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authorMarco Elver <elver@google.com>2021-07-05 10:44:52 +0200
committerPeter Zijlstra <peterz@infradead.org>2021-07-16 18:46:38 +0200
commit9d7a6c95f62bc335b62aaf9d50590122bd03a796 (patch)
tree793a71181113cab26c1fe6e23483de2e8372b484 /kernel
parent7fef2edf7cc753b51f7ccc74993971b0a9c81eca (diff)
downloadlinux-9d7a6c95f62bc335b62aaf9d50590122bd03a796.tar.bz2
perf: Fix required permissions if sigtrap is requested
If perf_event_open() is called with another task as target and perf_event_attr::sigtrap is set, and the target task's user does not match the calling user, also require the CAP_KILL capability or PTRACE_MODE_ATTACH permissions. Otherwise, with the CAP_PERFMON capability alone it would be possible for a user to send SIGTRAP signals via perf events to another user's tasks. This could potentially result in those tasks being terminated if they cannot handle SIGTRAP signals. Note: The check complements the existing capability check, but is not supposed to supersede the ptrace_may_access() check. At a high level we now have: capable of CAP_PERFMON and (CAP_KILL if sigtrap) OR ptrace_may_access(...) // also checks for same thread-group and uid Fixes: 97ba62b27867 ("perf: Add support for SIGTRAP on perf events") Reported-by: Dmitry Vyukov <dvyukov@google.com> Signed-off-by: Marco Elver <elver@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Dmitry Vyukov <dvyukov@google.com> Cc: <stable@vger.kernel.org> # 5.13+ Link: https://lore.kernel.org/r/20210705084453.2151729-1-elver@google.com
Diffstat (limited to 'kernel')
-rw-r--r--kernel/events/core.c25
1 files changed, 24 insertions, 1 deletions
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 464917096e73..c13730b7ac01 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -12158,10 +12158,33 @@ SYSCALL_DEFINE5(perf_event_open,
}
if (task) {
+ unsigned int ptrace_mode = PTRACE_MODE_READ_REALCREDS;
+ bool is_capable;
+
err = down_read_interruptible(&task->signal->exec_update_lock);
if (err)
goto err_file;
+ is_capable = perfmon_capable();
+ if (attr.sigtrap) {
+ /*
+ * perf_event_attr::sigtrap sends signals to the other
+ * task. Require the current task to also have
+ * CAP_KILL.
+ */
+ rcu_read_lock();
+ is_capable &= ns_capable(__task_cred(task)->user_ns, CAP_KILL);
+ rcu_read_unlock();
+
+ /*
+ * If the required capabilities aren't available, checks
+ * for ptrace permissions: upgrade to ATTACH, since
+ * sending signals can effectively change the target
+ * task.
+ */
+ ptrace_mode = PTRACE_MODE_ATTACH_REALCREDS;
+ }
+
/*
* Preserve ptrace permission check for backwards compatibility.
*
@@ -12171,7 +12194,7 @@ SYSCALL_DEFINE5(perf_event_open,
* perf_event_exit_task() that could imply).
*/
err = -EACCES;
- if (!perfmon_capable() && !ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS))
+ if (!is_capable && !ptrace_may_access(task, ptrace_mode))
goto err_cred;
}