auth: introducing PAM account management for daemon by seks99x · Pull Request #1109 · RsyncProject/rsync

seks99x · 2026-09-29T13:09:44Z

This introduces PAM (Pluggable Authentication Modules) support specifically targeted at account management in the rsync daemon, alongside a structural refactor of the authentication codebase (#968) .

Following @tridge's architectural suggestions during the initial PAM discussions on discord, which was meant to be made firstly on the VFS branch , the authentication logic has been modularized into a dedicated subsystem. Created a new auth/ directory for authentication-related code, Moved authenticate.c to auth/authenticate.c, Introduced auth/pam.c and auth/auth.h to encapsulate the new PAM function (also supporting future changes) and cleanly expose prototypes.

PAM Account Management (pam_acct_mgmt):
To avoid transmitting credentials over the wire, this PAM integration is strictly limited to account management till now.
Implemented the use pam = yes configuration directive for rsyncd.conf which is off by default.
The daemon continues to use the standard MD5 challenge-response for cryptographic authentication. Once the MD5 hash is validated, the daemon calls pam_acct_mgmt() to ensure the underlying system account is active, valid, and not locked/expired before granting session access.

Testing & Coverage:
Expanded testsuite/daemon-auth_test.py to validate the new code paths across the daemon. Verified that non-existent system users (who pass the MD5 check but fail PAM validation) are safely rejected. Verified that real, active system users successfully pass both the MD5 and PAM management checks. I used Samba's pam_wrapper alongside a mock plugin (testsuite/pam/pam_mock.c). Used pkg-config to dynamically find the exact library path. If pam_wrapper or pkg-config is missing, or if running on macOS, the PAM tests are gracefully skipped.

I'm also trying to figure out an optimal way , which we could apply later or on this pr, that we could integrate PAM as an authentication method without changing a lot of the core protocol and transmitting the credentials safely.

This still needs some more work on the documentation, and maybe fixes for other stuff I missed or implemented incorrectly.

Co-authored-by: steadytao <mail@steadytao.com>

…configuraiton

steadytao · 2026-09-30T12:10:47Z

Do note that PAM should be opt-in during its initial rollout. Also, for those looking at this PR -- this feature will more or less allow PAM account-policy; at least for now.

steadytao · 2026-09-30T12:13:38Z

Ah I also don't need co-author on your commits. Primarily to ensure they're verified.

seks99x · 2026-09-30T14:45:01Z

I modified it to be as an optional argument of the compilation phase (./configure —enable-pam). The CI workflows will need to have pam_wrapper , pam (MacOS,solaris,netbsd,openbsd already do have pam only installed) and pkg-config installed. It also needs to be configured to compile with —enable-pam so it can actually run the PAM test case.
I’m also feeling its better to make the PAM test independent from the default auth so i can track well if any is really skipping/failing not gracefully skipping.

steadytao

Keep authenticate.c in place, document use pam in rsyncd.conf.5.md and add a CI job configured with --enable-pam (let me know if I will have to do that, I may) -- Ah. Do note to document it as account-policy verification rather than PAM auth.

steadytao · 2026-10-01T08:52:14Z

+static int rsync_pam_conv(int num_msg, PAM_MSG_CONST struct pam_message **msg,
+                          struct pam_response **resp, void *appdata_ptr)
+{
+    /* Suppress unused variable warnings */
+    (void)num_msg;
+    (void)msg;
+    (void)resp;
+    (void)appdata_ptr;
+
+    return PAM_CONV_ERR; 
+}


This rejects informational PAM messages. Accept PAM_TEXT_INFO and PAM_ERROR_MSG with empty responses and reject only interactive prompts.

steadytao · 2026-10-01T08:52:45Z

+		if (!err && use_pam) {
+			if (am_root != 1)


PAM does not universally require root. Call pam_acct_mgmt and let the application policy return permission errors.

steadytao · 2026-10-01T08:53:36Z

+        res = subprocess.run([pkg_config, "--libs", "pam_wrapper"], capture_output=True, text=True, check=True)
+        discovered_path = res.stdout.strip()
+        if os.path.exists(discovered_path):
+            pam_wrapper_so = discovered_path


pkg-config --libs returns linker flags rather than the path so this test normally skips. Resolve the actual shared object and add a PAM-enabled CI job which fails if the test skips -- let me know if you require me to do that, I think you might :D

pkg-config --libs return with the path not the flags on pam_wrapper.

pkg-config --libs pam_wrapper /usr/lib/x86_64-linux-gnu/libpam_wrapper.so

pam_wrapper packages can be installed like this

## pam_wrapper.pc modules=/usr/lib/x86_64-linux-gnu/pam_wrapper Name: pam_wrapper Description: The pam_wrapper library Version: 1.1.8 Libs: /usr/lib/x86_64-linux-gnu/libpam_wrapper.so

I initially tried using ctypes.util.find_library("pam_wrapper") but it didn't resolve properly, which is why I fell back to the pkg-config approach. Since .pc files can differ from machine to another, I'll push an update that dynamically handle two cases. If --libs returns an absolute path, it will use it; otherwise it will fallback to --variable=libdir to construct the correct path (which should be the standard).
Regarding CI I get an authorization error trying to modify anything under .github/workflows/, so I can't add it myself :(

steadytao · 2026-10-01T08:54:01Z

+#include <security/pam_appl.h>
+#include <security/pam_modules.h>


Configure accepts alternate PAM header layouts but this mock hard-codes the Linux paths. Use the configure results for both required headers.

steadytao · 2026-10-01T08:54:31Z

+proc = push(bad, target_module='pam_auth', user='tuser')
+if proc.returncode == 0 or "PAM: Account validation successful for user" in log_content:
+    test_fail("PAM module unexpectedly succeeded with the wrong password (fake user)")


log_content predates this request so the test does not prove PAM was skipped after a bad password. Reload the log or record mock invocation count.

seks99x · 2026-10-01T11:12:39Z

@steadytao do you mean you want a revert back and remove the auth/ dir? I'll append all in the authenticate.c , or do you prefer a pam.c / pam.h file?

steadytao · 2026-10-01T11:42:09Z

I only meant to keep authenticate.c in its existing location rather than moving the whole authentication subsystem. The current layout is fine. There is no need to move the PAM code again.

…subsystem

seks99x and others added 2 commits September 28, 2026 21:49

Introduce PAM account management integration for rsync daemon

170176d

Co-authored-by: steadytao <mail@steadytao.com>

Add a pam_mock.c for reliable PAM testing. Enhance the testsuite and …

695d2c2

…configuraiton

seks99x force-pushed the rsync-pam-management branch 9 times, most recently from 21e78d4 to 0e23ae7 Compare September 29, 2026 14:27

Fix solaris and macOS errors

3763d0d

seks99x force-pushed the rsync-pam-management branch from 0e23ae7 to 3763d0d Compare September 29, 2026 14:46

seks99x force-pushed the rsync-pam-management branch from 2adb892 to 647a83c Compare September 30, 2026 13:31

Let the pam optional check on configure.ac

6779d97

seks99x force-pushed the rsync-pam-management branch from 647a83c to 6779d97 Compare September 30, 2026 13:32

steadytao requested changes Oct 1, 2026

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seks99x force-pushed the rsync-pam-management branch 2 times, most recently from 6f90d08 to 8bf6af6 Compare October 1, 2026 11:40

Add PAM documentation to rsyncd.conf.5.md. Some tweaks. Remove auth/ …

e834eb6

…subsystem

seks99x force-pushed the rsync-pam-management branch from 8bf6af6 to e834eb6 Compare October 1, 2026 13:33

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auth: introducing PAM account management for daemon - #1109

auth: introducing PAM account management for daemon#1109
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		#include <security/pam_appl.h>
		#include <security/pam_modules.h>

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