commit f340a56d1c7aa469ccb4150521aba19f5c73dcf0
author Elliott Hughes <enh@google.com> Thu Sep 06 10:42:40 2018 -0700
committer Elliott Hughes <enh@google.com> Thu Sep 06 10:42:40 2018 -0700
tree cc41e09773b753e85fb7a503cd257cf808fea7c0
parent 74934aaf10d629de477095f0b92c467849f89638

Use strerror_r(3) for the printf family %m.

There's TLS space used for unknown errno values, and a call to printf
shouldn't clobber that. No-one will ever hit this in real life, but
since it's easily fixed...

Bug: http://b/112776560
Test: ran tests
Change-Id: I8c2437f2e5214e652119791d4e162a197b049d5b

libc/stdio/vfprintf.cpp

diff --git a/libc/stdio/vfprintf.cpp b/libc/stdio/vfprintf.cpp
index 8b247e9..d99d09c 100644
--- a/libc/stdio/vfprintf.cpp
+++ b/libc/stdio/vfprintf.cpp
@@ -453,7 +453,7 @@
       case 'n':
         __fortify_fatal("%%n not allowed on Android");
       case 'm':
-        cp = strerror(caller_errno);
+        cp = strerror_r(caller_errno, buf, sizeof(buf));
         goto string;
       case 'O':
         flags |= LONGINT;

libc/stdio/vfwprintf.cpp

diff --git a/libc/stdio/vfwprintf.cpp b/libc/stdio/vfwprintf.cpp
index 19cce17..dd51eec 100644
--- a/libc/stdio/vfwprintf.cpp
+++ b/libc/stdio/vfwprintf.cpp
@@ -439,7 +439,8 @@
         __fortify_fatal("%%n not allowed on Android");
       case 'm':
         free(convbuf);
-        convbuf = helpers::mbsconv(strerror(caller_errno), prec);
+        convbuf = helpers::mbsconv(strerror_r(caller_errno,
+                                              reinterpret_cast<char*>(buf), sizeof(buf)), prec);
         if (convbuf == nullptr) {
             fp->_flags |= __SERR;
             goto error;

tests/stdio_test.cpp

diff --git a/tests/stdio_test.cpp b/tests/stdio_test.cpp
index 4107a74..54b913a 100644
--- a/tests/stdio_test.cpp
+++ b/tests/stdio_test.cpp
@@ -2369,6 +2369,16 @@
   ASSERT_STREQ("<Invalid argument>", buf);
 }
 
+TEST(STDIO_TEST, printf_m_does_not_clobber_strerror) {
+  char buf[BUFSIZ];
+  const char* m = strerror(-1);
+  ASSERT_STREQ("Unknown error -1", m);
+  errno = -2;
+  snprintf(buf, sizeof(buf), "<%m>");
+  ASSERT_STREQ("<Unknown error -2>", buf);
+  ASSERT_STREQ("Unknown error -1", m);
+}
+
 TEST(STDIO_TEST, wprintf_m) {
   wchar_t buf[BUFSIZ];
   errno = 0;
@@ -2382,6 +2392,16 @@
   ASSERT_EQ(std::wstring(L"<Invalid argument>"), buf);
 }
 
+TEST(STDIO_TEST, wprintf_m_does_not_clobber_strerror) {
+  wchar_t buf[BUFSIZ];
+  const char* m = strerror(-1);
+  ASSERT_STREQ("Unknown error -1", m);
+  errno = -2;
+  swprintf(buf, sizeof(buf), L"<%m>");
+  ASSERT_EQ(std::wstring(L"<Unknown error -2>"), buf);
+  ASSERT_STREQ("Unknown error -1", m);
+}
+
 TEST(STDIO_TEST, fopen_append_mode_and_ftell) {
   TemporaryFile tf;
   SetFileTo(tf.filename, "0123456789");