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From: Masami Hiramatsu <mhiramat@kernel.org>
To: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>,
	linux-kernel@vger.kernel.org, Namhyung Kim <namhyung@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Hemant Kumar <hemant@linux.vnet.ibm.com>,
	Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>,
	Brendan Gregg <brendan.d.gregg@gmail.com>
Subject: [PATCH perf/core v9 01/16] perf-symbol: Introduce filename__readable to check readability
Date: Sun, 29 May 2016 00:15:13 +0900
Message-ID: <20160528151513.16098.97576.stgit@devbox> (raw)
In-Reply-To: <20160528151456.16098.90001.stgit@devbox>

Introduce filename__readable to check readability by opening
the file directly. Since the access(R_OK) just checks the
readability based on real UID/GID, it is ignored that the
effective UID/GID and capabilities for some special file (e.g.
/proc/kcore).
filename__readable() directly opens given file with O_RDONLY
so that the kernel checks it by effective UID/GID and capabilities.
---
 tools/perf/util/symbol.c |   32 ++++++++++++++++++++++----------
 1 file changed, 22 insertions(+), 10 deletions(-)

diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index 54c4ff2..a469346 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -1641,6 +1641,20 @@ static int find_matching_kcore(struct map *map, char *dir, size_t dir_sz)
 	return ret;
 }
 
+/*
+ * Use open(O_RDONLY) to check readability directly instead of access(R_OK)
+ * since access(R_OK) only checks with real UID/GID but open() use effective
+ * UID/GID and actual capabilities (e.g. /proc/kcore requires CAP_SYS_RAWIO).
+ */
+static bool filename__readable(const char *file)
+{
+	int fd = open(file, O_RDONLY);
+	if (fd < 0)
+		return false;
+	close(fd);
+	return true;
+}
+
 static char *dso__find_kallsyms(struct dso *dso, struct map *map)
 {
 	u8 host_build_id[BUILD_ID_SIZE];
@@ -1668,7 +1682,6 @@ static char *dso__find_kallsyms(struct dso *dso, struct map *map)
 	/* Use /proc/kallsyms if possible */
 	if (is_host) {
 		DIR *d;
-		int fd;
 
 		/* If no cached kcore go with /proc/kallsyms */
 		d = opendir(path);
@@ -1677,16 +1690,15 @@ static char *dso__find_kallsyms(struct dso *dso, struct map *map)
 		closedir(d);
 
 		/*
-		 * Do not check the build-id cache, until we know we cannot use
-		 * /proc/kcore.
+		 * Do not check the build-id cache, unless we know we cannot use
+		 * /proc/kcore or module maps don't match to /proc/kallsyms.
+		 * To check readability of /proc/kcore, do not use access(R_OK)
+		 * since /proc/kcore requires CAP_SYS_RAWIO to read and access
+		 * can't check it.
 		 */
-		fd = open("/proc/kcore", O_RDONLY);
-		if (fd != -1) {
-			close(fd);
-			/* If module maps match go with /proc/kallsyms */
-			if (!validate_kcore_addresses("/proc/kallsyms", map))
-				goto proc_kallsyms;
-		}
+		if (filename__readable("/proc/kcore") &&
+		    !validate_kcore_addresses("/proc/kallsyms", map))
+			goto proc_kallsyms;
 
 		/* Find kallsyms in build-id cache with kcore */
 		if (!find_matching_kcore(map, path, sizeof(path)))

  reply index

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-05-28 15:15 [PATCH perf/core v9 00/16] perf-probe --cache and SDT support Masami Hiramatsu
2016-05-28 15:15 ` Masami Hiramatsu [this message]
2016-05-30 16:03   ` [PATCH perf/core v9 01/16] perf-symbol: Introduce filename__readable to check readability Arnaldo Carvalho de Melo
2016-05-30 16:04     ` Arnaldo Carvalho de Melo
2016-05-31  5:54       ` Masami Hiramatsu
2016-06-02  6:34   ` [tip:perf/core] perf symbols: " tip-bot for Masami Hiramatsu
2016-05-28 15:15 ` [PATCH perf/core v9 02/16] perf symbol: Cleanup the code flow of dso__find_kallsyms Masami Hiramatsu
2016-06-02  6:34   ` [tip:perf/core] perf symbols: " tip-bot for Masami Hiramatsu
2016-05-28 15:15 ` [PATCH perf/core v9 03/16] perf-buildid-cache: Use path/to/bin/buildid/elf instead of path/to/bin/buildid Masami Hiramatsu
2016-06-02  6:35   ` [tip:perf/core] perf buildid-cache: " tip-bot for Masami Hiramatsu
2016-05-28 15:15 ` [PATCH perf/core v9 04/16] perf probe: Add --cache option to cache the probe definitions Masami Hiramatsu
2016-05-28 15:15 ` [PATCH perf/core v9 05/16] perf probe: Use cache entry if possible Masami Hiramatsu
2016-05-28 15:16 ` [PATCH perf/core v9 06/16] perf probe: Show all cached probes Masami Hiramatsu
2016-05-28 15:16 ` [PATCH perf/core v9 07/16] perf probe: Remove caches when --cache is given Masami Hiramatsu
2016-05-28 15:16 ` [PATCH perf/core v9 08/16] perf/sdt: ELF support for SDT Masami Hiramatsu
2016-05-28 15:16 ` [PATCH perf/core v9 09/16] perf probe: Add group name support Masami Hiramatsu
2016-05-28 15:16 ` [PATCH perf/core v9 10/16] perf buildid-cache: Scan and import user SDT events to probe cache Masami Hiramatsu
2016-05-28 15:16 ` [PATCH perf/core v9 11/16] perf probe: Accept %sdt and %cached event name Masami Hiramatsu
2016-05-28 15:17 ` [PATCH perf/core v9 12/16] perf-list: Show SDT and pre-cached events Masami Hiramatsu
2016-05-28 15:17 ` [PATCH perf/core v9 13/16] perf-list: Skip SDTs placed in invalid binaries Masami Hiramatsu
2016-05-28 15:17 ` [PATCH perf/core v9 14/16] perf probe: Allow wildcard for cached events Masami Hiramatsu
2016-05-28 15:17 ` [PATCH perf/core v9 15/16] perf probe: Support @BUILDID or @FILE suffix for SDT events Masami Hiramatsu
2016-05-28 15:17 ` [PATCH perf/core v9 16/16] perf probe: Support a special SDT probe format Masami Hiramatsu
2016-05-30  3:54 ` [PATCH perf/core v9 00/16] perf-probe --cache and SDT support Namhyung Kim
2016-05-30 14:31   ` Masami Hiramatsu
2016-05-30 16:10   ` Arnaldo Carvalho de Melo
2016-05-31  9:01     ` Masami Hiramatsu
2016-05-31 13:40       ` Arnaldo Carvalho de Melo
2016-05-30 16:22 ` Arnaldo Carvalho de Melo
2016-05-30 16:30   ` Arnaldo Carvalho de Melo
2016-05-31  8:00     ` Masami Hiramatsu
2016-05-31 13:39       ` Arnaldo Carvalho de Melo
2016-05-31 16:30         ` Hemant Kumar

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