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[fedora-virt] [PATCH] FAKECHROOT_CMD_SUBST patch (was: Re: Other fakechroot changes (was: Re: [PATCH] fakechroot doesn't handle chroot relative paths correctly))



Piotr,

I've rebased this patch to the latest version of fakechroot from SVN.
I wonder if you'd consider it?  It passes all tests, and we now use it
extensively in libguestfs[1] & febootstrap[2].

Original description:

On Mon, Mar 30, 2009 at 06:54:43PM +0100, Richard W.M. Jones wrote:
> Here's a patch that adds support for FAKECHROOT_CMD_SUBST.  We use it
> like this:
> 
>   FAKECHROOT_CMD_SUBST=/sbin/ldconfig=/bin/true fakechroot ...
> 
> The substituted command runs outside the chroot, so in the above case
> it's running the system /bin/true.
> 
> Also includes an extra test and documentation.

Signed-off-by: Richard W.M. Jones <rjones redhat com>

Rich.

[1] http://et.redhat.com/~rjones/libguestfs/

[2] http://et.redhat.com/~rjones/febootstrap/

-- 
Richard Jones, Emerging Technologies, Red Hat  http://et.redhat.com/~rjones
Read my programming blog: http://rwmj.wordpress.com
Fedora now supports 75 OCaml packages (the OPEN alternative to F#)
http://cocan.org/getting_started_with_ocaml_on_red_hat_and_fedora
Index: test/t/cmd-subst-pwd.sh
===================================================================
--- test/t/cmd-subst-pwd.sh	(revision 0)
+++ test/t/cmd-subst-pwd.sh	(revision 0)
@@ -0,0 +1,3 @@
+#!/bin/sh
+
+echo substituted

Property changes on: test/t/cmd-subst-pwd.sh
___________________________________________________________________
Added: svn:executable
   + *

Index: test/t/cmd-subst.t
===================================================================
--- test/t/cmd-subst.t	(revision 0)
+++ test/t/cmd-subst.t	(revision 0)
@@ -0,0 +1,37 @@
+#!/bin/sh
+
+. ./tap.sh
+
+plan 5
+
+rm -rf testtree
+
+./testtree.sh testtree
+test "`cat testtree/CHROOT`" = "testtree" || not
+ok "testtree"
+
+t=`./fakechroot.sh testtree /bin/pwd`
+test "$t" = "/" || not
+ok "fakechroot pwd is /"
+
+export FAKECHROOT_CMD_SUBST="/bin/pwd=$(pwd)/t/cmd-subst-pwd.sh"
+
+t=`./fakechroot.sh testtree /bin/pwd`
+test "$t" = "substituted" || not
+ok "fakechroot substituted pwd (1)"
+
+export FAKECHROOT_CMD_SUBST="/no/file=foo:/bin/pwd=$(pwd)/t/cmd-subst-pwd.sh"
+
+t=`./fakechroot.sh testtree /bin/pwd`
+test "$t" = "substituted" || not
+ok "fakechroot substituted pwd (2)"
+
+export FAKECHROOT_CMD_SUBST="/no/file=foo:/other/file=bar"
+
+t=`./fakechroot.sh testtree /bin/pwd`
+test "$t" = "/" || not
+ok "fakechroot not substituted pwd is /"
+
+rm -rf testtree
+
+end

Property changes on: test/t/cmd-subst.t
___________________________________________________________________
Added: svn:executable
   + *

Index: test/Makefile.am
===================================================================
--- test/Makefile.am	(revision 334)
+++ test/Makefile.am	(working copy)
@@ -2,6 +2,7 @@
 
 TESTS = \
     t/chroot.t \
+    t/cmd-subst.t \
     t/escape-nested-chroot.t \
     t/pwd.t \
     t/touch.t \
Index: src/libfakechroot.c
===================================================================
--- src/libfakechroot.c	(revision 334)
+++ src/libfakechroot.c	(working copy)
@@ -1467,7 +1467,38 @@
     return execve (path, argv, environ);
 }
 
+/* Parse the FAKECHROOT_CMD_SUBST environment variable (the first
+ * parameter) and if there is a match with filename, return the
+ * substitution in cmd_subst.  Returns non-zero if there was a match.
+ *
+ * FAKECHROOT_CMD_SUBST=cmd=subst:cmd=subst:...
+ */
+static int
+try_cmd_subst (char *env, const char *filename, char *cmd_subst)
+{
+    int len = strlen (filename), len2;
+    char *p;
 
+    if (env == NULL) return 0;
+
+    do {
+	p = strchrnul (env, ':');
+
+	if (strncmp (env, filename, len) == 0 && env[len] == '=') {
+	    len2 = p - &env[len+1];
+	    if (len2 >= FAKECHROOT_MAXPATH)
+		len2 = FAKECHROOT_MAXPATH - 1;
+	    strncpy (cmd_subst, &env[len+1], len2);
+	    cmd_subst[len2] = '\0';
+	    return 1;
+	}
+
+	env = p;
+    } while (*env++ != '\0');
+
+    return 0;
+}
+
 /* #include <unistd.h> */
 int execve (const char *filename, char *const argv [], char *const envp[])
 {
@@ -1479,32 +1510,16 @@
     char *env;
     char tmp[FAKECHROOT_MAXPATH], newfilename[FAKECHROOT_MAXPATH], argv0[FAKECHROOT_MAXPATH];
     char *ptr;
-    unsigned int i, j, n, len;
+    unsigned int i, j, n, len, r, newenvppos;
     size_t sizeenvp;
     char c;
     char *fakechroot_path, *fakechroot_ptr, fakechroot_buf[FAKECHROOT_MAXPATH];
     char *envkey[] = { "FAKECHROOT", "FAKECHROOT_BASE",
                        "FAKECHROOT_VERSION", "FAKECHROOT_EXCLUDE_PATH",
+                       "FAKECHROOT_CMD_SUBST",
                        "LD_LIBRARY_PATH", "LD_PRELOAD" };
+    const int nr_envkey = sizeof envkey / sizeof envkey[0];
 
-    strncpy(argv0, filename, FAKECHROOT_MAXPATH);
-
-    expand_chroot_path(filename, fakechroot_path, fakechroot_ptr, fakechroot_buf);
-    strcpy(tmp, filename);
-    filename = tmp;
-
-    if ((file = open(filename, O_RDONLY)) == -1) {
-        errno = ENOENT;
-        return -1;
-    }
-
-    i = read(file, hashbang, FAKECHROOT_MAXPATH-2);
-    close(file);
-    if (i == -1) {
-        errno = ENOENT;
-        return -1;
-    }
-
     if (next_execve == NULL) fakechroot_init();
 
     /* Scan envp and check its size */
@@ -1514,39 +1529,69 @@
     }
 
     /* Copy envp to newenvp */
-    newenvp = malloc( sizeenvp * sizeof (char *) + sizeof(envkey) );
+    newenvp = malloc( (sizeenvp + 1) * sizeof (char *) );
     if (newenvp == NULL) {
         errno = ENOMEM;
         return -1;
     }
-    for (ep = (char **)envp, i = 0; *ep != NULL; ++ep) {
-        for (j = 0; j < sizeof (envkey) / sizeof (char *); j++) {
+    for (ep = (char **) envp, newenvppos = 0; *ep != NULL; ++ep) {
+        for (j = 0; j < nr_envkey; j++) {
             len = strlen (envkey[j]);
             if (strncmp (*ep, envkey[j], len) == 0 && (*ep)[len] == '=')
                 goto skip;
         }
-        newenvp[i] = *ep;
-        i++;
+        newenvp[newenvppos] = *ep;
+        newenvppos++;
     skip: ;
     }
+    newenvp[newenvppos] = NULL;
 
+    strncpy(argv0, filename, FAKECHROOT_MAXPATH);
+
+    r = try_cmd_subst (getenv ("FAKECHROOT_CMD_SUBST"), filename, tmp);
+    if (r) {
+        filename = tmp;
+
+        /* FAKECHROOT_CMD_SUBST escapes the chroot.  newenvp here does
+         * not contain LD_PRELOAD and the other special environment
+         * variables.
+         */
+        return next_execve(filename, argv, newenvp);
+    }
+
+    expand_chroot_path(filename, fakechroot_path, fakechroot_ptr, fakechroot_buf);
+    strcpy(tmp, filename);
+    filename = tmp;
+
+    if ((file = open(filename, O_RDONLY)) == -1) {
+        errno = ENOENT;
+        return -1;
+    }
+
+    i = read(file, hashbang, FAKECHROOT_MAXPATH-2);
+    close(file);
+    if (i == -1) {
+        errno = ENOENT;
+        return -1;
+    }
+
     /* Add our variables to newenvp */
-    newenvp = realloc( newenvp, i * sizeof(char *) + sizeof(envkey) );
+    newenvp = realloc( newenvp, (newenvppos + nr_envkey + 1) * sizeof(char *) );
     if (newenvp == NULL) {
         errno = ENOMEM;
         return -1;
     }
-    for (j = 0; j < sizeof(envkey) / sizeof(char *); j++) {
+    for (j = 0; j < nr_envkey; j++) {
         env = getenv(envkey[j]);
         if (env != NULL) {
-            newenvp[i] = malloc(strlen(envkey[j]) + strlen(env) + 3);
-            strcpy(newenvp[i], envkey[j]);
-            strcat(newenvp[i], "=");
-            strcat(newenvp[i], env);
-            i++;
+            newenvp[newenvppos] = malloc(strlen(envkey[j]) + strlen(env) + 3);
+            strcpy(newenvp[newenvppos], envkey[j]);
+            strcat(newenvp[newenvppos], "=");
+            strcat(newenvp[newenvppos], env);
+            newenvppos++;
         }
     }
-    newenvp[i] = NULL;
+    newenvp[newenvppos] = NULL;
 
     /* No hashbang in argv */
     if (hashbang[0] != '#' || hashbang[1] != '!')
Index: man/fakechroot.pod
===================================================================
--- man/fakechroot.pod	(revision 334)
+++ man/fakechroot.pod	(working copy)
@@ -139,6 +139,21 @@
 The list of directories which are excluded from being chrooted.  The elements
 of list are separated with colon.
 
+=item B<FAKECHROOT_CMD_SUBST>
+
+A list of command substitutions.  If a program tries to execute one of
+the commands given (path relative to the chroot) then the substitute
+command runs instead (path to substitute command is not chrooted).
+
+For example:
+
+ FAKECHROOT_CMD_SUBST=/sbin/ldconfig=/tmp/ldconfig-wrapper
+
+will substitute C</tmp/ldconfig-wrapper> for C</sbin/ldconfig>.
+
+Give as many substitute commands as you want, separated by C<:>
+(colon) characters.
+
 =item B<LD_LIBRARY_PATH>, B<LD_PRELOAD>
 
 Fakechroot is implemented by wrapping system calls.  This is accomplished by

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