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.
Signed-off-by: Serge E. Hallyn <[email protected]>
Reviewed-by: "Eric W. Biederman" <[email protected]>
---
kernel/signal.c | 36 ++++++++++++++++++++++++++++--------
1 files changed, 28 insertions(+), 8 deletions(-)
diff --git a/kernel/signal.c b/kernel/signal.c
index 4e3cff1..6a12eae 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -636,13 +636,39 @@ static inline bool si_fromuser(const struct siginfo *info)
}
/*
+ * called with RCU read lock from check_kill_permission()
+ */
+static inline 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) {
+ /* 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
*/
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 +682,8 @@ 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);
--
1.7.0.4
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