[PATCH] Harden os.system

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[PATCH] Harden os.system

From: Bryan O'Sullivan <[e-mail]>

Add util.system function.  This is similar to os.system, but will
either succeed (if the process finishes with a zero exit code) or raise
a util.CommandError (if the process exits uncleanly or is killed by
a signal).

Add util.explain_exit function.  This tends to be ubiquitous in code
that calls other processes, and must describe what has gone wrong.

Change some uses of os.system over to util.system.

manifest hash: e3bf4adcac5b915432ec0af00efdbcef86bea4b1
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mercurial/commands.py

@@ -291,7 +291,7 b' def clone(ui, source, dest = None, **opt'
 
         if link:
             ui.debug("copying by hardlink\n")
-            os.system("cp -al %s/.hg .hg" % source)
+            util.system("cp -al %s/.hg .hg" % source)
             try:
                 os.remove(".hg/dirstate")
             except: pass
@@ -871,6 +871,8 b' def dispatch(args):'
             return r
         else:
             return d()
+    except util.CommandError, inst:
+        u.warn("abort: %s\n" % inst.args)
     except hg.RepoError, inst:
         u.warn("abort: ", inst, "!\n")
     except SignalInterrupt:

mercurial/ui.py

@@ -5,7 +5,7 b''
 # This software may be used and distributed according to the terms
 # of the GNU General Public License, incorporated herein by reference.
 
-import os, sys, re, ConfigParser
+import os, sys, re, ConfigParser, util
 
 class ui:
     def __init__(self, verbose=False, debug=False, quiet=False,
@@ -78,10 +78,7 b' class ui:'
         f.close()
 
         editor = os.environ.get("HGEDITOR") or os.environ.get("EDITOR", "vi")
-        r = os.system("%s %s" % (editor, name))
-
-        if r:
-            raise "Edit failed!"
+        util.system("%s %s" % (editor, name), errprefix = "edit failed")
 
         t = open(name).read()
         t = re.sub("(?m)^HG:.*\n", "", t)

mercurial/util.py

@@ -7,6 +7,29 b''
 
 import os
 
+class CommandError(Exception): pass
+
+def explain_exit(code):
+    """return a 2-tuple (desc, code) describing a process's status"""
+    if os.WIFEXITED(code):
+        val = os.WEXITSTATUS(code)
+        return "exited with status %d" % val, val
+    elif os.WIFSIGNALED(code):
+        val = os.WTERMSIG(code)
+        return "killed by signal %d" % val, val
+    elif os.WIFSTOPPED(code):
+        val = os.STOPSIG(code)
+        return "stopped by signal %d" % val, val
+    raise ValueError("invalid exit code")
+    
+def system(cmd, errprefix = "abort"):
+    """execute a shell command that must succeed"""
+    rc = os.system(cmd)
+    if rc:
+        errmsg = "%s: %s %s" % (errprefix, os.path.basename(cmd.split(None, 1)[0]),
+                                explain_exit(rc)[0])
+        raise CommandError(errmsg)
+
 def rename(src, dst):
     try:
         os.rename(src, dst)