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userauth: fix replacement of embedded with detached RSA cert.

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If you specify a detached certificate, it's supposed to completely
replace any certificate that might have been embedded in the input PPK
file. But one thing wasn't working: if the key was RSA, and the server
was using new SHA-2 based RSA, and the user provided both an embedded
_and_ detached certificate, then the initial call to
ssh2_userauth_signflags would upgrade the ssh-rsa-cert-... key type to
rsa-sha2-NNN-cert-..., which ssh2_userauth_add_alg_and_publickey's
call to ssh_keyalg_related_alg would not recognise as any of the base
RSA types while trying to decide on the key algorithm string _after_
replacing the certificate.

Fixed by reverting to the the uncertified base algorithm before
calling ssh_keyalg_related_alg.
This commit is contained in:
Simon Tatham 2023-05-04 17:59:37 +01:00
parent 70aabdc67c
commit cfe6fd95a7
1 changed files with 12 additions and 1 deletions
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13
ssh/userauth2-client.c
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@ -2373,7 +2373,18 @@ static void ssh2_userauth_add_alg_and_publickey(
ppl_logevent("Sending public key with certificate from \"%s\"",
filename_to_str(s->detached_cert_file));
}
put_stringz(pkt, ssh_keyalg_related_alg(certalg, pkalg)->ssh_id);
{
/* Strip off any existing certificate-nature from pkalg,
* for the case where we're replacing a cert embedded in
* the key with the detached one. The second argument of
* ssh_keyalg_related_alg is expected to be one of the
* bare key algorithms, or nothing useful will happen. */
const ssh_keyalg *pkalg_base =
pkalg->base_alg ? pkalg->base_alg : pkalg;
const ssh_keyalg *output_alg =
ssh_keyalg_related_alg(certalg, pkalg_base);
put_stringz(pkt, output_alg->ssh_id);
}
put_stringpl(pkt, ptrlen_from_strbuf(s->detached_cert_blob));
done = true;
goto out;