[bug-patch] [PATCH] avoid using stat.st_dev and st_ino members of uninitialized "outst"

[Jim Meyering]

Testing my recent changes, I found an unrelated used-uninitialized bug.
It did not look easy to abuse, since the affected data are used only in
determining whether a file has already been processed.

This fixes it:

I've deliberately left out the ChangeLog patch,
since they usually cause more trouble than they're worth.
(which is why I generate the ChangeLog from commit logs in
coreutils and other packages)

2011-02-07  Jim Meyering  <address@hidden>

        avoid using stat.st_dev and st_ino members of uninitialized "outst"
        This local variable is used in move_file, and *may* be initialized
        by the preceding call to spew_output.  However, when that call is
        skipped, move_file uses those members uninitialized.
        * src/patch.c (main): Initialize the st_size member to -1 to act
        as a witness.  Then, we can test whether an explicit stat/fstat is
        required just prior to calling move_file.


>From c24017d37d71ded8fc3466c8330014d92bbd59b7 Mon Sep 17 00:00:00 2001
From: Jim Meyering <address@hidden>
Date: Mon, 7 Feb 2011 19:07:34 +0100
Subject: [PATCH] avoid using stat.st_dev and st_ino members of uninitialized 
"outst"

This local variable is used in move_file, and *may* be initialized
by the preceding call to spew_output.  However, when that call is
skipped, move_file uses those members uninitialized.
* src/patch.c (main): Initialize the st_size member to -1 to act
as a witness.  Then, we can test whether an explicit stat/fstat is
required just prior to calling move_file.
---
 src/patch.c |   11 +++++++++++
 2 files changed, 19 insertions(+), 0 deletions(-)

diff --git a/src/patch.c b/src/patch.c
index 77be499..21740c9 100644
--- a/src/patch.c
+++ b/src/patch.c
@@ -105,6 +105,7 @@ main (int argc, char **argv)
     mode_t file_type;
     int outfd = -1;

+    outst.st_size = -1;
     exit_failure = 2;
     program_name = argv[0];
     init_time ();
@@ -500,6 +501,16 @@ main (int argc, char **argv)
                        set_file_attributes (TMPOUTNAME, attr, inname, &instat,
                                             mode, &new_time);

+                     /* We may have useful data in outst, via spew_output.
+                        If not, get it now, via the file descriptor when
+                        possible.  */
+                     if (outst.st_size == -1)
+                       {
+                         if (0 <= outfd
+                             ? fstat (outfd, &outst)
+                             : stat (TMPOUTNAME, &outst))
+                           fatal ("failed to stat %s", quotearg (TMPOUTNAME));
+                       }
                      move_file (TMPOUTNAME, &TMPOUTNAME_needs_removal, &outst,
                                 outname, mode, backup);

--
1.7.4.2.g597a6