gen_init_cpio: avoid stack overflow when expanding

Fix possible overflow of the buffer used for expanding environment
variables when building file list.  In the extremely unlikely case of an
attacker having control over the environment variables visible to
gen_init_cpio, control over the contents of the file gen_init_cpio parses,
and gen_init_cpio was built without compiler hardening, the attacker can
gain arbitrary execution control via a stack buffer overflow.

$ cat usr/crash.list
file foo ${BIG}${BIG}${BIG}${BIG}${BIG}${BIG} 0755 0 0
$ BIG=$(perl -e 'print "A" x 4096;') ./usr/gen_init_cpio usr/crash.list
*** buffer overflow detected ***: ./usr/gen_init_cpio terminated

This also replaces the space-indenting with tabs.

Patch based on existing fix extracted from grsecurity.

Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Michal Marek <mmarek@suse.cz>
Cc: Brad Spengler <spender@grsecurity.net>
Cc: PaX Team <pageexec@freemail.hu>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/usr/gen_init_cpio.c b/usr/gen_init_cpio.c
index af0f22fb1ef71e6dc94c620873bc3241c2883430..aca6edcbbc6fa09113389e87b3e76a55a871da98 100644 (file)
--- a/usr/gen_init_cpio.c
+++ b/usr/gen_init_cpio.c
@@ -303,7 +303,7 @@ static int cpio_mkfile(const char *name, const char *location,
        int retval;
        int rc = -1;
        int namesize;
-       int i;
+       unsigned int i;
 
        mode |= S_IFREG;
 
@@ -381,25 +381,28 @@ 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, "${")); ) {
-               end = strchr(start, '}');
-               if (start < end) {
-                       *env_var = *expanded = '\0';
-                       strncat(env_var, start + 2, end - start - 2);
-                       strncat(expanded, new_location, start - new_location);
-                       strncat(expanded, getenv(env_var), PATH_MAX);
-                       strncat(expanded, end + 1, PATH_MAX);
-                       strncpy(new_location, expanded, PATH_MAX);
-               } else
-                       break;
-       }
-
-       return new_location;
+       char expanded[PATH_MAX + 1];
+       char env_var[PATH_MAX + 1];
+       char *start;
+       char *end;
+
+       for (start = NULL; (start = strstr(new_location, "${")); ) {
+               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;
+       }
+
+       return new_location;
 }