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Systemd/src/journal/journald-context.c

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/***
This file is part of systemd.
Copyright 2017 Lennart Poettering
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
***/
#if HAVE_SELINUX
#include <selinux/selinux.h>
#endif
#include "alloc-util.h"
#include "audit-util.h"
#include "cgroup-util.h"
#include "journald-context.h"
#include "process-util.h"
#include "string-util.h"
#include "user-util.h"
/* This implements a metadata cache for clients, which are identified by their PID. Requesting metadata through /proc
* is expensive, hence let's cache the data if we can. Note that this means the metadata might be out-of-date when we
* store it, but it might already be anyway, as we request the data asynchronously from /proc at a different time the
* log entry was originally created. We hence just increase the "window of inaccuracy" a bit.
*
* The cache is indexed by the PID. Entries may be "pinned" in the cache, in which case the entries are not removed
* until they are unpinned. Unpinned entries are kept around until cache pressure is seen. Cache entries older than 5s
* are never used (a sad attempt to deal with the UNIX weakness of PIDs reuse), cache entries older than 1s are
* refreshed in an incremental way (meaning: data is reread from /proc, but any old data we can't refresh is not
* flushed out). Data newer than 1s is used immediately without refresh.
*
* Log stream clients (i.e. all clients using the AF_UNIX/SOCK_STREAM stdout/stderr transport) will pin a cache entry
* as long as their socket is connected. Note that cache entries are shared between different transports. That means a
* cache entry pinned for the stream connection logic may be reused for the syslog or native protocols.
*
* Caching metadata like this has two major benefits:
*
* 1. Reading metadata is expensive, and we can thus substantially speed up log processing under flood.
*
* 2. Because metadata caching is shared between stream and datagram transports and stream connections pin a cache
* entry there's a good chance we can properly map a substantial set of datagram log messages to their originating
* service, as all services (unless explicitly configured otherwise) will have their stdout/stderr connected to a
* stream connection. This should improve cases where a service process logs immediately before exiting and we
* previously had trouble associating the log message with the service.
*
* NB: With and without the metadata cache: the implicitly added entry metadata in the journal (with the exception of
* UID/PID/GID and SELinux label) must be understood as possibly slightly out of sync (i.e. sometimes slighly older
* and sometimes slightly newer than what was current at the log event).
*/
/* We refresh every 1s */
#define REFRESH_USEC (1*USEC_PER_SEC)
/* Data older than 5s we flush out */
#define MAX_USEC (5*USEC_PER_SEC)
/* Keep at most 16K entries in the cache. (Note though that this limit may be violated if enough streams pin entries in
* the cache, in which case we *do* permit this limit to be breached. That's safe however, as the number of stream
* clients itself is limited.) */
#define CACHE_MAX (16*1024)
static int client_context_compare(const void *a, const void *b) {
const ClientContext *x = a, *y = b;
if (x->timestamp < y->timestamp)
return -1;
if (x->timestamp > y->timestamp)
return 1;
if (x->pid < y->pid)
return -1;
if (x->pid > y->pid)
return 1;
return 0;
}
static int client_context_new(Server *s, pid_t pid, ClientContext **ret) {
ClientContext *c;
int r;
assert(s);
assert(pid_is_valid(pid));
assert(ret);
r = hashmap_ensure_allocated(&s->client_contexts, NULL);
if (r < 0)
return r;
r = prioq_ensure_allocated(&s->client_contexts_lru, client_context_compare);
if (r < 0)
return r;
c = new0(ClientContext, 1);
if (!c)
return -ENOMEM;
c->pid = pid;
c->uid = UID_INVALID;
c->gid = GID_INVALID;
c->auditid = AUDIT_SESSION_INVALID;
c->loginuid = UID_INVALID;
c->owner_uid = UID_INVALID;
c->lru_index = PRIOQ_IDX_NULL;
c->timestamp = USEC_INFINITY;
r = hashmap_put(s->client_contexts, PID_TO_PTR(pid), c);
if (r < 0) {
free(c);
return r;
}
*ret = c;
return 0;
}
static void client_context_reset(ClientContext *c) {
assert(c);
c->timestamp = USEC_INFINITY;
c->uid = UID_INVALID;
c->gid = GID_INVALID;
c->comm = mfree(c->comm);
c->exe = mfree(c->exe);
c->cmdline = mfree(c->cmdline);
c->capeff = mfree(c->capeff);
c->auditid = AUDIT_SESSION_INVALID;
c->loginuid = UID_INVALID;
c->cgroup = mfree(c->cgroup);
c->session = mfree(c->session);
c->owner_uid = UID_INVALID;
c->unit = mfree(c->unit);
c->user_unit = mfree(c->user_unit);
c->slice = mfree(c->slice);
c->user_slice = mfree(c->user_slice);
c->invocation_id = SD_ID128_NULL;
c->label = mfree(c->label);
c->label_size = 0;
}
static ClientContext* client_context_free(Server *s, ClientContext *c) {
assert(s);
if (!c)
return NULL;
assert_se(hashmap_remove(s->client_contexts, PID_TO_PTR(c->pid)) == c);
if (c->in_lru)
assert_se(prioq_remove(s->client_contexts_lru, c, &c->lru_index) >= 0);
client_context_reset(c);
return mfree(c);
}
static void client_context_read_uid_gid(ClientContext *c, const struct ucred *ucred) {
assert(c);
assert(pid_is_valid(c->pid));
/* The ucred data passed in is always the most current and accurate, if we have any. Use it. */
if (ucred && uid_is_valid(ucred->uid))
c->uid = ucred->uid;
else
(void) get_process_uid(c->pid, &c->uid);
if (ucred && gid_is_valid(ucred->gid))
c->gid = ucred->gid;
else
(void) get_process_gid(c->pid, &c->gid);
}
static void client_context_read_basic(ClientContext *c) {
char *t;
assert(c);
assert(pid_is_valid(c->pid));
if (get_process_comm(c->pid, &t) >= 0)
free_and_replace(c->comm, t);
if (get_process_exe(c->pid, &t) >= 0)
free_and_replace(c->exe, t);
if (get_process_cmdline(c->pid, 0, false, &t) >= 0)
free_and_replace(c->cmdline, t);
if (get_process_capeff(c->pid, &t) >= 0)
free_and_replace(c->capeff, t);
}
static int client_context_read_label(
ClientContext *c,
const char *label, size_t label_size) {
assert(c);
assert(pid_is_valid(c->pid));
assert(label_size == 0 || label);
if (label_size > 0) {
char *l;
/* If we got an SELinux label passed in it counts. */
l = newdup_suffix0(char, label, label_size);
if (!l)
return -ENOMEM;
free_and_replace(c->label, l);
c->label_size = label_size;
}
#if HAVE_SELINUX
else {
char *con;
/* If we got no SELinux label passed in, let's try to acquire one */
if (getpidcon(c->pid, &con) >= 0) {
free_and_replace(c->label, con);
c->label_size = strlen(c->label);
}
}
#endif
return 0;
}
static int client_context_read_cgroup(Server *s, ClientContext *c, const char *unit_id) {
char *t = NULL;
int r;
assert(c);
/* Try to acquire the current cgroup path */
r = cg_pid_get_path_shifted(c->pid, s->cgroup_root, &t);
if (r < 0) {
/* If that didn't work, we use the unit ID passed in as fallback, if we have nothing cached yet */
if (unit_id && !c->unit) {
c->unit = strdup(unit_id);
if (c->unit)
return 0;
}
return r;
}
/* Let's shortcut this if the cgroup path didn't change */
if (streq_ptr(c->cgroup, t)) {
free(t);
return 0;
}
free_and_replace(c->cgroup, t);
(void) cg_path_get_session(c->cgroup, &t);
free_and_replace(c->session, t);
if (cg_path_get_owner_uid(c->cgroup, &c->owner_uid) < 0)
c->owner_uid = UID_INVALID;
(void) cg_path_get_unit(c->cgroup, &t);
free_and_replace(c->unit, t);
(void) cg_path_get_user_unit(c->cgroup, &t);
free_and_replace(c->user_unit, t);
(void) cg_path_get_slice(c->cgroup, &t);
free_and_replace(c->slice, t);
(void) cg_path_get_user_slice(c->cgroup, &t);
free_and_replace(c->user_slice, t);
return 0;
}
static int client_context_read_invocation_id(
Server *s,
ClientContext *c) {
_cleanup_free_ char *escaped = NULL, *slice_path = NULL;
char ids[SD_ID128_STRING_MAX];
const char *p;
int r;
assert(s);
assert(c);
/* Read the invocation ID of a unit off a unit. It's stored in the "trusted.invocation_id" extended attribute
* on the cgroup path. */
if (!c->unit || !c->slice)
return 0;
r = cg_slice_to_path(c->slice, &slice_path);
if (r < 0)
return r;
escaped = cg_escape(c->unit);
if (!escaped)
return -ENOMEM;
p = strjoina(s->cgroup_root, "/", slice_path, "/", escaped);
if (!p)
return -ENOMEM;
r = cg_get_xattr(SYSTEMD_CGROUP_CONTROLLER, p, "trusted.invocation_id", ids, 32);
if (r < 0)
return r;
if (r != 32)
return -EINVAL;
ids[32] = 0;
return sd_id128_from_string(ids, &c->invocation_id);
}
static void client_context_really_refresh(
Server *s,
ClientContext *c,
const struct ucred *ucred,
const char *label, size_t label_size,
const char *unit_id,
usec_t timestamp) {
assert(s);
assert(c);
assert(pid_is_valid(c->pid));
if (timestamp == USEC_INFINITY)
timestamp = now(CLOCK_MONOTONIC);
client_context_read_uid_gid(c, ucred);
client_context_read_basic(c);
(void) client_context_read_label(c, label, label_size);
(void) audit_session_from_pid(c->pid, &c->auditid);
(void) audit_loginuid_from_pid(c->pid, &c->loginuid);
(void) client_context_read_cgroup(s, c, unit_id);
(void) client_context_read_invocation_id(s, c);
c->timestamp = timestamp;
if (c->in_lru) {
assert(c->n_ref == 0);
assert_se(prioq_reshuffle(s->client_contexts_lru, c, &c->lru_index) >= 0);
}
}
void client_context_maybe_refresh(
Server *s,
ClientContext *c,
const struct ucred *ucred,
const char *label, size_t label_size,
const char *unit_id,
usec_t timestamp) {
assert(s);
assert(c);
if (timestamp == USEC_INFINITY)
timestamp = now(CLOCK_MONOTONIC);
/* No cached data so far? Let's fill it up */
if (c->timestamp == USEC_INFINITY)
goto refresh;
/* If the data isn't pinned and if the cashed data is older than the upper limit, we flush it out
* entirely. This follows the logic that as long as an entry is pinned the PID reuse is unlikely. */
if (c->n_ref == 0 && c->timestamp + MAX_USEC < timestamp) {
client_context_reset(c);
goto refresh;
}
/* If the data is older than the lower limit, we refresh, but keep the old data for all we can't update */
if (c->timestamp + REFRESH_USEC < timestamp)
goto refresh;
/* If the data passed along doesn't match the cached data we also do a refresh */
if (ucred && uid_is_valid(ucred->uid) && c->uid != ucred->uid)
goto refresh;
if (ucred && gid_is_valid(ucred->gid) && c->gid != ucred->gid)
goto refresh;
if (label_size > 0 && (label_size != c->label_size || memcmp(label, c->label, label_size) != 0))
goto refresh;
return;
refresh:
client_context_really_refresh(s, c, ucred, label, label_size, unit_id, timestamp);
}
static void client_context_try_shrink_to(Server *s, size_t limit) {
assert(s);
/* Bring the number of cache entries below the indicated limit, so that we can create a new entry without
* breaching the limit. Note that we only flush out entries that aren't pinned here. This means the number of
* cache entries may very well grow beyond the limit, if all entries stored remain pinned. */
while (hashmap_size(s->client_contexts) > limit) {
ClientContext *c;
c = prioq_pop(s->client_contexts_lru);
if (!c)
break; /* All remaining entries are pinned, give up */
assert(c->in_lru);
assert(c->n_ref == 0);
c->in_lru = false;
client_context_free(s, c);
}
}
void client_context_flush_all(Server *s) {
assert(s);
/* Flush out all remaining entries. This assumes all references are already dropped. */
s->my_context = client_context_release(s, s->my_context);
s->pid1_context = client_context_release(s, s->pid1_context);
client_context_try_shrink_to(s, 0);
assert(prioq_size(s->client_contexts_lru) == 0);
assert(hashmap_size(s->client_contexts) == 0);
s->client_contexts_lru = prioq_free(s->client_contexts_lru);
s->client_contexts = hashmap_free(s->client_contexts);
}
static int client_context_get_internal(
Server *s,
pid_t pid,
const struct ucred *ucred,
const char *label, size_t label_len,
const char *unit_id,
bool add_ref,
ClientContext **ret) {
ClientContext *c;
int r;
assert(s);
assert(ret);
if (!pid_is_valid(pid))
return -EINVAL;
c = hashmap_get(s->client_contexts, PID_TO_PTR(pid));
if (c) {
if (add_ref) {
if (c->in_lru) {
/* The entry wasn't pinned so far, let's remove it from the LRU list then */
assert(c->n_ref == 0);
assert_se(prioq_remove(s->client_contexts_lru, c, &c->lru_index) >= 0);
c->in_lru = false;
}
c->n_ref++;
}
client_context_maybe_refresh(s, c, ucred, label, label_len, unit_id, USEC_INFINITY);
*ret = c;
return 0;
}
client_context_try_shrink_to(s, CACHE_MAX-1);
r = client_context_new(s, pid, &c);
if (r < 0)
return r;
if (add_ref)
c->n_ref++;
else {
r = prioq_put(s->client_contexts_lru, c, &c->lru_index);
if (r < 0) {
client_context_free(s, c);
return r;
}
c->in_lru = true;
}
client_context_really_refresh(s, c, ucred, label, label_len, unit_id, USEC_INFINITY);
*ret = c;
return 0;
}
int client_context_get(
Server *s,
pid_t pid,
const struct ucred *ucred,
const char *label, size_t label_len,
const char *unit_id,
ClientContext **ret) {
return client_context_get_internal(s, pid, ucred, label, label_len, unit_id, false, ret);
}
int client_context_acquire(
Server *s,
pid_t pid,
const struct ucred *ucred,
const char *label, size_t label_len,
const char *unit_id,
ClientContext **ret) {
return client_context_get_internal(s, pid, ucred, label, label_len, unit_id, true, ret);
};
ClientContext *client_context_release(Server *s, ClientContext *c) {
assert(s);
if (!c)
return NULL;
assert(c->n_ref > 0);
assert(!c->in_lru);
c->n_ref--;
if (c->n_ref > 0)
return NULL;
/* The entry is not pinned anymore, let's add it to the LRU prioq if we can. If we can't we'll drop it
* right-away */
if (prioq_put(s->client_contexts_lru, c, &c->lru_index) < 0)
client_context_free(s, c);
else
c->in_lru = true;
return NULL;
}
void client_context_acquire_default(Server *s) {
int r;
assert(s);
/* Ensure that our own and PID1's contexts are always pinned. Our own context is particularly useful to
* generate driver messages. */
if (!s->my_context) {
struct ucred ucred = {
.pid = getpid_cached(),
.uid = getuid(),
.gid = getgid(),
};
r = client_context_acquire(s, ucred.pid, &ucred, NULL, 0, NULL, &s->my_context);
if (r < 0)
log_warning_errno(r, "Failed to acquire our own context, ignoring: %m");
}
if (!s->pid1_context) {
r = client_context_acquire(s, 1, NULL, NULL, 0, NULL, &s->pid1_context);
if (r < 0)
log_warning_errno(r, "Failed to acquire PID1's context, ignoring: %m");
}
}
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