inline bool si_fromuser(const struct siginfo *info)
(!is_si_special(info) && SI_FROMUSER(info));
}
+static inline int kill_ok_by_cred(struct cred *cred, struct cred *tcred)
+{
+ if (cred->user->user_ns != tcred->user->user_ns) {
+ /* userids are not equivalent - either you have the
+ capability to the target user ns or you don't */
+ if (ns_capable(tcred->user->user_ns, CAP_KILL))
+ return 1;
+ return 0;
+ }
+
+ /* same user namespace - usual credentials checks apply */
+ if ((cred->euid ^ tcred->suid) &&
+ (cred->euid ^ tcred->uid) &&
+ (cred->uid ^ tcred->suid) &&
+ (cred->uid ^ tcred->uid) &&
+ !ns_capable(tcred->user->user_ns, CAP_KILL))
+ return 0;
+
+ return 1;
+}
+
/*
* Bad permissions for sending the signal
* - the caller must hold the RCU read lock
@@ -659,11 +680,7 @@ static int check_kill_permission(int sig, struct siginfo *info,
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(cred, tcred)) {
switch (sig) {
case SIGCONT:
sid = task_session(t);
--
1.7.2.3
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