pam: make sure we don't assign colliding session ids if we get our session ids from multiple sources
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2e33c4331f
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2e225d657a
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@ -97,16 +97,30 @@ static int open_file_and_lock(const char *fn) {
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if ((fd = open(fn, O_RDWR|O_CLOEXEC|O_NOCTTY|O_NOFOLLOW|O_CREAT, 0600)) < 0)
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return -errno;
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/* The BSD socket semantics are a lot nicer than those of
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* POSIX locks. Which is why we use flock() here. BSD locking
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* does not work across NFS which however is not needed here
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* as the filesystems in question should be local, and only
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* locally accessible, and most likely even tmpfs. */
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if (flock(fd, LOCK_EX) < 0)
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return -errno;
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return fd;
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}
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static uint64_t get_session_id(void) {
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enum {
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SESSION_ID_AUDIT = 'a',
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SESSION_ID_COUNTER = 'c',
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SESSION_ID_RANDOM = 'r'
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};
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static uint64_t get_session_id(int *mode) {
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char *s;
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int fd;
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assert(mode);
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/* First attempt: let's use the session ID of the audit
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* system, if it is available. */
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if (read_one_line_file("/proc/self/sessionid", &s) >= 0) {
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@ -116,8 +130,10 @@ static uint64_t get_session_id(void) {
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r = safe_atou32(s, &u);
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free(s);
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if (r >= 0 && u != (uint32_t) -1)
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if (r >= 0 && u != (uint32_t) -1) {
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*mode = SESSION_ID_AUDIT;
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return (uint64_t) u;
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}
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}
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/* Second attempt, use our own counter. */
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@ -149,10 +165,14 @@ static uint64_t get_session_id(void) {
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close_nointr_nofail(fd);
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if (r >= 0)
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if (r >= 0) {
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*mode = SESSION_ID_COUNTER;
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return counter;
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}
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}
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*mode = SESSION_ID_RANDOM;
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/* Last attempt, pick a random value */
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return (uint64_t) random_ull();
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}
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@ -283,12 +303,21 @@ _public_ PAM_EXTERN int pam_sm_open_session(
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/* Reuse or create XDG session ID */
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if (!(id = pam_getenv(handle, "XDG_SESSION_ID"))) {
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int mode;
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if (asprintf(&buf, "%llu", (unsigned long long) get_session_id()) < 0) {
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if (asprintf(&buf, "%llux", (unsigned long long) get_session_id(&mode)) < 0) {
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r = PAM_BUF_ERR;
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goto finish;
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}
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/* To avoid id clashes we add the session id
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* source to our session ids. Note that the
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* session id source might change during
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* runtime, because a filesystem became
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* writable or the system reconfigured. */
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buf[strlen(buf)-1] =
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mode != SESSION_ID_AUDIT ? (char) mode : 0;
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if ((r = pam_misc_setenv(handle, "XDG_SESSION_ID", buf, 0)) != PAM_SUCCESS) {
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pam_syslog(handle, LOG_ERR, "Failed to set session id.");
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goto finish;
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