[PATCH] Fix readlink calls in GDB

[Pedro Alves <palves@redhat.com>]

This is largely based on a patch Maxime sent me, to fix readlink calls
in GDB.

Several readlink calls in gdb are wrong.  readlink doesn't append the
terminating nul, so if we're going to need to do that, we need to pass
'sizeof (buf) - 1' as buffer size.

See:

https://www.securecoding.cert.org/confluence/display/seccode/POS30-C.+Use+the+readlink%28%29+function+properly

Tested on x86_64 Fedora 17, and checked in.

gdb/
2012-11-26  Maxime Villard  <rustyBSD@gmx.fr>
	    Pedro Alves  <palves@redhat.com>

	* common/linux-osdata.c (linux_xfer_osdata_fds): Decrease buffer
	size parameter passed to readlink by one byte.
	* fbsd-nat.c (fbsd_pid_to_exec_file): Ditto.
	* linux-nat.c (linux_child_pid_to_exec_file): Ditto.
	* nbsd-nat.c (nbsd_pid_to_exec_file): Ditto.
	* inf-child.c (inf_child_fileio_readlink): Decrease local buffer's
	size by one byte.

gdb/gdbserver/
2012-11-26  Maxime Villard  <rustyBSD@gmx.fr>

	* hostio.c (handle_readlink): Decrease buffer size
	parameter passed to readlink by one byte.
---
 gdb/common/linux-osdata.c |    2 +-
 gdb/fbsd-nat.c            |    2 +-
 gdb/gdbserver/hostio.c    |    2 +-
 gdb/inf-child.c           |    2 +-
 gdb/linux-nat.c           |    2 +-
 gdb/nbsd-nat.c            |    2 +-
 6 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/gdb/common/linux-osdata.c b/gdb/common/linux-osdata.c
index d54f9d3..b275495 100644
--- a/gdb/common/linux-osdata.c
+++ b/gdb/common/linux-osdata.c
@@ -737,7 +737,7 @@ linux_xfer_osdata_fds (gdb_byte *readbuf,
 			    continue;
 
 			  fdname = xstrprintf ("%s/%s", pathname, dp2->d_name);
-			  rslt = readlink (fdname, buf, 1000);
+			  rslt = readlink (fdname, buf, sizeof (buf) - 1);
 			  if (rslt >= 0)
 			    buf[rslt] = '\0';
 
diff --git a/gdb/fbsd-nat.c b/gdb/fbsd-nat.c
index 254a01a..5eaecdd 100644
--- a/gdb/fbsd-nat.c
+++ b/gdb/fbsd-nat.c
@@ -55,7 +55,7 @@ fbsd_pid_to_exec_file (int pid)
 #endif
 
   path = xstrprintf ("/proc/%d/file", pid);
-  if (readlink (path, buf, MAXPATHLEN) == -1)
+  if (readlink (path, buf, MAXPATHLEN - 1) == -1)
     {
       xfree (buf);
       buf = NULL;
diff --git a/gdb/gdbserver/hostio.c b/gdb/gdbserver/hostio.c
index 72e334c..e89e100 100644
--- a/gdb/gdbserver/hostio.c
+++ b/gdb/gdbserver/hostio.c
@@ -483,7 +483,7 @@ handle_readlink (char *own_buf, int *new_packet_len)
       return;
     }
 
-  ret = readlink (filename, linkname, sizeof linkname);
+  ret = readlink (filename, linkname, sizeof (linkname) - 1);
   if (ret == -1)
     {
       hostio_error (own_buf);
diff --git a/gdb/inf-child.c b/gdb/inf-child.c
index ae2dd1e..3530e75 100644
--- a/gdb/inf-child.c
+++ b/gdb/inf-child.c
@@ -346,7 +346,7 @@ inf_child_fileio_readlink (const char *filename, int *target_errno)
   /* We support readlink only on systems that also provide a compile-time
      maximum path length (MAXPATHLEN), at least for now.  */
 #if defined (HAVE_READLINK) && defined (MAXPATHLEN)
-  char buf[MAXPATHLEN];
+  char buf[MAXPATHLEN - 1];
   int len;
   char *ret;
 
diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c
index 45f7e24..f5ca977 100644
--- a/gdb/linux-nat.c
+++ b/gdb/linux-nat.c
@@ -4319,7 +4319,7 @@ linux_child_pid_to_exec_file (int pid)
   memset (name2, 0, MAXPATHLEN);
 
   sprintf (name1, "/proc/%d/exe", pid);
-  if (readlink (name1, name2, MAXPATHLEN) > 0)
+  if (readlink (name1, name2, MAXPATHLEN - 1) > 0)
     return name2;
   else
     return name1;
diff --git a/gdb/nbsd-nat.c b/gdb/nbsd-nat.c
index 14b562f..7f5df66 100644
--- a/gdb/nbsd-nat.c
+++ b/gdb/nbsd-nat.c
@@ -34,7 +34,7 @@ nbsd_pid_to_exec_file (int pid)
   char *path;
 
   path = xstrprintf ("/proc/%d/exe", pid);
-  if (readlink (path, buf, MAXPATHLEN) == -1)
+  if (readlink (path, buf, MAXPATHLEN - 1) == -1)
     {
       xfree (buf);
       buf = NULL;