Show signal sender for SI_FROMUSER signals.

Suicide doesn't change:

  signal 6 (SIGABRT), code -6 (SI_TKILL), fault addr --------

But homicide now looks like this (this is `sleep 666` killed by
`kill -SEGV` as root:

  signal 11 (SIGSEGV), code 0 (SI_USER from pid 4446, uid 0), fault addr --------

Bug: http://b/78594105
Test: manual
Change-Id: I8c2feafba8cc5a3db85e8250004d428a464c5d9e

4 files changed, 54 insertions, 36 deletions

diff --git a/debuggerd/handler/debuggerd_handler.cpp b/debuggerd/handler/debuggerd_handler.cpp
index 05e6efa60..c07a34a70 100644
--- a/debuggerd/handler/debuggerd_handler.cpp
+++ b/debuggerd/handler/debuggerd_handler.cpp
@@ -169,24 +169,26 @@ static void log_signal_summary(const siginfo_t* info) {
     return;
   }
 
-  const char* signal_name = get_signame(info->si_signo);
-  bool has_address = signal_has_si_addr(info->si_signo, info->si_code);
-
-  // Many signals don't have an address.
+  // Many signals don't have an address or sender.
   char addr_desc[32] = "";  // ", fault addr 0x1234"
-  if (has_address) {
+  if (signal_has_si_addr(info)) {
     async_safe_format_buffer(addr_desc, sizeof(addr_desc), ", fault addr %p", info->si_addr);
   }
+  pid_t self_pid = __getpid();
+  char sender_desc[32] = {};  // " from pid 1234, uid 666"
+  if (signal_has_sender(info, self_pid)) {
+    get_signal_sender(sender_desc, sizeof(sender_desc), info);
+  }
 
   char main_thread_name[MAX_TASK_NAME_LEN + 1];
   if (!get_main_thread_name(main_thread_name, sizeof(main_thread_name))) {
     strncpy(main_thread_name, "<unknown>", sizeof(main_thread_name));
   }
 
-  async_safe_format_log(
-      ANDROID_LOG_FATAL, "libc", "Fatal signal %d (%s), code %d (%s)%s in tid %d (%s), pid %d (%s)",
-      info->si_signo, signal_name, info->si_code, get_sigcode(info->si_signo, info->si_code),
-      addr_desc, __gettid(), thread_name, __getpid(), main_thread_name);
+  async_safe_format_log(ANDROID_LOG_FATAL, "libc",
+                        "Fatal signal %d (%s), code %d (%s%s)%s in tid %d (%s), pid %d (%s)",
+                        info->si_signo, get_signame(info), info->si_code, get_sigcode(info),
+                        sender_desc, addr_desc, __gettid(), thread_name, self_pid, main_thread_name);
 }
 
 /*
diff --git a/debuggerd/libdebuggerd/include/libdebuggerd/utility.h b/debuggerd/libdebuggerd/include/libdebuggerd/utility.h
index 7b04e7192..7c5304e84 100644
--- a/debuggerd/libdebuggerd/include/libdebuggerd/utility.h
+++ b/debuggerd/libdebuggerd/include/libdebuggerd/utility.h
@@ -74,8 +74,10 @@ void read_with_default(const char* path, char* buf, size_t len, const char* defa
 
 void drop_capabilities();
 
-bool signal_has_si_addr(int si_signo, int si_code);
-const char* get_signame(int sig);
-const char* get_sigcode(int signo, int code);
+bool signal_has_sender(const siginfo_t*, pid_t caller_pid);
+bool signal_has_si_addr(const siginfo_t*);
+void get_signal_sender(char* buf, size_t n, const siginfo_t*);
+const char* get_signame(const siginfo_t*);
+const char* get_sigcode(const siginfo_t*);
 
 #endif // _DEBUGGERD_UTILITY_H
diff --git a/debuggerd/libdebuggerd/tombstone.cpp b/debuggerd/libdebuggerd/tombstone.cpp
index af8072e76..e11be1ea7 100644
--- a/debuggerd/libdebuggerd/tombstone.cpp
+++ b/debuggerd/libdebuggerd/tombstone.cpp
@@ -102,18 +102,24 @@ static void dump_probable_cause(log_t* log, const siginfo_t* si) {
   if (!cause.empty()) _LOG(log, logtype::HEADER, "Cause: %s\n", cause.c_str());
 }
 
-static void dump_signal_info(log_t* log, const siginfo_t* si) {
+static void dump_signal_info(log_t* log, const ThreadInfo& thread_info) {
   char addr_desc[32]; // ", fault addr 0x1234"
-  if (signal_has_si_addr(si->si_signo, si->si_code)) {
-    snprintf(addr_desc, sizeof(addr_desc), "%p", si->si_addr);
+  if (signal_has_si_addr(thread_info.siginfo)) {
+    snprintf(addr_desc, sizeof(addr_desc), "%p", thread_info.siginfo->si_addr);
   } else {
     snprintf(addr_desc, sizeof(addr_desc), "--------");
   }
 
-  _LOG(log, logtype::HEADER, "signal %d (%s), code %d (%s), fault addr %s\n", si->si_signo,
-       get_signame(si->si_signo), si->si_code, get_sigcode(si->si_signo, si->si_code), addr_desc);
+  char sender_desc[32] = {};  // " from pid 1234, uid 666"
+  if (signal_has_sender(thread_info.siginfo, thread_info.pid)) {
+    get_signal_sender(sender_desc, sizeof(sender_desc), thread_info.siginfo);
+  }
+
+  _LOG(log, logtype::HEADER, "signal %d (%s), code %d (%s%s), fault addr %s\n",
+       thread_info.siginfo->si_signo, get_signame(thread_info.siginfo),
+       thread_info.siginfo->si_code, get_sigcode(thread_info.siginfo), sender_desc, addr_desc);
 
-  dump_probable_cause(log, si);
+  dump_probable_cause(log, thread_info.siginfo);
 }
 
 static void dump_thread_info(log_t* log, const ThreadInfo& thread_info) {
@@ -412,7 +418,7 @@ static bool dump_thread(log_t* log, BacktraceMap* map, Memory* process_memory,
   dump_thread_info(log, thread_info);
 
   if (thread_info.siginfo) {
-    dump_signal_info(log, thread_info.siginfo);
+    dump_signal_info(log, thread_info);
   }
 
   if (primary_thread) {
@@ -442,7 +448,7 @@ static bool dump_thread(log_t* log, BacktraceMap* map, Memory* process_memory,
     if (map) {
       uint64_t addr = 0;
       siginfo_t* si = thread_info.siginfo;
-      if (signal_has_si_addr(si->si_signo, si->si_code)) {
+      if (signal_has_si_addr(si)) {
         addr = reinterpret_cast<uint64_t>(si->si_addr);
       }
       dump_all_maps(log, map, process_memory, addr);
diff --git a/debuggerd/libdebuggerd/utility.cpp b/debuggerd/libdebuggerd/utility.cpp
index 1ad180073..1f6f3c803 100644
--- a/debuggerd/libdebuggerd/utility.cpp
+++ b/debuggerd/libdebuggerd/utility.cpp
@@ -254,13 +254,13 @@ void drop_capabilities() {
   }
 }
 
-bool signal_has_si_addr(int si_signo, int si_code) {
+bool signal_has_si_addr(const siginfo_t* si) {
   // Manually sent signals won't have si_addr.
-  if (si_code == SI_USER || si_code == SI_QUEUE || si_code == SI_TKILL) {
+  if (si->si_code == SI_USER || si->si_code == SI_QUEUE || si->si_code == SI_TKILL) {
     return false;
   }
 
-  switch (si_signo) {
+  switch (si->si_signo) {
     case SIGBUS:
     case SIGFPE:
     case SIGILL:
@@ -272,8 +272,16 @@ bool signal_has_si_addr(int si_signo, int si_code) {
   }
 }
 
-const char* get_signame(int sig) {
-  switch (sig) {
+bool signal_has_sender(const siginfo_t* si, pid_t caller_pid) {
+  return SI_FROMUSER(si) && (si->si_pid != 0) && (si->si_pid != caller_pid);
+}
+
+void get_signal_sender(char* buf, size_t n, const siginfo_t* si) {
+  snprintf(buf, n, " from pid %d, uid %d", si->si_pid, si->si_uid);
+}
+
+const char* get_signame(const siginfo_t* si) {
+  switch (si->si_signo) {
     case SIGABRT: return "SIGABRT";
     case SIGBUS: return "SIGBUS";
     case SIGFPE: return "SIGFPE";
@@ -290,11 +298,11 @@ const char* get_signame(int sig) {
   }
 }
 
-const char* get_sigcode(int signo, int code) {
+const char* get_sigcode(const siginfo_t* si) {
   // Try the signal-specific codes...
-  switch (signo) {
+  switch (si->si_signo) {
     case SIGILL:
-      switch (code) {
+      switch (si->si_code) {
         case ILL_ILLOPC: return "ILL_ILLOPC";
         case ILL_ILLOPN: return "ILL_ILLOPN";
         case ILL_ILLADR: return "ILL_ILLADR";
@@ -307,7 +315,7 @@ const char* get_sigcode(int signo, int code) {
       static_assert(NSIGILL == ILL_BADSTK, "missing ILL_* si_code");
       break;
     case SIGBUS:
-      switch (code) {
+      switch (si->si_code) {
         case BUS_ADRALN: return "BUS_ADRALN";
         case BUS_ADRERR: return "BUS_ADRERR";
         case BUS_OBJERR: return "BUS_OBJERR";
@@ -317,7 +325,7 @@ const char* get_sigcode(int signo, int code) {
       static_assert(NSIGBUS == BUS_MCEERR_AO, "missing BUS_* si_code");
       break;
     case SIGFPE:
-      switch (code) {
+      switch (si->si_code) {
         case FPE_INTDIV: return "FPE_INTDIV";
         case FPE_INTOVF: return "FPE_INTOVF";
         case FPE_FLTDIV: return "FPE_FLTDIV";
@@ -330,7 +338,7 @@ const char* get_sigcode(int signo, int code) {
       static_assert(NSIGFPE == FPE_FLTSUB, "missing FPE_* si_code");
       break;
     case SIGSEGV:
-      switch (code) {
+      switch (si->si_code) {
         case SEGV_MAPERR: return "SEGV_MAPERR";
         case SEGV_ACCERR: return "SEGV_ACCERR";
 #if defined(SEGV_BNDERR)
@@ -350,21 +358,21 @@ const char* get_sigcode(int signo, int code) {
       break;
 #if defined(SYS_SECCOMP) // Our glibc is too old, and we build this for the host too.
     case SIGSYS:
-      switch (code) {
+      switch (si->si_code) {
         case SYS_SECCOMP: return "SYS_SECCOMP";
       }
       static_assert(NSIGSYS == SYS_SECCOMP, "missing SYS_* si_code");
       break;
 #endif
     case SIGTRAP:
-      switch (code) {
+      switch (si->si_code) {
         case TRAP_BRKPT: return "TRAP_BRKPT";
         case TRAP_TRACE: return "TRAP_TRACE";
         case TRAP_BRANCH: return "TRAP_BRANCH";
         case TRAP_HWBKPT: return "TRAP_HWBKPT";
       }
-      if ((code & 0xff) == SIGTRAP) {
-        switch ((code >> 8) & 0xff) {
+      if ((si->si_code & 0xff) == SIGTRAP) {
+        switch ((si->si_code >> 8) & 0xff) {
           case PTRACE_EVENT_FORK:
             return "PTRACE_EVENT_FORK";
           case PTRACE_EVENT_VFORK:
@@ -387,7 +395,7 @@ const char* get_sigcode(int signo, int code) {
       break;
   }
   // Then the other codes...
-  switch (code) {
+  switch (si->si_code) {
     case SI_USER: return "SI_USER";
     case SI_KERNEL: return "SI_KERNEL";
     case SI_QUEUE: return "SI_QUEUE";