On Wed, Aug 07, 2019 at 12:44:08PM -0700, Casey Schaufler wrote:
> The getsockopt SO_PEERSEC provides the LSM based security
> information for a single module, but for reasons of backward
> compatibility cannot include the information for multiple
> modules. A new option SO_PEERCONTEXT is added to report the
> security "context" of multiple modules using a "compound" format
>
> lsm1\0value\0lsm2\0value\0
>
> This is expected to be used by system services, including dbus-daemon.
> The exact format of a compound context has been the subject of
> considerable debate. This format was suggested by Simon McVittie,
> a dbus maintainer with a significant stake in the format being
> uasable.
>
> Signed-off-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
> ---
> [...]
> diff --git a/security/security.c b/security/security.c
> index 2f4a430a1126..0ea7ee27e331 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -2117,8 +2117,8 @@ int security_setprocattr(const char *lsm, const char *name, void *value,
> hlist_for_each_entry(hp, &security_hook_heads.setprocattr, list) {
> if (lsm != NULL && strcmp(lsm, hp->lsmid->lsm))
> continue;
> - if (lsm == NULL && *display != LSMBLOB_INVALID &&
> - *display != hp->lsmid->slot)
> + if (lsm == NULL && display != NULL &&
> + *display != LSMBLOB_INVALID && *display != hp->lsmid->slot)
> continue;
> return hp->hook.setprocattr(name, value, size);
> }
> @@ -2342,17 +2342,91 @@ int security_sock_rcv_skb(struct sock *sk, struct sk_buff *skb)
> EXPORT_SYMBOL(security_sock_rcv_skb);
>
> int security_socket_getpeersec_stream(struct socket *sock, char __user *optval,
> - int __user *optlen, unsigned len)
> + int __user *optlen, unsigned len,
> + int display)
> {
> - int display = lsm_task_display(current);
> struct security_hook_list *hp;
> + char *final = NULL;
> + char *cp;
> + char *tp;
> + int rc = 0;
> + unsigned finallen = 0;
> + unsigned llen;
> + unsigned clen = 0;
> + unsigned tlen;
Please move the case-specific variables into the case scope, like (and
expand type names):
case LSMBLOB_COMPOUND: {
unsigned int clen ...;
> +
> + switch (display) {
> + case LSMBLOB_DISPLAY:
> + rc = -ENOPROTOOPT;
> + display = lsm_task_display(current);
> + hlist_for_each_entry(hp,
> + &security_hook_heads.socket_getpeersec_stream,
> + list)
> + if (display == LSMBLOB_INVALID ||
> + display == hp->lsmid->slot) {
> + rc = hp->hook.socket_getpeersec_stream(sock,
> + &final, &finallen, len);
> + break;
> + }
> + break;
> + case LSMBLOB_COMPOUND:
> + /*
> + * A compound context, in the form [lsm\0value\0]...
> + */
> + hlist_for_each_entry(hp,
> + &security_hook_heads.socket_getpeersec_stream,
> + list) {
> + rc = hp->hook.socket_getpeersec_stream(sock, &cp, &clen,
> + len);
Is passing "len" here useful at all? It's kind of a lie, but nothing
else wouldn't also be a lie. :)
> + if (rc == -EINVAL || rc == -ENOPROTOOPT) {
> + rc = 0;
> + continue;
> + }
> + if (rc) {
> + kfree(final);
> + return rc;
> + }
> + /*
> + * Don't propogate trailing nul bytes.
typo: propagate
> + */
> + clen = strnlen(cp, clen) + 1;
> + llen = strlen(hp->lsmid->lsm) + 1;
> + tlen = llen + clen;
> + if (final)
> + tlen += finallen;
You can drop the "if (final)" since finallen is initialized to 0.
> + tp = kzalloc(tlen, GFP_KERNEL);
I'm not a huge fan of "c", "l", and "t" prefixes -- can you just make
these a little more self-documenting? cp and clen could be value and
value_len. llen could be lsm_name_len. tp and tlen could be tuple and
tuple_len. (And maybe final and finallen could be compound and
compound_len?)
> + if (tp == NULL) {
> + kfree(cp);
> + kfree(final);
> + return -ENOMEM;
> + }
> + if (final)
> + memcpy(tp, final, finallen);
> + memcpy(tp + finallen, hp->lsmid->lsm, llen);
> + memcpy(tp + finallen + llen, cp, clen);
> + kfree(cp);
> + if (final)
> + kfree(final);
Just kfree(final) is safe here -- kfree(NULL) is valid.
> + final = tp;
> + finallen = tlen;
> + }
> + if (final == NULL)
> + return -EINVAL;
> + break;
> + default:
> + return -EINVAL;
> + }
>
> - hlist_for_each_entry(hp, &security_hook_heads.socket_getpeersec_stream,
> - list)
> - if (display == LSMBLOB_INVALID || display == hp->lsmid->slot)
> - return hp->hook.socket_getpeersec_stream(sock, optval,
> - optlen, len);
> - return -ENOPROTOOPT;
> + if (finallen > len)
> + rc = -ERANGE;
> + else if (copy_to_user(optval, final, finallen))
> + rc = -EFAULT;
> +
> + if (put_user(finallen, optlen))
> + rc = -EFAULT;
> +
> + kfree(final);
> + return rc;
> }
Otherwise, looks good.
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
-Kees
>
> int security_socket_getpeersec_dgram(struct socket *sock, struct sk_buff *skb,
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index fcad2e3432d2..5e7d61754798 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -4923,10 +4923,8 @@ static int selinux_socket_sock_rcv_skb(struct sock *sk, struct sk_buff *skb)
> return err;
> }
>
> -static int selinux_socket_getpeersec_stream(struct socket *sock,
> - char __user *optval,
> - int __user *optlen,
> - unsigned int len)
> +static int selinux_socket_getpeersec_stream(struct socket *sock, char **optval,
> + int *optlen, unsigned int len)
> {
> int err = 0;
> char *scontext;
> @@ -4946,18 +4944,12 @@ static int selinux_socket_getpeersec_stream(struct socket *sock,
> if (err)
> return err;
>
> - if (scontext_len > len) {
> + if (scontext_len > len)
> err = -ERANGE;
> - goto out_len;
> - }
> -
> - if (copy_to_user(optval, scontext, scontext_len))
> - err = -EFAULT;
> + else
> + *optval = scontext;
>
> -out_len:
> - if (put_user(scontext_len, optlen))
> - err = -EFAULT;
> - kfree(scontext);
> + *optlen = scontext_len;
> return err;
> }
>
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index 7a30b8692b1e..40c75205a914 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -3919,28 +3919,29 @@ static int smack_socket_sock_rcv_skb(struct sock *sk, struct sk_buff *skb)
> *
> * returns zero on success, an error code otherwise
> */
> -static int smack_socket_getpeersec_stream(struct socket *sock,
> - char __user *optval,
> - int __user *optlen, unsigned len)
> +static int smack_socket_getpeersec_stream(struct socket *sock, char **optval,
> + int *optlen, unsigned len)
> {
> - struct socket_smack *ssp;
> - char *rcp = "";
> - int slen = 1;
> + struct socket_smack *ssp = smack_sock(sock->sk);
> + char *rcp;
> + int slen;
> int rc = 0;
>
> - ssp = smack_sock(sock->sk);
> - if (ssp->smk_packet != NULL) {
> - rcp = ssp->smk_packet->smk_known;
> - slen = strlen(rcp) + 1;
> + if (ssp->smk_packet == NULL) {
> + *optlen = 0;
> + return -EINVAL;
> }
>
> + rcp = ssp->smk_packet->smk_known;
> + slen = strlen(rcp) + 1;
> if (slen > len)
> rc = -ERANGE;
> - else if (copy_to_user(optval, rcp, slen) != 0)
> - rc = -EFAULT;
> -
> - if (put_user(slen, optlen) != 0)
> - rc = -EFAULT;
> + else {
> + *optval = kstrdup(rcp, GFP_KERNEL);
> + if (*optval == NULL)
> + rc = -ENOMEM;
> + }
> + *optlen = slen;
>
> return rc;
> }
> --
> 2.20.1
>
--
Kees Cook
