File openssh-mitigate-lingering-secrets.patch of Package openssh
Index: openssh-9.3p2/kex.c
===================================================================
--- openssh-9.3p2.orig/kex.c
+++ openssh-9.3p2/kex.c
@@ -1564,16 +1564,16 @@ enc_destroy(struct sshenc *enc)
return;
if (enc->key) {
- memset(enc->key, 0, enc->key_len);
+ explicit_bzero(enc->key, enc->key_len);
free(enc->key);
}
if (enc->iv) {
- memset(enc->iv, 0, enc->iv_len);
+ explicit_bzero(enc->iv, enc->iv_len);
free(enc->iv);
}
- memset(enc, 0, sizeof(*enc));
+ explicit_bzero(enc, sizeof(*enc));
}
void
@@ -1584,7 +1584,7 @@ newkeys_destroy(struct newkeys *newkeys)
enc_destroy(&newkeys->enc);
mac_destroy(&newkeys->mac);
- memset(&newkeys->comp, 0, sizeof(newkeys->comp));
+ explicit_bzero(&newkeys->comp, sizeof(newkeys->comp));
}
/*
Index: openssh-9.3p2/mac.c
===================================================================
--- openssh-9.3p2.orig/mac.c
+++ openssh-9.3p2/mac.c
@@ -284,11 +284,11 @@ mac_destroy(struct sshmac *mac)
return;
if (mac->key) {
- memset(mac->key, 0, mac->key_len);
+ explicit_bzero(mac->key, mac->key_len);
free(mac->key);
}
- memset(mac, 0, sizeof(*mac));
+ explicit_bzero(mac, sizeof(*mac));
}
/* XXX copied from ciphers_valid */
Index: openssh-9.3p2/monitor.c
===================================================================
--- openssh-9.3p2.orig/monitor.c
+++ openssh-9.3p2/monitor.c
@@ -1789,8 +1789,12 @@ mm_answer_audit_end_command(struct ssh *
void
monitor_clear_keystate(struct ssh *ssh, struct monitor *pmonitor)
{
- ssh_clear_newkeys(ssh, MODE_IN);
- ssh_clear_newkeys(ssh, MODE_OUT);
+ u_int mode;
+
+ for (mode = 0; mode < MODE_MAX; mode++) {
+ ssh_clear_curkeys(ssh, mode); /* current keys */
+ ssh_clear_newkeys(ssh, mode); /* next keys */
+ }
sshbuf_free(child_state);
child_state = NULL;
}
Index: openssh-9.3p2/packet.c
===================================================================
--- openssh-9.3p2.orig/packet.c
+++ openssh-9.3p2/packet.c
@@ -655,6 +655,7 @@ ssh_packet_close_internal(struct ssh *ss
ssh->local_ipaddr = NULL;
free(ssh->remote_ipaddr);
ssh->remote_ipaddr = NULL;
+ explicit_bzero(ssh->state, sizeof(*ssh->state));
free(ssh->state);
ssh->state = NULL;
kex_free(ssh->kex);
@@ -783,8 +784,10 @@ compress_buffer(struct ssh *ssh, struct
case Z_OK:
/* Append compressed data to output_buffer. */
if ((r = sshbuf_put(out, buf, sizeof(buf) -
- ssh->state->compression_out_stream.avail_out)) != 0)
+ ssh->state->compression_out_stream.avail_out)) != 0) {
+ explicit_bzero(buf, sizeof(buf));
return r;
+ }
break;
case Z_STREAM_ERROR:
default:
@@ -819,8 +822,10 @@ uncompress_buffer(struct ssh *ssh, struc
switch (status) {
case Z_OK:
if ((r = sshbuf_put(out, buf, sizeof(buf) -
- ssh->state->compression_in_stream.avail_out)) != 0)
+ ssh->state->compression_in_stream.avail_out)) != 0) {
+ explicit_bzero(buf, sizeof(buf));
return r;
+ }
break;
case Z_BUF_ERROR:
/*
@@ -870,6 +875,17 @@ uncompress_buffer(struct ssh *ssh, struc
#endif /* WITH_ZLIB */
void
+ssh_clear_curkeys(struct ssh *ssh, int mode)
+{
+ struct session_state *state = ssh->state;
+
+ if (state && state->newkeys[mode]) {
+ kex_free_newkeys(state->newkeys[mode]);
+ state->newkeys[mode] = NULL;
+ }
+}
+
+void
ssh_clear_newkeys(struct ssh *ssh, int mode)
{
if (ssh->kex && ssh->kex->newkeys[mode]) {
@@ -1418,7 +1434,9 @@ ssh_packet_read_seqnr(struct ssh *ssh, u
}
/* Append it to the buffer. */
- if ((r = ssh_packet_process_incoming(ssh, buf, len)) != 0)
+ r = ssh_packet_process_incoming(ssh, buf, len);
+ explicit_bzero(buf, len);
+ if (r != 0)
goto out;
}
out:
@@ -2375,9 +2393,12 @@ ssh_packet_get_state(struct ssh *ssh, st
(r = sshbuf_put_u32(m, state->p_read.packets)) != 0 ||
(r = sshbuf_put_u64(m, state->p_read.bytes)) != 0 ||
(r = sshbuf_put_stringb(m, state->input)) != 0 ||
- (r = sshbuf_put_stringb(m, state->output)) != 0)
+ (r = sshbuf_put_stringb(m, state->output)) != 0) {
+ sshbuf_obfuscate(m);
return r;
+ }
+ sshbuf_obfuscate(m);
return 0;
}
@@ -2496,6 +2517,8 @@ ssh_packet_set_state(struct ssh *ssh, st
size_t ilen, olen;
int r;
+ sshbuf_unobfuscate(m);
+
if ((r = kex_from_blob(m, &ssh->kex)) != 0 ||
(r = newkeys_from_blob(m, ssh, MODE_OUT)) != 0 ||
(r = newkeys_from_blob(m, ssh, MODE_IN)) != 0 ||
@@ -2509,7 +2532,7 @@ ssh_packet_set_state(struct ssh *ssh, st
(r = sshbuf_get_u64(m, &state->p_read.blocks)) != 0 ||
(r = sshbuf_get_u32(m, &state->p_read.packets)) != 0 ||
(r = sshbuf_get_u64(m, &state->p_read.bytes)) != 0)
- return r;
+ goto out;
/*
* We set the time here so that in post-auth privsep child we
* count from the completion of the authentication.
@@ -2518,10 +2541,10 @@ ssh_packet_set_state(struct ssh *ssh, st
/* XXX ssh_set_newkeys overrides p_read.packets? XXX */
if ((r = ssh_set_newkeys(ssh, MODE_IN)) != 0 ||
(r = ssh_set_newkeys(ssh, MODE_OUT)) != 0)
- return r;
+ goto out;
if ((r = ssh_packet_set_postauth(ssh)) != 0)
- return r;
+ goto out;
sshbuf_reset(state->input);
sshbuf_reset(state->output);
@@ -2529,12 +2552,19 @@ ssh_packet_set_state(struct ssh *ssh, st
(r = sshbuf_get_string_direct(m, &output, &olen)) != 0 ||
(r = sshbuf_put(state->input, input, ilen)) != 0 ||
(r = sshbuf_put(state->output, output, olen)) != 0)
- return r;
+ goto out;
- if (sshbuf_len(m))
- return SSH_ERR_INVALID_FORMAT;
+ if (sshbuf_len(m)) {
+ r = SSH_ERR_INVALID_FORMAT;
+ goto out;
+ }
+
+ r = 0;
+out:
+ if (r != 0)
+ sshbuf_obfuscate(m);
debug3_f("done");
- return 0;
+ return r;
}
/* NEW API */
Index: openssh-9.3p2/packet.h
===================================================================
--- openssh-9.3p2.orig/packet.h
+++ openssh-9.3p2/packet.h
@@ -103,6 +103,7 @@ void ssh_packet_close(struct ssh *);
void ssh_packet_close(struct ssh *);
void ssh_packet_set_input_hook(struct ssh *, ssh_packet_hook_fn *, void *);
void ssh_packet_clear_keys(struct ssh *);
+void ssh_clear_curkeys(struct ssh *, int);
void ssh_clear_newkeys(struct ssh *, int);
int ssh_packet_is_rekeying(struct ssh *);
Index: openssh-9.3p2/sshbuf.c
===================================================================
--- openssh-9.3p2.orig/sshbuf.c
+++ openssh-9.3p2/sshbuf.c
@@ -309,6 +309,31 @@ sshbuf_mutable_ptr(const struct sshbuf *
return buf->d + buf->off;
}
+/* Trivially obfuscate the buffer. This is used to make sensitive data
+ * (e.g. keystate) slightly less obvious if found lingering in kernel
+ * memory after being sent from the privsep child to its parent.
+ *
+ * Longer term we should consider using a one-time pad or a stream cipher
+ * here. */
+void
+sshbuf_obfuscate(struct sshbuf *buf)
+{
+ size_t i;
+
+ if (sshbuf_check_sanity(buf) != 0 || buf->readonly || buf->refcount > 1)
+ return;
+
+ for (i = buf->off; i < buf->size; i++) {
+ buf->d [i] ^= 0xaa;
+ }
+}
+
+void
+sshbuf_unobfuscate(struct sshbuf *buf)
+{
+ sshbuf_obfuscate(buf);
+}
+
int
sshbuf_check_reserve(const struct sshbuf *buf, size_t len)
{
Index: openssh-9.3p2/sshbuf.h
===================================================================
--- openssh-9.3p2.orig/sshbuf.h
+++ openssh-9.3p2/sshbuf.h
@@ -298,6 +298,9 @@ int sshbuf_write_file(const char *path,
int sshbuf_read(int, struct sshbuf *, size_t, size_t *)
__attribute__((__nonnull__ (2)));
+void sshbuf_obfuscate(struct sshbuf *buf);
+void sshbuf_unobfuscate(struct sshbuf *buf);
+
/* Macros for decoding/encoding integers */
#define PEEK_U64(p) \
(((u_int64_t)(((const u_char *)(p))[0]) << 56) | \
Index: openssh-9.3p2/sshd-session.c
===================================================================
--- openssh-9.3p2.orig/sshd-session.c
+++ openssh-9.3p2/sshd-session.c
@@ -197,6 +197,19 @@ static void do_ssh2_kex(struct ssh *);
static void do_ssh2_kex(struct ssh *);
/*
+ * Clear some stack space. This is a bit naive, but hopefully helps mitigate
+ * information leaks due to registers and other data having been stored on
+ * the stack. Called after fork() and before exit().
+ */
+static void
+clobber_stack(void)
+{
+ char data [32768];
+
+ explicit_bzero(data, 32768);
+}
+
+/*
* Signal handler for the alarm after the login grace period has expired.
* As usual, this may only take signal-safe actions, even though it is
* terminal.
@@ -260,6 +260,8 @@ destroy_sensitive_data(struct ssh *ssh,
sensitive_data.host_certificates[i] = NULL;
}
}
+
+ clobber_stack();
}
/* Demote private to public keys for network child */
@@ -431,6 +432,8 @@ privsep_preauth(struct ssh *ssh)
{
int skip_privdrop = 0;
+ clobber_stack();
+
/*
* Hack for systems that don't support FD passing: retain privileges
* in the post-auth privsep process so it can allocate PTYs directly.
@@ -1354,6 +1356,7 @@ main(int ac, char **av)
*/
mm_send_keystate(ssh, pmonitor);
ssh_packet_clear_keys(ssh);
+ clobber_stack();
exit(0);
authenticated:
@@ -1431,6 +1434,7 @@ main(int ac, char **av)
mm_terminate();
+ clobber_stack();
exit(0);
}
@@ -1577,8 +1581,10 @@ cleanup_exit(int i)
/* cleanup_exit can be called at the very least from the privsep
wrappers used for auditing. Make sure we don't recurse
indefinitely. */
- if (in_cleanup)
+ if (in_cleanup) {
+ clobber_stack();
_exit(i);
+ }
in_cleanup = 1;
extern int auth_attempted; /* monitor.c */
@@ -1604,6 +1610,8 @@ cleanup_exit(int i)
mm_is_monitor())
audit_event(the_active_state, SSH_CONNECTION_ABANDON);
#endif
+
+ clobber_stack();
/* Override default fatal exit value when auth was attempted */
if (i == 255 && auth_attempted)
_exit(EXIT_AUTH_ATTEMPTED);
