Fix bug #81026 (PHP-FPM oob R/W in root process leading to priv escal…

…ation)

The main change is to store scoreboard procs directly to the variable sized
array rather than indirectly through the pointer.

Signed-off-by: Stanislav Malyshev <stas@php.net>
(cherry picked from commit cb2021e)

Closes GH-7614.

NEWS

@@ -1,8 +1,14 @@
 PHP                                                                        NEWS
 |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
-?? ??? ????, PHP 7.3.32
+?? ??? ????, PHP 7.3.33
 
 
+28 Okt 2021, PHP 7.3.32
+
+- FPM:
+  . Fixed bug #81026 (PHP-FPM oob R/W in root process leading to privilege
+    escalation). (CVE-2021-21703) (Jakub Zelenka)
+
 23 Sep 2021, PHP 7.3.31
 
 - Zip:

sapi/fpm/fpm/fpm_children.c

@@ -246,7 +246,7 @@ void fpm_children_bury() /* {{{ */
 
 			fpm_child_unlink(child);
 
-			fpm_scoreboard_proc_free(wp->scoreboard, child->scoreboard_i);
+			fpm_scoreboard_proc_free(child);
 
 			fpm_clock_get(&tv1);
 
@@ -256,9 +256,9 @@ void fpm_children_bury() /* {{{ */
 				if (!fpm_pctl_can_spawn_children()) {
 					severity = ZLOG_DEBUG;
 				}
-				zlog(severity, "[pool %s] child %d exited %s after %ld.%06d seconds from start", child->wp->config->name, (int) pid, buf, tv2.tv_sec, (int) tv2.tv_usec);
+				zlog(severity, "[pool %s] child %d exited %s after %ld.%06d seconds from start", wp->config->name, (int) pid, buf, tv2.tv_sec, (int) tv2.tv_usec);
 			} else {
-				zlog(ZLOG_DEBUG, "[pool %s] child %d has been killed by the process management after %ld.%06d seconds from start", child->wp->config->name, (int) pid, tv2.tv_sec, (int) tv2.tv_usec);
+				zlog(ZLOG_DEBUG, "[pool %s] child %d has been killed by the process management after %ld.%06d seconds from start", wp->config->name, (int) pid, tv2.tv_sec, (int) tv2.tv_usec);
 			}
 
 			fpm_child_close(child, 1 /* in event_loop */);
@@ -324,7 +324,7 @@ static struct fpm_child_s *fpm_resources_prepare(struct fpm_worker_pool_s *wp) /
 		return 0;
 	}
 
-	if (0 > fpm_scoreboard_proc_alloc(wp->scoreboard, &c->scoreboard_i)) {
+	if (0 > fpm_scoreboard_proc_alloc(c)) {
 		fpm_stdio_discard_pipes(c);
 		fpm_child_free(c);
 		return 0;
@@ -336,7 +336,7 @@ static struct fpm_child_s *fpm_resources_prepare(struct fpm_worker_pool_s *wp) /
 
 static void fpm_resources_discard(struct fpm_child_s *child) /* {{{ */
 {
-	fpm_scoreboard_proc_free(child->wp->scoreboard, child->scoreboard_i);
+	fpm_scoreboard_proc_free(child);
 	fpm_stdio_discard_pipes(child);
 	fpm_child_free(child);
 }
@@ -349,10 +349,10 @@ static void fpm_child_resources_use(struct fpm_child_s *child) /* {{{ */
 		if (wp == child->wp) {
 			continue;
 		}
-		fpm_scoreboard_free(wp->scoreboard);
+		fpm_scoreboard_free(wp);
 	}
 
-	fpm_scoreboard_child_use(child->wp->scoreboard, child->scoreboard_i, getpid());
+	fpm_scoreboard_child_use(child, getpid());
 	fpm_stdio_child_use_pipes(child);
 	fpm_child_free(child);
 }

sapi/fpm/fpm/fpm_request.c

@@ -287,7 +287,7 @@ int fpm_request_is_idle(struct fpm_child_s *child) /* {{{ */
 	struct fpm_scoreboard_proc_s *proc;
 
 	/* no need in atomicity here */
-	proc = fpm_scoreboard_proc_get(child->wp->scoreboard, child->scoreboard_i);
+	proc = fpm_scoreboard_proc_get_from_child(child);
 	if (!proc) {
 		return 0;
 	}
@@ -302,7 +302,7 @@ int fpm_request_last_activity(struct fpm_child_s *child, struct timeval *tv) /*
 
 	if (!tv) return -1;
 
-	proc = fpm_scoreboard_proc_get(child->wp->scoreboard, child->scoreboard_i);
+	proc = fpm_scoreboard_proc_get_from_child(child);
 	if (!proc) {
 		return -1;
 	}

sapi/fpm/fpm/fpm_scoreboard.c

@@ -6,6 +6,7 @@
 #include <time.h>
 
 #include "fpm_config.h"
+#include "fpm_children.h"
 #include "fpm_scoreboard.h"
 #include "fpm_shm.h"
 #include "fpm_sockets.h"
@@ -23,7 +24,6 @@ static float fpm_scoreboard_tick;
 int fpm_scoreboard_init_main() /* {{{ */
 {
 	struct fpm_worker_pool_s *wp;
-	unsigned int i;
 
 #ifdef HAVE_TIMES
 #if (defined(HAVE_SYSCONF) && defined(_SC_CLK_TCK))
@@ -40,7 +40,7 @@ int fpm_scoreboard_init_main() /* {{{ */
 
 
 	for (wp = fpm_worker_all_pools; wp; wp = wp->next) {
-		size_t scoreboard_size, scoreboard_nprocs_size;
+		size_t scoreboard_procs_size;
 		void *shm_mem;
 
 		if (wp->config->pm_max_children < 1) {
@@ -53,22 +53,15 @@ int fpm_scoreboard_init_main() /* {{{ */
 			return -1;
 		}
 
-		scoreboard_size        = sizeof(struct fpm_scoreboard_s) + (wp->config->pm_max_children) * sizeof(struct fpm_scoreboard_proc_s *);
-		scoreboard_nprocs_size = sizeof(struct fpm_scoreboard_proc_s) * wp->config->pm_max_children;
-		shm_mem                = fpm_shm_alloc(scoreboard_size + scoreboard_nprocs_size);
+		scoreboard_procs_size = sizeof(struct fpm_scoreboard_proc_s) * wp->config->pm_max_children;
+		shm_mem = fpm_shm_alloc(sizeof(struct fpm_scoreboard_s) + scoreboard_procs_size);
 
 		if (!shm_mem) {
 			return -1;
 		}
-		wp->scoreboard         = shm_mem;
+		wp->scoreboard = shm_mem;
+		wp->scoreboard->pm = wp->config->pm;
 		wp->scoreboard->nprocs = wp->config->pm_max_children;
-		shm_mem               += scoreboard_size;
-
-		for (i = 0; i < wp->scoreboard->nprocs; i++, shm_mem += sizeof(struct fpm_scoreboard_proc_s)) {
-			wp->scoreboard->procs[i] = shm_mem;
-		}
-
-		wp->scoreboard->pm          = wp->config->pm;
 		wp->scoreboard->start_epoch = time(NULL);
 		strlcpy(wp->scoreboard->pool, wp->config->name, sizeof(wp->scoreboard->pool));
 	}
@@ -162,28 +155,48 @@ struct fpm_scoreboard_s *fpm_scoreboard_get() /* {{{*/
 }
 /* }}} */
 
-struct fpm_scoreboard_proc_s *fpm_scoreboard_proc_get(struct fpm_scoreboard_s *scoreboard, int child_index) /* {{{*/
+static inline struct fpm_scoreboard_proc_s *fpm_scoreboard_proc_get_ex(
+		struct fpm_scoreboard_s *scoreboard, int child_index, unsigned int nprocs) /* {{{*/
 {
 	if (!scoreboard) {
-		scoreboard = fpm_scoreboard;
+		return NULL;
 	}
 
-	if (!scoreboard) {
+	if (child_index < 0 || (unsigned int)child_index >= nprocs) {
 		return NULL;
 	}
 
+	return &scoreboard->procs[child_index];
+}
+/* }}} */
+
+struct fpm_scoreboard_proc_s *fpm_scoreboard_proc_get(
+		struct fpm_scoreboard_s *scoreboard, int child_index) /* {{{*/
+{
+	if (!scoreboard) {
+		scoreboard = fpm_scoreboard;
+	}
+
 	if (child_index < 0) {
 		child_index = fpm_scoreboard_i;
 	}
 
-	if (child_index < 0 || (unsigned int)child_index >= scoreboard->nprocs) {
-		return NULL;
-	}
+	return fpm_scoreboard_proc_get_ex(scoreboard, child_index, scoreboard->nprocs);
+}
+/* }}} */
 
-	return scoreboard->procs[child_index];
+struct fpm_scoreboard_proc_s *fpm_scoreboard_proc_get_from_child(struct fpm_child_s *child) /* {{{*/
+{
+	struct fpm_worker_pool_s *wp = child->wp;
+	unsigned int nprocs = wp->config->pm_max_children;
+	struct fpm_scoreboard_s *scoreboard = wp->scoreboard;
+	int child_index = child->scoreboard_i;
+
+	return fpm_scoreboard_proc_get_ex(scoreboard, child_index, nprocs);
 }
 /* }}} */
 
+
 struct fpm_scoreboard_s *fpm_scoreboard_acquire(struct fpm_scoreboard_s *scoreboard, int nohang) /* {{{ */
 {
 	struct fpm_scoreboard_s *s;
@@ -234,28 +247,28 @@ void fpm_scoreboard_proc_release(struct fpm_scoreboard_proc_s *proc) /* {{{ */
 	proc->lock = 0;
 }
 
-void fpm_scoreboard_free(struct fpm_scoreboard_s *scoreboard) /* {{{ */
+void fpm_scoreboard_free(struct fpm_worker_pool_s *wp) /* {{{ */
 {
-	size_t scoreboard_size, scoreboard_nprocs_size;
+	size_t scoreboard_procs_size;
+	struct fpm_scoreboard_s *scoreboard = wp->scoreboard;
 
 	if (!scoreboard) {
 		zlog(ZLOG_ERROR, "**scoreboard is NULL");
 		return;
 	}
 
-	scoreboard_size        = sizeof(struct fpm_scoreboard_s) + (scoreboard->nprocs) * sizeof(struct fpm_scoreboard_proc_s *);
-	scoreboard_nprocs_size = sizeof(struct fpm_scoreboard_proc_s) * scoreboard->nprocs;
+	scoreboard_procs_size = sizeof(struct fpm_scoreboard_proc_s) * wp->config->pm_max_children;
 
-	fpm_shm_free(scoreboard, scoreboard_size + scoreboard_nprocs_size);
+	fpm_shm_free(scoreboard, sizeof(struct fpm_scoreboard_s) + scoreboard_procs_size);
 }
 /* }}} */
 
-void fpm_scoreboard_child_use(struct fpm_scoreboard_s *scoreboard, int child_index, pid_t pid) /* {{{ */
+void fpm_scoreboard_child_use(struct fpm_child_s *child, pid_t pid) /* {{{ */
 {
 	struct fpm_scoreboard_proc_s *proc;
-	fpm_scoreboard = scoreboard;
-	fpm_scoreboard_i = child_index;
-	proc = fpm_scoreboard_proc_get(scoreboard, child_index);
+	fpm_scoreboard = child->wp->scoreboard;
+	fpm_scoreboard_i = child->scoreboard_i;
+	proc = fpm_scoreboard_proc_get_from_child(child);
 	if (!proc) {
 		return;
 	}
@@ -264,60 +277,67 @@ void fpm_scoreboard_child_use(struct fpm_scoreboard_s *scoreboard, int child_ind
 }
 /* }}} */
 
-void fpm_scoreboard_proc_free(struct fpm_scoreboard_s *scoreboard, int child_index) /* {{{ */
+void fpm_scoreboard_proc_free(struct fpm_child_s *child) /* {{{ */
 {
+	struct fpm_worker_pool_s *wp = child->wp;
+	struct fpm_scoreboard_s *scoreboard = wp->scoreboard;
+	int child_index = child->scoreboard_i;
+
 	if (!scoreboard) {
 		return;
 	}
 
-	if (child_index < 0 || (unsigned int)child_index >= scoreboard->nprocs) {
+	if (child_index < 0 || child_index >= wp->config->pm_max_children) {
 		return;
 	}
 
-	if (scoreboard->procs[child_index] && scoreboard->procs[child_index]->used > 0) {
-		memset(scoreboard->procs[child_index], 0, sizeof(struct fpm_scoreboard_proc_s));
+	if (scoreboard->procs[child_index].used > 0) {
+		memset(&scoreboard->procs[child_index], 0, sizeof(struct fpm_scoreboard_proc_s));
 	}
 
 	/* set this slot as free to avoid search on next alloc */
 	scoreboard->free_proc = child_index;
 }
 /* }}} */
 
-int fpm_scoreboard_proc_alloc(struct fpm_scoreboard_s *scoreboard, int *child_index) /* {{{ */
+int fpm_scoreboard_proc_alloc(struct fpm_child_s *child) /* {{{ */
 {
 	int i = -1;
+	struct fpm_worker_pool_s *wp = child->wp;
+	struct fpm_scoreboard_s *scoreboard = wp->scoreboard;
+	int nprocs = wp->config->pm_max_children;
 
-	if (!scoreboard || !child_index) {
+	if (!scoreboard) {
 		return -1;
 	}
 
 	/* first try the slot which is supposed to be free */
-	if (scoreboard->free_proc >= 0 && (unsigned int)scoreboard->free_proc < scoreboard->nprocs) {
-		if (scoreboard->procs[scoreboard->free_proc] && !scoreboard->procs[scoreboard->free_proc]->used) {
+	if (scoreboard->free_proc >= 0 && scoreboard->free_proc < nprocs) {
+		if (!scoreboard->procs[scoreboard->free_proc].used) {
 			i = scoreboard->free_proc;
 		}
 	}
 
 	if (i < 0) { /* the supposed free slot is not, let's search for a free slot */
 		zlog(ZLOG_DEBUG, "[pool %s] the proc->free_slot was not free. Let's search", scoreboard->pool);
-		for (i = 0; i < (int)scoreboard->nprocs; i++) {
-			if (scoreboard->procs[i] && !scoreboard->procs[i]->used) { /* found */
+		for (i = 0; i < nprocs; i++) {
+			if (!scoreboard->procs[i].used) { /* found */
 				break;
 			}
 		}
 	}
 
 	/* no free slot */
-	if (i < 0 || i >= (int)scoreboard->nprocs) {
+	if (i < 0 || i >= nprocs) {
 		zlog(ZLOG_ERROR, "[pool %s] no free scoreboard slot", scoreboard->pool);
 		return -1;
 	}
 
-	scoreboard->procs[i]->used = 1;
-	*child_index = i;
+	scoreboard->procs[i].used = 1;
+	child->scoreboard_i = i;
 
 	/* supposed next slot is free */
-	if (i + 1 >= (int)scoreboard->nprocs) {
+	if (i + 1 >= nprocs) {
 		scoreboard->free_proc = 0;
 	} else {
 		scoreboard->free_proc = i + 1;

sapi/fpm/fpm/fpm_scoreboard.h

@@ -63,7 +63,7 @@ struct fpm_scoreboard_s {
 	unsigned int nprocs;
 	int free_proc;
 	unsigned long int slow_rq;
-	struct fpm_scoreboard_proc_s *procs[];
+	struct fpm_scoreboard_proc_s procs[];
 };
 
 int fpm_scoreboard_init_main();
@@ -72,18 +72,19 @@ int fpm_scoreboard_init_child(struct fpm_worker_pool_s *wp);
 void fpm_scoreboard_update(int idle, int active, int lq, int lq_len, int requests, int max_children_reached, int slow_rq, int action, struct fpm_scoreboard_s *scoreboard);
 struct fpm_scoreboard_s *fpm_scoreboard_get();
 struct fpm_scoreboard_proc_s *fpm_scoreboard_proc_get(struct fpm_scoreboard_s *scoreboard, int child_index);
+struct fpm_scoreboard_proc_s *fpm_scoreboard_proc_get_from_child(struct fpm_child_s *child);
 
 struct fpm_scoreboard_s *fpm_scoreboard_acquire(struct fpm_scoreboard_s *scoreboard, int nohang);
 void fpm_scoreboard_release(struct fpm_scoreboard_s *scoreboard);
 struct fpm_scoreboard_proc_s *fpm_scoreboard_proc_acquire(struct fpm_scoreboard_s *scoreboard, int child_index, int nohang);
 void fpm_scoreboard_proc_release(struct fpm_scoreboard_proc_s *proc);
 
-void fpm_scoreboard_free(struct fpm_scoreboard_s *scoreboard);
+void fpm_scoreboard_free(struct fpm_worker_pool_s *wp);
 
-void fpm_scoreboard_child_use(struct fpm_scoreboard_s *scoreboard, int child_index, pid_t pid);
+void fpm_scoreboard_child_use(struct fpm_child_s *child, pid_t pid);
 
-void fpm_scoreboard_proc_free(struct fpm_scoreboard_s *scoreboard, int child_index);
-int fpm_scoreboard_proc_alloc(struct fpm_scoreboard_s *scoreboard, int *child_index);
+void fpm_scoreboard_proc_free(struct fpm_child_s *child);
+int fpm_scoreboard_proc_alloc(struct fpm_child_s *child);
 
 #ifdef HAVE_TIMES
 float fpm_scoreboard_get_tick();

sapi/fpm/fpm/fpm_status.c

@@ -498,10 +498,10 @@ int fpm_status_handle_request(void) /* {{{ */
 
 			first = 1;
 			for (i=0; i<scoreboard_p->nprocs; i++) {
-				if (!scoreboard_p->procs[i] || !scoreboard_p->procs[i]->used) {
+				if (!scoreboard_p->procs[i].used) {
 					continue;
 				}
-				proc = *scoreboard_p->procs[i];
+				proc = scoreboard_p->procs[i];
 
 				if (first) {
 					first = 0;

sapi/fpm/fpm/fpm_worker_pool.c

@@ -42,7 +42,7 @@ static void fpm_worker_pool_cleanup(int which, void *arg) /* {{{ */
 		fpm_worker_pool_config_free(wp->config);
 		fpm_children_free(wp->children);
 		if ((which & FPM_CLEANUP_CHILD) == 0 && fpm_globals.parent_pid == getpid()) {
-			fpm_scoreboard_free(wp->scoreboard);
+			fpm_scoreboard_free(wp);
 		}
 		fpm_worker_pool_free(wp);
 	}