Replace readlink calls with a safer version that guarantees NULL-termination.

This patch is part of a bigger patch that helps merging the breakpad code
with the modified version in Chromium OS.

Specifically, this patch makes the following changes:
1. Add a SafeReadLink function that wraps sys_readlink() to resolve a
   symbolic link but guarantees the result is NULL-terminated on success.
2. Refactor other source code to use SafeReadLink instead of readlink()
   or sys_readlink().

BUG=455
TEST=Tested the following:
1. Build on 32-bit and 64-bit Linux with gcc 4.4.3 and gcc 4.6.
2. Build on Mac OS X 10.6.8 with gcc 4.2 and clang 3.0 (with latest gmock).
3. All unit tests pass.
4. Run minidump-2-core to covnert a minidump file to a core file.
Review URL: http://breakpad.appspot.com/334001

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@896 4c0a9323-5329-0410-9bdc-e9ce6186880e

1 files changed, 4 insertions, 5 deletions

diff --git a/src/client/linux/crash_generation/crash_generation_server.cc b/src/client/linux/crash_generation/crash_generation_server.cc
index 2f7edb69..76c9d9cd 100644
--- a/src/client/linux/crash_generation/crash_generation_server.cc
+++ b/src/client/linux/crash_generation/crash_generation_server.cc
@@ -47,6 +47,7 @@
 #include "client/linux/minidump_writer/minidump_writer.h"
 #include "common/linux/eintr_wrapper.h"
 #include "common/linux/guid_creator.h"
+#include "common/linux/safe_readlink.h"
 
 static const char kCommandQuit = 'x';
 
@@ -79,12 +80,10 @@ GetInodeForProcPath(ino_t* inode_out, const char* path)
   assert(inode_out);
   assert(path);
 
-  char buf[256];
-  const ssize_t n = readlink(path, buf, sizeof(buf) - 1);
-  if (n == -1) {
+  char buf[PATH_MAX];
+  if (!SafeReadLink(path, buf)) {
     return false;
   }
-  buf[n] = 0;
 
   if (0 != memcmp(kSocketLinkPrefix, buf, sizeof(kSocketLinkPrefix) - 1)) {
     return false;
@@ -130,7 +129,7 @@ FindProcessHoldingSocket(pid_t* pid_out, ino_t socket_inode)
   for (std::vector<pid_t>::const_iterator
        i = pids.begin(); i != pids.end(); ++i) {
     const pid_t current_pid = *i;
-    char buf[256];
+    char buf[PATH_MAX];
     snprintf(buf, sizeof(buf), "/proc/%d/fd", current_pid);
     DIR* fd = opendir(buf);
     if (!fd)