if try to find problem on userspace, i used linux 5.13rc6 on old android 7 cm14.1, not aosp android 11. http://git.osdn.net/view?p=android-x86/system-core.git%3Ba=blob%3Bf=init/ser...
457 if (!seclabel_.empty()) { 458 if (setexeccon(seclabel_.c_str()) < 0) { 459 ERROR("cannot setexeccon('%s'): %s\n", 460 seclabel_.c_str(), strerror(errno)); 461 _exit(127); 462 } 463 }
2021-06-15 6:50 GMT+08:00, Kees Cook keescook@chromium.org:
On Tue, Jun 15, 2021 at 02:46:19AM +0800, youling 257 wrote:
I test this patch cause "init: cannot setexeccon(u:r:ueventd:s0) operation not permitted. init ctrl_write_limited.
Thanks for testing!
This appears to come from here: https://github.com/aosp-mirror/platform_system_core/blob/master/init/service...
In setexeccon(), I see (pid=0, attr="exec"):
fd = openattr(pid, attr, O_RDWR | O_CLOEXEC);... ret = write(fd, context2, strlen(context2) + 1); ... close(fd);
and openattr() is doing: ... rc = asprintf(&path, "/proc/thread-self/attr/%s", attr); if (rc < 0) return -1; fd = open(path, flags | O_CLOEXEC); ...
I'm not sure how the above could fail. (mm_access() always allows introspection...)
The only way I can understand the check failing is if a process did:
open, exec, write
But setexeccon() is not doing anything between the open and the write...
I will keep looking...
-Kees
-- Kees Cook