Subject: [PATCH 05/37] perf symbols: Use CAP_SYSLOG with kptr_restrict checks

From: Arnaldo Carvalho de Melo <[email-masked]>
Date: Thu, 29 Aug 2019 11:38:45 -0300

From: Igor Lubashev <[email-masked]>

The kernel is using CAP_SYSLOG capability 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 <[email-masked]>
Tested-by: Mathieu Poirier <[email-masked]>
Cc: Alexander Shishkin <[email-masked]>
Cc: Alexey Budankov <[email-masked]>
Cc: James Morris <[email-masked]>
Cc: Jiri Olsa <[email-masked]>
Cc: Namhyung Kim <[email-masked]>
Cc: Peter Zijlstra <[email-masked]>
Cc: Suzuki Poulouse <[email-masked]>
Cc: [email-masked]
Link: http://lkml.kernel.org/r/[email-masked]
Signed-off-by: Arnaldo Carvalho de Melo <[email-masked]>
---
 tools/perf/util/symbol.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index 4efde7879474..035f2e75728c 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"
@@ -2195,13 +2198,19 @@ 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);
 	}
 
+	/* Per kernel/kallsyms.c:
+	 * we also restrict when perf_event_paranoid > 1 w/o CAP_SYSLOG
+	 */
+	if (perf_event_paranoid() > 1 && !perf_cap__capable(CAP_SYSLOG))
+		value = true;
+
 	return value;
 }
 
-- 
2.21.0

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