linux-kernel - [PATCH 3/3] perf: Use CAP_SYSLOG with kptr

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Date:   Tue, 2 Jul 2019 20:10:05 -0400
From:   Igor Lubashev <ilubashe@...mai.com>
To:     <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>
CC:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        <linux-arm-kernel@...ts.infradead.org>,
        James Morris <jmorris@...ei.org>,
        Igor Lubashev <ilubashe@...mai.com>
Subject: [PATCH 3/3] perf: Use CAP_SYSLOG with kptr_restrict checks

Kernel is using CAP_SYSLOG capcbility instead of uid==0 and euid==0 when
checking kptr_restrict. Make perf do the same.

Also, the kernel is a more restrictive than "no restrictions" in case of
kptr_restrict==0, so add the same logic to perf.

Signed-off-by: Igor Lubashev <ilubashe@...mai.com>
---
 tools/perf/util/symbol.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index 5cbad55cd99d..fd68dae3f58e 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -4,6 +4,7 @@
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
+#include <linux/capability.h>
 #include <linux/kernel.h>
 #include <linux/mman.h>
 #include <linux/time64.h>
@@ -15,8 +16,10 @@
 #include <inttypes.h>
 #include "annotate.h"
 #include "build-id.h"
+#include "cap.h"
 #include "util.h"
 #include "debug.h"
+#include "event.h"
 #include "machine.h"
 #include "map.h"
 #include "symbol.h"
@@ -889,7 +892,11 @@ bool symbol__restricted_filename(const char *filename,
 {
 	bool restricted = false;
 
-	if (symbol_conf.kptr_restrict) {
+	/* Per kernel/kallsyms.c:
+	 * we also restrict when perf_event_paranoid > 1 w/o CAP_SYSLOG
+	 */
+	if (symbol_conf.kptr_restrict ||
+	    (perf_event_paranoid() > 1 && !perf_cap__capable(CAP_SYSLOG))) {
 		char *r = realpath(filename, NULL);
 
 		if (r != NULL) {
@@ -2100,9 +2107,9 @@ static bool symbol__read_kptr_restrict(void)
 		char line[8];
 
 		if (fgets(line, sizeof(line), fp) != NULL)
-			value = ((geteuid() != 0) || (getuid() != 0)) ?
-					(atoi(line) != 0) :
-					(atoi(line) == 2);
+			value = perf_cap__capable(CAP_SYSLOG) ?
+					(atoi(line) >= 2) :
+					(atoi(line) != 0);
 
 		fclose(fp);
 	}
-- 
2.7.4