commit d3915c7b53b745c521046b0af2455b4db3251c54
author Elliott Hughes <enh@google.com> Mon Feb 08 16:24:46 2021 -0800
committer Elliott Hughes <enh@google.com> Tue Feb 09 17:13:09 2021 -0800
tree e7696b302bdabb3896d808101376cb5337a1fc88
parent 6d5662d22a38ca6200d6b6dd919204bc93dbaba8

Make fd overflow an abort.

On LP32, just abort if we're asked to handle an fd that's too big for
the `short` field in `struct FILE`. This is unreachable anyway because
the ulimit is 32Ki, and this will make issues far more noticeable if we
ever do increase that limit (which seems unlikely for LP32 devices).

Also rename __finit() to __FILE_init() to match __FILE_close().

Test: treehugger
Change-Id: I5db4d6c4529a1f558aff135b4dea071d73666be5

libc/stdio/stdio.cpp

diff --git a/libc/stdio/stdio.cpp b/libc/stdio/stdio.cpp
index 2b0e2b2..c429ff2 100644
--- a/libc/stdio/stdio.cpp
+++ b/libc/stdio/stdio.cpp
@@ -226,9 +226,13 @@
   _fwalk(__sflush);
 }
 
-static FILE* __finit(FILE* fp, int fd, int flags) {
+static FILE* __FILE_init(FILE* fp, int fd, int flags) {
   if (fp == nullptr) return nullptr;
 
+#if !defined(__LP64__)
+  if (fd > SHRT_MAX) __fortify_fatal("stdio: fd %d > SHRT_MAX", fd);
+#endif
+
   fp->_file = fd;
   android_fdsan_exchange_owner_tag(fd, 0, __get_file_tag(fp));
   fp->_flags = flags;
@@ -237,15 +241,6 @@
   fp->_write = __swrite;
   fp->_close = __sclose;
   _EXT(fp)->_seek64 = __sseek64;
-
-#if !defined(__LP64__)
-  if (fd > SHRT_MAX) {
-    errno = EMFILE;
-    fclose(fp);
-    return nullptr;
-  }
-#endif
-
   return fp;
 }
 
@@ -259,7 +254,7 @@
     return nullptr;
   }
 
-  FILE* fp = __finit(__sfp(), fd, flags);
+  FILE* fp = __FILE_init(__sfp(), fd, flags);
   if (fp == nullptr) {
     ErrnoRestorer errno_restorer;
     close(fd);
@@ -298,7 +293,7 @@
     fcntl(fd, F_SETFD, tmp | FD_CLOEXEC);
   }
 
-  return __finit(__sfp(), fd, flags);
+  return __FILE_init(__sfp(), fd, flags);
 }
 
 FILE* freopen(const char* file, const char* mode, FILE* fp) {
@@ -398,11 +393,11 @@
     }
   }
 
-  fp = __finit(fp, fd, flags);
+  __FILE_init(fp, fd, flags);
 
   // For append mode, O_APPEND sets the write position for free, but we need to
   // set the read position manually.
-  if (fp && (mode_flags & O_APPEND) != 0) __sseek64(fp, 0, SEEK_END);
+  if ((mode_flags & O_APPEND) != 0) __sseek64(fp, 0, SEEK_END);
 
   return fp;
 }