Mercurial > dropbear
view dropbearkey.1 @ 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 | 5c8913b7464c |
| children |
line wrap: on
line source
.TH dropbearkey 1 .SH NAME dropbearkey \- create private keys for the use with dropbear(8) or dbclient(1) .SH SYNOPSIS .B dropbearkey \-t .I type \-f .I file [\-s .IR bits ] [\-y] .SH DESCRIPTION .B dropbearkey generates a \fIRSA\fR, \fIDSS\fR, \fIECDSA\fR, or \fIEd25519\fR format SSH private key, and saves it to a file for the use with the Dropbear client or server. Note that some SSH implementations use the term "DSA" rather than "DSS", they mean the same thing. .SH OPTIONS .TP .B \-t \fItype Type of key to generate. Must be one of .I rsa .I ecdsa .I ed25519 or .IR dss . .TP .B \-f \fIfile Write the secret key to the file \fIfile\fR. For client authentication ~/.ssh/id_dropbear is loaded by default .TP .B \-s \fIbits Set the key size to .I bits bits, should be multiple of 8 (optional). .TP .B \-y Just print the publickey and fingerprint for the private key in \fIfile\fR. .SH NOTES The program dropbearconvert(1) can be used to convert between Dropbear and OpenSSH key formats. .P Dropbear does not support encrypted keys. .SH EXAMPLE generate a host-key: # dropbearkey -t rsa -f /etc/dropbear/dropbear_rsa_host_key extract a public key suitable for authorized_keys from private key: # dropbearkey -y -f id_rsa | grep "^ssh-rsa " >> authorized_keys .SH AUTHOR Matt Johnston ([email protected]). .br Gerrit Pape ([email protected]) wrote this manual page. .SH SEE ALSO dropbear(8), dbclient(1), dropbearconvert(1) .P https://matt.ucc.asn.au/dropbear/dropbear.html