Commit 20f1de65 authored Oct 25, 2012 by Kees Cook Committed by Linus Torvalds Oct 25, 2012

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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent fee0de77

usr/gen_init_cpio.c

+23 −20

Original line number	Original line	Diff line number	Diff line
	@@ -303,7 +303,7 @@ static int cpio_mkfile(const char name, const char location,
	int retval;		int retval;
	int rc = -1;		int rc = -1;
	int namesize;		int namesize;
	int i;		unsigned int i;

	mode \|= S_IFREG;		mode \|= S_IFREG;

	@@ -392,9 +392,12 @@ static char cpio_replace_env(char new_location)
	env_var = expanded = '\0';		env_var = expanded = '\0';
	strncat(env_var, start + 2, end - start - 2);		strncat(env_var, start + 2, end - start - 2);
	strncat(expanded, new_location, start - new_location);		strncat(expanded, new_location, start - new_location);
	strncat(expanded, getenv(env_var), PATH_MAX);		strncat(expanded, getenv(env_var),
	strncat(expanded, end + 1, PATH_MAX);		PATH_MAX - strlen(expanded));
			strncat(expanded, end + 1,
			PATH_MAX - strlen(expanded));
	strncpy(new_location, expanded, PATH_MAX);		strncpy(new_location, expanded, PATH_MAX);
			new_location[PATH_MAX] = 0;
	} else		} else
	break;		break;
	}		}

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