microsoft/azure: allow empty certificate chain in PKCS12 file

docs/release-notes.md

@@ -13,6 +13,7 @@ Major changes:
 Minor changes:
 
 - Hetzner: fix duplicate attribute prefix
+- Fix Azure SSH key fetching when no key provisioned
 
 Packaging changes:
 

src/providers/microsoft/azure/mod.rs

@@ -251,7 +251,7 @@ impl Azure {
     }
 
     // put it all together
-    fn get_ssh_pubkey(&self, certs_endpoint: String) -> Result<PublicKey> {
+    fn get_ssh_pubkey(&self, certs_endpoint: String) -> Result<Option<PublicKey>> {
         // we have to generate the rsa public/private keypair and the x509 cert
         // that we use to make the request. this is equivalent to
         // `openssl req -x509 -nodes -subj /CN=LinuxTransport -days 365 -newkey rsa:2048 -keyout private.pem -out cert.pem`
@@ -271,10 +271,7 @@ impl Azure {
             .context("failed to decrypt cms blob")?;
 
         // convert that to the OpenSSH public key format
-        let ssh_pubkey = crypto::p12_to_ssh_pubkey(&p12)
-            .context("failed to convert pkcs12 blob to ssh pubkey")?;
-
-        Ok(ssh_pubkey)
+        crypto::p12_to_ssh_pubkey(&p12).context("failed to convert pkcs12 blob to ssh pubkey")
     }
 
     #[cfg(test)]
@@ -402,18 +399,17 @@ impl MetadataProvider for Azure {
         let goalstate = self.fetch_goalstate()?;
         let certs_endpoint = match goalstate.certs_endpoint() {
             Some(ep) => ep,
-            None => {
-                warn!("SSH pubkeys requested, but not provisioned for this instance");
-                return Ok(vec![]);
-            }
+            None => return Ok(vec![]),
         };
 
         if certs_endpoint.is_empty() {
             bail!("unexpected empty certificates endpoint");
         }
 
-        let key = self.get_ssh_pubkey(certs_endpoint)?;
-        Ok(vec![key])
+        let maybe_key = self.get_ssh_pubkey(certs_endpoint)?;
+        let key: Vec<PublicKey> = maybe_key.into_iter().collect();
+
+        Ok(key)
     }
 
     fn boot_checkin(&self) -> Result<()> {

src/providers/microsoft/azurestack/mod.rs

@@ -267,7 +267,7 @@ impl AzureStack {
     }
 
     // put it all together
-    fn get_ssh_pubkey(&self, certs_endpoint: String) -> Result<PublicKey> {
+    fn get_ssh_pubkey(&self, certs_endpoint: String) -> Result<Option<PublicKey>> {
         // we have to generate the rsa public/private keypair and the x509 cert
         // that we use to make the request. this is equivalent to
         // `openssl req -x509 -nodes -subj /CN=LinuxTransport -days 365 -newkey rsa:2048 -keyout private.pem -out cert.pem`
@@ -287,10 +287,7 @@ impl AzureStack {
             .context("failed to decrypt cms blob")?;
 
         // convert that to the OpenSSH public key format
-        let ssh_pubkey = crypto::p12_to_ssh_pubkey(&p12)
-            .context("failed to convert pkcs12 blob to ssh pubkey")?;
-
-        Ok(ssh_pubkey)
+        crypto::p12_to_ssh_pubkey(&p12).context("failed to convert pkcs12 blob to ssh pubkey")
     }
 
     fn fetch_hostname(&self) -> Result<Option<String>> {
@@ -326,18 +323,17 @@ impl MetadataProvider for AzureStack {
         let goalstate = self.fetch_goalstate()?;
         let certs_endpoint = match goalstate.certs_endpoint() {
             Some(ep) => ep,
-            None => {
-                warn!("SSH pubkeys requested, but not provisioned for this instance");
-                return Ok(vec![]);
-            }
+            None => return Ok(vec![]),
         };
 
         if certs_endpoint.is_empty() {
             bail!("unexpected empty certificates endpoint");
         }
 
-        let key = self.get_ssh_pubkey(certs_endpoint)?;
-        Ok(vec![key])
+        let maybe_key = self.get_ssh_pubkey(certs_endpoint)?;
+        let key: Vec<PublicKey> = maybe_key.into_iter().collect();
+
+        Ok(key)
     }
 
     fn boot_checkin(&self) -> Result<()> {

src/providers/microsoft/crypto/mod.rs

@@ -54,7 +54,7 @@ pub fn decrypt_cms(smime: &[u8], pkey: &PKey<Private>, x509: &X509) -> Result<Ve
     Ok(p12_der)
 }
 
-pub fn p12_to_ssh_pubkey(p12_der: &[u8]) -> Result<PublicKey> {
+pub fn p12_to_ssh_pubkey(p12_der: &[u8]) -> Result<Option<PublicKey>> {
     // the contents of that encrypted cms blob we got are actually a different
     // cryptographic structure. we read that in from the contents and parse it.
     // PKCS12 has the ability to have a password, but we don't have one, hence
@@ -65,7 +65,14 @@ pub fn p12_to_ssh_pubkey(p12_der: &[u8]) -> Result<PublicKey> {
     // ParsedPKCS12_2 has three parts: a pkey, a main x509 cert, and a list of other
     // x509 certs. The list of other x509 certs are called the `certificate chain`
     // currently denoted as `ca`; there is only one cert in this `certificate chain`,
-    // which is the ssh public key.
+    // which is the ssh public key. The certs endpoint may still be populated even if
+    // an SSH public key hasn't been provided, which would lead to this code being
+    // executed. The certificate chain will be empty in this case, so just return
+    // None and handle it further up the stack.
+    if p12.ca.is_none() {
+        return Ok(None);
+    }
+
     let ca = p12
         .ca
         .ok_or_else(|| anyhow!("failed to get chain from pkcs12"))?;
@@ -86,5 +93,5 @@ pub fn p12_to_ssh_pubkey(p12_der: &[u8]) -> Result<PublicKey> {
     let n = ssh_pubkey_rsa.n().to_vec();
     let ssh_pubkey = PublicKey::from_rsa(e, n);
 
-    Ok(ssh_pubkey)
+    Ok(Some(ssh_pubkey))
 }