debuggerd_handler: raise capabilities before running crash_dump.
Raise CapInh and CapAmb after forking to exec crash_dump, so that it
can ptrace us.
Bug: http://b/35174939
Test: debuggerd -b `pidof surfaceflinger`
Change-Id: I32567010a3603cfa494aae9dc0e3ce73fb86b590
diff --git a/debuggerd/handler/debuggerd_handler.cpp b/debuggerd/handler/debuggerd_handler.cpp
index 353f642..cb8f017 100644
--- a/debuggerd/handler/debuggerd_handler.cpp
+++ b/debuggerd/handler/debuggerd_handler.cpp
@@ -174,6 +174,41 @@
return (old_action.sa_flags & SA_SIGINFO) != 0;
}
+static void raise_caps() {
+ // Raise CapInh to match CapPrm, so that we can set the ambient bits.
+ __user_cap_header_struct capheader;
+ memset(&capheader, 0, sizeof(capheader));
+ capheader.version = _LINUX_CAPABILITY_VERSION_3;
+ capheader.pid = 0;
+
+ __user_cap_data_struct capdata[2];
+ if (capget(&capheader, &capdata[0]) == -1) {
+ fatal_errno("capget failed");
+ }
+
+ if (capdata[0].permitted != capdata[0].inheritable ||
+ capdata[1].permitted != capdata[1].inheritable) {
+ capdata[0].inheritable = capdata[0].permitted;
+ capdata[1].inheritable = capdata[1].permitted;
+
+ if (capset(&capheader, &capdata[0]) == -1) {
+ __libc_format_log(ANDROID_LOG_ERROR, "libc", "capset failed: %s", strerror(errno));
+ }
+ }
+
+ // Set the ambient capability bits so that crash_dump gets all of our caps and can ptrace us.
+ uint64_t capmask = capdata[0].inheritable;
+ capmask |= static_cast<uint64_t>(capdata[1].inheritable) << 32;
+ for (unsigned long i = 0; i < 64; ++i) {
+ if (capmask & (1 << i)) {
+ if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, i, 0, 0) != 0) {
+ __libc_format_log(ANDROID_LOG_ERROR, "libc", "failed to raise ambient capability %lu: %s",
+ i, strerror(errno));
+ }
+ }
+ }
+}
+
struct debugger_thread_info {
bool crash_dump_started;
pid_t crashing_tid;
@@ -217,10 +252,7 @@
close(pipefds[0]);
close(pipefds[1]);
- // Set all of the ambient capability bits we can, so that crash_dump can ptrace us.
- for (unsigned long i = 0; prctl(PR_CAPBSET_READ, i, 0, 0, 0) != -1; ++i) {
- prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, i, 0, 0);
- }
+ raise_caps();
char buf[10];
snprintf(buf, sizeof(buf), "%d", thread_info->crashing_tid);