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snd_user_file: avoid use wordexp

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As suggested in POSIX[1], wordexp might execute the shell. If the libc
implementation does so, it will break the firefox sandbox which does
not allow exec. This happened on Alpine Linux with musl libc[2].

Since we cannot guarantee that the system wordexp implementation does
not execute shell, we cannot really use it, and need to implement the
~/ expansion ourselves.

We provide a configure option --with-wordexp for users that still may
need it, but we leave this off by default because wordexp is a large
attack vector and it is better to avoid it.

[1]: http://pubs.opengroup.org/onlinepubs/9699919799/functions/wordexp.html#tag_16_684_08
[2]: http://bugs.alpinelinux.org/issues/7454#note-2

Signed-off-by: Natanael Copa <ncopa@alpinelinux.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Natanael Copa 2017-07-14 18:47:05 +02:00 • committed by Takashi Iwai
parent adab355f35
commit cb34cee0d8
2 changed files with 75 additions and 9 deletions
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19
configure.ac
View file

@ -303,8 +303,25 @@ fi
AC_SUBST(ALSA_DEPLIBS)
dnl Check for use of wordexp...
AC_MSG_CHECKING(for use of wordexp)
AC_ARG_WITH(wordexp,
AS_HELP_STRING([--with-wordexp],
[Use wordexp when expanding configs (default = no)]),
[case "$withval" in
y|yes) wordexp=yes ;;
*) wordexp=no ;;
esac],)
if test "$wordexp" = "yes" ; then
AC_DEFINE(HAVE_WORDEXP, "1", [Enable use of wordexp])
AC_MSG_RESULT(yes)
AC_CHECK_HEADER([wordexp.h],[], [AC_MSG_ERROR([Couldn't find wordexp.h])])
else
AC_MSG_RESULT(no)
fi
dnl Check for headers
AC_CHECK_HEADERS([wordexp.h endian.h sys/endian.h sys/shm.h])
AC_CHECK_HEADERS([endian.h sys/endian.h sys/shm.h])
dnl Check for resmgr support...
AC_MSG_CHECKING(for resmgr support)

65
src/userfile.c
View file

@ -21,6 +21,7 @@
#include <config.h>
#include <string.h>
#include <errno.h>
#include <assert.h>
/**
* \brief Get the full file name
@ -32,14 +33,13 @@
* stores the first matchine one. The returned string is strdup'ed.
*/
#ifdef HAVE_WORDEXP_H
#ifdef HAVE_WORDEXP
#include <wordexp.h>
#include <assert.h>
int snd_user_file(const char *file, char **result)
{
wordexp_t we;
int err;
assert(file && result);
err = wordexp(file, &we, WRDE_NOCMD);
switch (err) {
@ -61,13 +61,62 @@ int snd_user_file(const char *file, char **result)
return 0;
}
#else /* !HAVE_WORDEXP_H */
/* just copy the string - would be nicer to expand by ourselves, though... */
#else /* !HAVE_WORDEX */
#include <sys/types.h>
#include <unistd.h>
#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
int snd_user_file(const char *file, char **result)
{
*result = strdup(file);
if (! *result)
int err;
size_t len;
char *buf = NULL;
assert(file && result);
*result = NULL;
/* expand ~/ if needed */
if (file[0] == '~' && file[1] == '/') {
const char *home = getenv("HOME");
if (home == NULL) {
struct passwd pwent, *p = NULL;
uid_t id = getuid();
size_t bufsize = 1024;
buf = malloc(bufsize);
if (buf == NULL)
goto out;
while ((err = getpwuid_r(id, &pwent, buf, bufsize, &p)) == ERANGE) {
char *newbuf;
bufsize += 1024;
if (bufsize < 1024)
break;
newbuf = realloc(buf, bufsize);
if (newbuf == NULL)
goto out;
buf = newbuf;
}
home = err ? "" : pwent.pw_dir;
}
len = strlen(home) + strlen(&file[2]) + 2;
*result = malloc(len);
if (*result)
snprintf(*result, len, "%s/%s", home, &file[2]);
} else {
*result = strdup(file);
}
out:
if (buf)
free(buf);
if (*result == NULL)
return -ENOMEM;
return 0;
}
#endif /* HAVE_WORDEXP_H */
#endif /* HAVE_WORDEXP */