Commit c725ee54 authored Nov 12, 2013 by Michal Nazarewicz Committed by Linus Torvalds Nov 13, 2013

gen_init_cpio: avoid NULL pointer dereference and rework env expanding



getenv() may return NULL if given environment variable does not exist
which leads to NULL dereference when calling strncat.

Besides that, the environment variable name was copied to a temporary
env_var buffer, but this copying can be avoided by simply using the input
string.

Lastly, the whole loop can be greatly simplified by using the snprintf
function instead of the playing with strncat.

 By the way, the current implementation allows a recursive variable
 expansion, as in:

   $ echo 'out ${A} out ' | A='a ${B} a' B=b /tmp/a
   out a b a out

 I'm assuming this is just a side effect and not a conscious decision
 (especially as this may lead to infinite loop), but I didn't want to
 change this behaviour without consulting.

 If the current behaviour is deamed incorrect, I'll be happy to send
 a patch without recursive processing.

Signed-off-by: Michal Nazarewicz <mina86@mina86.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Jesper Juhl <jj@codesealer.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 0ca43435

usr/gen_init_cpio.c

+9 −18

Original line number	Diff line number	Diff line
		@@ -382,24 +382,15 @@ error:
		static char cpio_replace_env(char new_location)
		{
		char expanded[PATH_MAX + 1];
		char env_var[PATH_MAX + 1];
		char *start;
		char *end;

		for (start = NULL; (start = strstr(new_location, "${")); ) {
		end = strchr(start, '}');
		if (start < end) {
		env_var = expanded = '\0';
		strncat(env_var, start + 2, end - start - 2);
		strncat(expanded, new_location, start - new_location);
		strncat(expanded, getenv(env_var),
		PATH_MAX - strlen(expanded));
		strncat(expanded, end + 1,
		PATH_MAX - strlen(expanded));
		strncpy(new_location, expanded, PATH_MAX);
		new_location[PATH_MAX] = 0;
		} else
		break;
		char start, end, *var;

		while ((start = strstr(new_location, "${")) &&
		(end = strchr(start + 2, '}'))) {
		start = end = 0;
		var = getenv(start + 2);
		snprintf(expanded, sizeof expanded, "%s%s%s",
		new_location, var ? var : "", end + 1);
		strcpy(new_location, expanded);
		}

		return new_location;

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