perf namespaces: Add reference count checking

Add reference count checking controlled by REFCNT_CHECKING ifdef. The
reference count checking interposes an allocated pointer between the
reference counted struct on a get and frees the pointer on a put.
Accesses after a put cause faults and use after free, missed puts are
caughts as leaks and double puts are double frees.

This checking helped resolve a memory leak and use after free:
https://lore.kernel.org/linux-perf-users/CAP-5=fWZH20L4kv-BwVtGLwR=Em3AOOT+Q4QGivvQuYn5AsPRg@mail.gmail.com/Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexey Bayduraev <alexey.v.bayduraev@linux.intel.com>
Cc: Dmitriy Vyukov <dvyukov@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Riccardo Mancini <rickyman7@gmail.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: Stephen Brennan <stephen.s.brennan@oracle.com>
Link: https://lore.kernel.org/lkml/20230407230405.2931830-4-irogers@google.com
[ Extracted from a larger patch ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/namespaces.c

@@ -60,7 +60,7 @@ void namespaces__free(struct namespaces *namespaces)
 	free(namespaces);
 }
 
-static int nsinfo__get_nspid(struct nsinfo *nsi, const char *path)
+static int nsinfo__get_nspid(pid_t *tgid, pid_t *nstgid, bool *in_pidns, const char *path)
 {
 	FILE *f = NULL;
 	char *statln = NULL;
@@ -74,19 +74,18 @@ static int nsinfo__get_nspid(struct nsinfo *nsi, const char *path)
 	while (getline(&statln, &linesz, f) != -1) {
 		/* Use tgid if CONFIG_PID_NS is not defined. */
 		if (strstr(statln, "Tgid:") != NULL) {
-			nsi->tgid = (pid_t)strtol(strrchr(statln, '\t'),
-						     NULL, 10);
-			nsi->nstgid = nsinfo__tgid(nsi);
+			*tgid = (pid_t)strtol(strrchr(statln, '\t'), NULL, 10);
+			*nstgid = *tgid;
 		}
 
 		if (strstr(statln, "NStgid:") != NULL) {
 			nspid = strrchr(statln, '\t');
-			nsi->nstgid = (pid_t)strtol(nspid, NULL, 10);
+			*nstgid = (pid_t)strtol(nspid, NULL, 10);
 			/*
 			 * If innermost tgid is not the first, process is in a different
 			 * PID namespace.
 			 */
-			nsi->in_pidns = (statln + sizeof("NStgid:") - 1) != nspid;
+			*in_pidns = (statln + sizeof("NStgid:") - 1) != nspid;
 			break;
 		}
 	}
@@ -121,8 +120,8 @@ int nsinfo__init(struct nsinfo *nsi)
 	 * want to switch as part of looking up dso/map data.
 	 */
 	if (old_stat.st_ino != new_stat.st_ino) {
-		nsi->need_setns = true;
-		nsi->mntns_path = newns;
+		RC_CHK_ACCESS(nsi)->need_setns = true;
+		RC_CHK_ACCESS(nsi)->mntns_path = newns;
 		newns = NULL;
 	}
 
@@ -132,13 +131,26 @@ int nsinfo__init(struct nsinfo *nsi)
 	if (snprintf(spath, PATH_MAX, "/proc/%d/status", nsinfo__pid(nsi)) >= PATH_MAX)
 		goto out;
 
-	rv = nsinfo__get_nspid(nsi, spath);
+	rv = nsinfo__get_nspid(&RC_CHK_ACCESS(nsi)->tgid, &RC_CHK_ACCESS(nsi)->nstgid,
+			       &RC_CHK_ACCESS(nsi)->in_pidns, spath);
 
 out:
 	free(newns);
 	return rv;
 }
 
+static struct nsinfo *nsinfo__alloc(void)
+{
+	struct nsinfo *res;
+	RC_STRUCT(nsinfo) *nsi;
+
+	nsi = calloc(1, sizeof(*nsi));
+	if (ADD_RC_CHK(res, nsi))
+		refcount_set(&nsi->refcnt, 1);
+
+	return res;
+}
+
 struct nsinfo *nsinfo__new(pid_t pid)
 {
 	struct nsinfo *nsi;
@@ -146,22 +158,21 @@ struct nsinfo *nsinfo__new(pid_t pid)
 	if (pid == 0)
 		return NULL;
 
-	nsi = calloc(1, sizeof(*nsi));
-	if (nsi != NULL) {
-		nsi->pid = pid;
-		nsi->tgid = pid;
-		nsi->nstgid = pid;
-		nsi->need_setns = false;
-		nsi->in_pidns = false;
-		/* Init may fail if the process exits while we're trying to look
-		 * at its proc information.  In that case, save the pid but
-		 * don't try to enter the namespace.
-		 */
-		if (nsinfo__init(nsi) == -1)
-			nsi->need_setns = false;
+	nsi = nsinfo__alloc();
+	if (!nsi)
+		return NULL;
 
-		refcount_set(&nsi->refcnt, 1);
-	}
+	RC_CHK_ACCESS(nsi)->pid = pid;
+	RC_CHK_ACCESS(nsi)->tgid = pid;
+	RC_CHK_ACCESS(nsi)->nstgid = pid;
+	RC_CHK_ACCESS(nsi)->need_setns = false;
+	RC_CHK_ACCESS(nsi)->in_pidns = false;
+	/* Init may fail if the process exits while we're trying to look at its
+	 * proc information. In that case, save the pid but don't try to enter
+	 * the namespace.
+	 */
+	if (nsinfo__init(nsi) == -1)
+		RC_CHK_ACCESS(nsi)->need_setns = false;
 
 	return nsi;
 }
@@ -173,21 +184,21 @@ struct nsinfo *nsinfo__copy(const struct nsinfo *nsi)
 	if (nsi == NULL)
 		return NULL;
 
-	nnsi = calloc(1, sizeof(*nnsi));
-	if (nnsi != NULL) {
-		nnsi->pid = nsinfo__pid(nsi);
-		nnsi->tgid = nsinfo__tgid(nsi);
-		nnsi->nstgid = nsinfo__nstgid(nsi);
-		nnsi->need_setns = nsinfo__need_setns(nsi);
-		nnsi->in_pidns = nsinfo__in_pidns(nsi);
-		if (nsi->mntns_path) {
-			nnsi->mntns_path = strdup(nsi->mntns_path);
-			if (!nnsi->mntns_path) {
-				free(nnsi);
-				return NULL;
-			}
+	nnsi = nsinfo__alloc();
+	if (!nnsi)
+		return NULL;
+
+	RC_CHK_ACCESS(nnsi)->pid = nsinfo__pid(nsi);
+	RC_CHK_ACCESS(nnsi)->tgid = nsinfo__tgid(nsi);
+	RC_CHK_ACCESS(nnsi)->nstgid = nsinfo__nstgid(nsi);
+	RC_CHK_ACCESS(nnsi)->need_setns = nsinfo__need_setns(nsi);
+	RC_CHK_ACCESS(nnsi)->in_pidns = nsinfo__in_pidns(nsi);
+	if (RC_CHK_ACCESS(nsi)->mntns_path) {
+		RC_CHK_ACCESS(nnsi)->mntns_path = strdup(RC_CHK_ACCESS(nsi)->mntns_path);
+		if (!RC_CHK_ACCESS(nnsi)->mntns_path) {
+			nsinfo__put(nnsi);
+			return NULL;
 		}
-		refcount_set(&nnsi->refcnt, 1);
 	}
 
 	return nnsi;
@@ -195,51 +206,60 @@ struct nsinfo *nsinfo__copy(const struct nsinfo *nsi)
 
 static void nsinfo__delete(struct nsinfo *nsi)
 {
-	zfree(&nsi->mntns_path);
-	free(nsi);
+	if (nsi) {
+		WARN_ONCE(refcount_read(&RC_CHK_ACCESS(nsi)->refcnt) != 0,
+			"nsinfo refcnt unbalanced\n");
+		zfree(&RC_CHK_ACCESS(nsi)->mntns_path);
+		RC_CHK_FREE(nsi);
+	}
 }
 
 struct nsinfo *nsinfo__get(struct nsinfo *nsi)
 {
-	if (nsi)
-		refcount_inc(&nsi->refcnt);
-	return nsi;
+	struct nsinfo *result;
+
+	if (RC_CHK_GET(result, nsi))
+		refcount_inc(&RC_CHK_ACCESS(nsi)->refcnt);
+
+	return result;
 }
 
 void nsinfo__put(struct nsinfo *nsi)
 {
-	if (nsi && refcount_dec_and_test(&nsi->refcnt))
+	if (nsi && refcount_dec_and_test(&RC_CHK_ACCESS(nsi)->refcnt))
 		nsinfo__delete(nsi);
+	else
+		RC_CHK_PUT(nsi);
 }
 
 bool nsinfo__need_setns(const struct nsinfo *nsi)
 {
-        return nsi->need_setns;
+	return RC_CHK_ACCESS(nsi)->need_setns;
 }
 
 void nsinfo__clear_need_setns(struct nsinfo *nsi)
 {
-        nsi->need_setns = false;
+	RC_CHK_ACCESS(nsi)->need_setns = false;
 }
 
 pid_t nsinfo__tgid(const struct nsinfo  *nsi)
 {
-        return nsi->tgid;
+	return RC_CHK_ACCESS(nsi)->tgid;
 }
 
 pid_t nsinfo__nstgid(const struct nsinfo  *nsi)
 {
-        return nsi->nstgid;
+	return RC_CHK_ACCESS(nsi)->nstgid;
 }
 
 pid_t nsinfo__pid(const struct nsinfo  *nsi)
 {
-        return nsi->pid;
+	return RC_CHK_ACCESS(nsi)->pid;
 }
 
 pid_t nsinfo__in_pidns(const struct nsinfo  *nsi)
 {
-        return nsi->in_pidns;
+	return RC_CHK_ACCESS(nsi)->in_pidns;
 }
 
 void nsinfo__mountns_enter(struct nsinfo *nsi,
@@ -256,7 +276,7 @@ void nsinfo__mountns_enter(struct nsinfo *nsi,
 	nc->oldns = -1;
 	nc->newns = -1;
 
-	if (!nsi || !nsi->need_setns)
+	if (!nsi || !RC_CHK_ACCESS(nsi)->need_setns)
 		return;
 
 	if (snprintf(curpath, PATH_MAX, "/proc/self/ns/mnt") >= PATH_MAX)
@@ -270,7 +290,7 @@ void nsinfo__mountns_enter(struct nsinfo *nsi,
 	if (oldns < 0)
 		goto errout;
 
-	newns = open(nsi->mntns_path, O_RDONLY);
+	newns = open(RC_CHK_ACCESS(nsi)->mntns_path, O_RDONLY);
 	if (newns < 0)
 		goto errout;
 
@@ -339,9 +359,9 @@ int nsinfo__stat(const char *filename, struct stat *st, struct nsinfo *nsi)
 
 bool nsinfo__is_in_root_namespace(void)
 {
-	struct nsinfo nsi;
+	pid_t tgid = 0, nstgid = 0;
+	bool in_pidns = false;
 
-	memset(&nsi, 0x0, sizeof(nsi));
-	nsinfo__get_nspid(&nsi, "/proc/self/status");
-	return !nsi.in_pidns;
+	nsinfo__get_nspid(&tgid, &nstgid, &in_pidns, "/proc/self/status");
+	return !in_pidns;
 }

tools/perf/util/namespaces.h

@@ -13,6 +13,7 @@
 #include <linux/perf_event.h>
 #include <linux/refcount.h>
 #include <linux/types.h>
+#include <internal/rc_check.h>
 
 #ifndef HAVE_SETNS_SUPPORT
 int setns(int fd, int nstype);
@@ -29,7 +30,7 @@ struct namespaces {
 struct namespaces *namespaces__new(struct perf_record_namespaces *event);
 void namespaces__free(struct namespaces *namespaces);
 
-struct nsinfo {
+DECLARE_RC_STRUCT(nsinfo) {
 	pid_t			pid;
 	pid_t			tgid;
 	pid_t			nstgid;