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logind: validate /run/user/1000 before we set it

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Let's be safe than sorry, in particular as logind doesn't set it up
anymore, but user-runtime-dir@.service does, and logind doesn't really
track success of that.
This commit is contained in:
Lennart Poettering 2018-10-09 22:23:41 +02:00
parent 93d4cb09d5
commit b921711248
1 changed files with 41 additions and 7 deletions
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48
src/login/pam_systemd.c
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@ -308,6 +308,36 @@ static int update_environment(pam_handle_t *handle, const char *key, const char
return r;
}
static bool validate_runtime_directory(pam_handle_t *handle, const char *path, uid_t uid) {
struct stat st;
assert(path);
/* Just some extra paranoia: let's not set $XDG_RUNTIME_DIR if the directory we'd set it to isn't actually set
* up properly for us. */
if (lstat(path, &st) < 0) {
pam_syslog(handle, LOG_ERR, "Failed to stat() runtime directory '%s': %s", path, strerror(errno));
goto fail;
}
if (!S_ISDIR(st.st_mode)) {
pam_syslog(handle, LOG_ERR, "Runtime directory '%s' is not actually a directory.", path);
goto fail;
}
if (st.st_uid != uid) {
pam_syslog(handle, LOG_ERR, "Runtime directory '%s' is not owned by UID " UID_FMT ", as it should.", path, uid);
goto fail;
}
return true;
fail:
pam_syslog(handle, LOG_WARNING, "Not setting $XDG_RUNTIME_DIR, as the directory is not in order.");
return false;
}
_public_ PAM_EXTERN int pam_sm_open_session(
pam_handle_t *handle,
int flags,
@ -367,10 +397,12 @@ _public_ PAM_EXTERN int pam_sm_open_session(
if (asprintf(&rt, "/run/user/"UID_FMT, pw->pw_uid) < 0)
return PAM_BUF_ERR;
r = pam_misc_setenv(handle, "XDG_RUNTIME_DIR", rt, 0);
if (r != PAM_SUCCESS) {
pam_syslog(handle, LOG_ERR, "Failed to set runtime dir.");
return r;
if (validate_runtime_directory(handle, rt, pw->pw_uid)) {
r = pam_misc_setenv(handle, "XDG_RUNTIME_DIR", rt, 0);
if (r != PAM_SUCCESS) {
pam_syslog(handle, LOG_ERR, "Failed to set runtime dir.");
return r;
}
}
return PAM_SUCCESS;
@ -574,9 +606,11 @@ _public_ PAM_EXTERN int pam_sm_open_session(
* in privileged apps clobbering the runtime directory
* unnecessarily. */
r = update_environment(handle, "XDG_RUNTIME_DIR", runtime_path);
if (r != PAM_SUCCESS)
return r;
if (validate_runtime_directory(handle, runtime_path, pw->pw_uid)) {
r = update_environment(handle, "XDG_RUNTIME_DIR", runtime_path);
if (r != PAM_SUCCESS)
return r;
}
}
/* Most likely we got the session/type/class from environment variables, but might have gotten the data