Commit 2e225d65 authored by Lennart Poettering's avatar Lennart Poettering

pam: make sure we don't assign colliding session ids if we get our session ids...

pam: make sure we don't assign colliding session ids if we get our session ids from multiple sources
parent 2e33c433
......@@ -97,16 +97,30 @@ static int open_file_and_lock(const char *fn) {
if ((fd = open(fn, O_RDWR|O_CLOEXEC|O_NOCTTY|O_NOFOLLOW|O_CREAT, 0600)) < 0)
return -errno;
/* The BSD socket semantics are a lot nicer than those of
* POSIX locks. Which is why we use flock() here. BSD locking
* does not work across NFS which however is not needed here
* as the filesystems in question should be local, and only
* locally accessible, and most likely even tmpfs. */
if (flock(fd, LOCK_EX) < 0)
return -errno;
return fd;
}
static uint64_t get_session_id(void) {
enum {
SESSION_ID_AUDIT = 'a',
SESSION_ID_COUNTER = 'c',
SESSION_ID_RANDOM = 'r'
};
static uint64_t get_session_id(int *mode) {
char *s;
int fd;
assert(mode);
/* First attempt: let's use the session ID of the audit
* system, if it is available. */
if (read_one_line_file("/proc/self/sessionid", &s) >= 0) {
......@@ -116,8 +130,10 @@ static uint64_t get_session_id(void) {
r = safe_atou32(s, &u);
free(s);
if (r >= 0 && u != (uint32_t) -1)
if (r >= 0 && u != (uint32_t) -1) {
*mode = SESSION_ID_AUDIT;
return (uint64_t) u;
}
}
/* Second attempt, use our own counter. */
......@@ -149,10 +165,14 @@ static uint64_t get_session_id(void) {
close_nointr_nofail(fd);
if (r >= 0)
if (r >= 0) {
*mode = SESSION_ID_COUNTER;
return counter;
}
}
*mode = SESSION_ID_RANDOM;
/* Last attempt, pick a random value */
return (uint64_t) random_ull();
}
......@@ -283,12 +303,21 @@ _public_ PAM_EXTERN int pam_sm_open_session(
/* Reuse or create XDG session ID */
if (!(id = pam_getenv(handle, "XDG_SESSION_ID"))) {
int mode;
if (asprintf(&buf, "%llu", (unsigned long long) get_session_id()) < 0) {
if (asprintf(&buf, "%llux", (unsigned long long) get_session_id(&mode)) < 0) {
r = PAM_BUF_ERR;
goto finish;
}
/* To avoid id clashes we add the session id
* source to our session ids. Note that the
* session id source might change during
* runtime, because a filesystem became
* writable or the system reconfigured. */
buf[strlen(buf)-1] =
mode != SESSION_ID_AUDIT ? (char) mode : 0;
if ((r = pam_misc_setenv(handle, "XDG_SESSION_ID", buf, 0)) != PAM_SUCCESS) {
pam_syslog(handle, LOG_ERR, "Failed to set session id.");
goto finish;
......
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