Mercurial > dropbear
view gensignkey.c @ 1788:1fc0012b9c38
Fix handling of replies to global requests (#112)
The current code assumes that all global requests want / need a reply.
This isn't always true and the request itself indicates if it wants a
reply or not.
It causes a specific problem with [email protected] messages.
These are sent by OpenSSH after authentication to inform the client of
potential other host keys for the host. This can be used to add a new
type of host key or to rotate host keys.
The initial information message from the server is sent as a global
request, but with want_reply set to false. This means that the server
doesn't expect an answer to this message. Instead the client needs to
send a prove request as a reply if it wants to receive proof of
ownership for the host keys.
The bug doesn't cause any current problems with due to how OpenSSH
treats receiving the failure message. It instead treats it as a
keepalive message and further ignores it.
Arguably this is a protocol violation though of Dropbear and it is only
accidental that it doesn't cause a problem with OpenSSH.
The bug was found when adding host keys support to libssh, which is more
strict protocol wise and treats the unexpected failure message an error,
also see https://gitlab.com/libssh/libssh-mirror/-/merge_requests/145
for more information.
The fix here is to honor the want_reply flag in the global request and
to only send a reply if the other side expects a reply.
author | Dirkjan Bussink <d.bussink@gmail.com> |
---|---|
date | Thu, 10 Dec 2020 16:13:13 +0100 |
parents | c795520269f9 |
children | 8b4274d34fe8 |
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#include "includes.h" #include "dbutil.h" #include "buffer.h" #include "ecdsa.h" #include "genrsa.h" #include "gendss.h" #include "gened25519.h" #include "signkey.h" #include "dbrandom.h" /* Returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */ static int buf_writefile(buffer * buf, const char * filename, int skip_exist) { int ret = DROPBEAR_FAILURE; int fd = -1; fd = open(filename, O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR); if (fd < 0) { /* If generating keys on connection (skip_exist) it's OK to get EEXIST - we probably just lost a race with another connection to generate the key */ if (skip_exist && errno == EEXIST) { ret = DROPBEAR_SUCCESS; } else { dropbear_log(LOG_ERR, "Couldn't create new file %s: %s", filename, strerror(errno)); } goto out; } /* write the file now */ while (buf->pos != buf->len) { int len = write(fd, buf_getptr(buf, buf->len - buf->pos), buf->len - buf->pos); if (len == -1 && errno == EINTR) { continue; } if (len <= 0) { dropbear_log(LOG_ERR, "Failed writing file %s: %s", filename, strerror(errno)); goto out; } buf_incrpos(buf, len); } ret = DROPBEAR_SUCCESS; out: if (fd >= 0) { if (fsync(fd) != 0) { dropbear_log(LOG_ERR, "fsync of %s failed: %s", filename, strerror(errno)); } m_close(fd); } return ret; } /* returns 0 on failure */ static int get_default_bits(enum signkey_type keytype) { switch (keytype) { #if DROPBEAR_RSA case DROPBEAR_SIGNKEY_RSA: return DROPBEAR_DEFAULT_RSA_SIZE; #endif #if DROPBEAR_DSS case DROPBEAR_SIGNKEY_DSS: /* DSS for SSH only defines 1024 bits */ return 1024; #endif #if DROPBEAR_ECDSA case DROPBEAR_SIGNKEY_ECDSA_KEYGEN: return ECDSA_DEFAULT_SIZE; case DROPBEAR_SIGNKEY_ECDSA_NISTP521: return 521; case DROPBEAR_SIGNKEY_ECDSA_NISTP384: return 384; case DROPBEAR_SIGNKEY_ECDSA_NISTP256: return 256; #endif #if DROPBEAR_ED25519 case DROPBEAR_SIGNKEY_ED25519: return 256; #endif default: return 0; } } int signkey_generate_get_bits(enum signkey_type keytype, int bits) { if (bits == 0) { bits = get_default_bits(keytype); } return bits; } /* if skip_exist is set it will silently return if the key file exists */ int signkey_generate(enum signkey_type keytype, int bits, const char* filename, int skip_exist) { sign_key * key = NULL; buffer *buf = NULL; char *fn_temp = NULL; int ret = DROPBEAR_FAILURE; bits = signkey_generate_get_bits(keytype, bits); /* now we can generate the key */ key = new_sign_key(); seedrandom(); switch(keytype) { #if DROPBEAR_RSA case DROPBEAR_SIGNKEY_RSA: key->rsakey = gen_rsa_priv_key(bits); break; #endif #if DROPBEAR_DSS case DROPBEAR_SIGNKEY_DSS: key->dsskey = gen_dss_priv_key(bits); break; #endif #if DROPBEAR_ECDSA case DROPBEAR_SIGNKEY_ECDSA_KEYGEN: case DROPBEAR_SIGNKEY_ECDSA_NISTP521: case DROPBEAR_SIGNKEY_ECDSA_NISTP384: case DROPBEAR_SIGNKEY_ECDSA_NISTP256: { ecc_key *ecckey = gen_ecdsa_priv_key(bits); keytype = ecdsa_signkey_type(ecckey); *signkey_key_ptr(key, keytype) = ecckey; } break; #endif #if DROPBEAR_ED25519 case DROPBEAR_SIGNKEY_ED25519: key->ed25519key = gen_ed25519_priv_key(bits); break; #endif default: dropbear_exit("Internal error"); } seedrandom(); buf = buf_new(MAX_PRIVKEY_SIZE); buf_put_priv_key(buf, key, keytype); sign_key_free(key); key = NULL; buf_setpos(buf, 0); fn_temp = m_malloc(strlen(filename) + 30); snprintf(fn_temp, strlen(filename)+30, "%s.tmp%d", filename, getpid()); ret = buf_writefile(buf, fn_temp, 0); if (ret == DROPBEAR_FAILURE) { goto out; } if (link(fn_temp, filename) < 0) { /* If generating keys on connection (skipexist) it's OK to get EEXIST - we probably just lost a race with another connection to generate the key */ if (!(skip_exist && errno == EEXIST)) { if (errno == EPERM || errno == EACCES) { /* Non-atomic fallback when hard-links not allowed or unsupported */ buf_setpos(buf, 0); ret = buf_writefile(buf, filename, skip_exist); } else { dropbear_log(LOG_ERR, "Failed moving key file to %s: %s", filename, strerror(errno)); ret = DROPBEAR_FAILURE; } goto out; } } /* ensure directory update is flushed to disk, otherwise we can end up with zero-byte hostkey files if the power goes off */ fsync_parent_dir(filename); out: if (buf) { buf_burn(buf); buf_free(buf); } if (fn_temp) { unlink(fn_temp); m_free(fn_temp); } return ret; }