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gen_init_cpio: avoid stack overflow when expanding

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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>
This commit is contained in:
Kees Cook 2012-10-25 13:38:14 -07:00 committed by Linus Torvalds
parent fee0de7791
commit 20f1de659b
1 changed files with 21 additions and 18 deletions
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39
usr/gen_init_cpio.c
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@ -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 @@ static int cpio_mkfile(const char *name, const char *location,
static char *cpio_replace_env(char *new_location)
{
char expanded[PATH_MAX + 1];
char env_var[PATH_MAX + 1];
char *start;
char *end;
char expanded[PATH_MAX + 1];
char env_var[PATH_MAX + 1];
char *start;
char *end;
for (start = NULL; (start = strstr(new_location, "${")); ) {
end = strchr(start, '}');
if (start < end) {
*env_var = *expanded = '\0';
strncat(env_var, start + 2, end - start - 2);
strncat(expanded, new_location, start - new_location);
strncat(expanded, getenv(env_var), PATH_MAX);
strncat(expanded, end + 1, PATH_MAX);
strncpy(new_location, expanded, PATH_MAX);
} else
break;
}
for (start = NULL; (start = strstr(new_location, "${")); ) {
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;
return new_location;
}