Messages in this thread Patch in this message | | | From | Wang Nan <> | Subject | [PATCH] perf record: Fix segfault when running with suid and kptr_restrict is 1 | Date | Wed, 21 Sep 2016 03:48:20 +0000 |
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Before this patch perf panic if kptr_restrict set to 1 and perf is owned by root with suid set:
$ whoami wangnan $ ls -l ./perf -rwsr-xr-x 1 root root 19781908 Sep 21 19:29 /home/wangnan/perf $ cat /proc/sys/kernel/kptr_restrict 1 $ cat /proc/sys/kernel/perf_event_paranoid -1 $ ./perf record -a Segmentation fault (core dumped)
The reason is perf assumes it is allowed to read kptr from /proc/kallsyms when euid is root, but in fact kernel doesn't allow it reading kptr when euid and uid are not match with each other:
$ cp /bin/cat . $ sudo chown root:root ./cat $ sudo chmod u+s ./cat $ cat /proc/kallsyms | grep do_fork 0000000000000000 T _do_fork <--- kptr is hidden even euid is root $ sudo cat /proc/kallsyms | grep do_fork ffffffff81080230 T _do_fork
See lib/vsprintf.c for kernel side code.
This patch fixes this problem by checking both uid and euid.
Signed-off-by: Wang Nan <wangnan0@huawei.com> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> --- tools/perf/util/symbol.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c index 19c9c55..9528702 100644 --- a/tools/perf/util/symbol.c +++ b/tools/perf/util/symbol.c @@ -1946,8 +1946,9 @@ static bool symbol__read_kptr_restrict(void) if (fp != NULL) { char line[8]; + if (fgets(line, sizeof(line), fp) != NULL) - value = (geteuid() != 0) ? + value = ((geteuid() != 0) || (getuid() != 0)) ? (atoi(line) != 0) : (atoi(line) == 2); -- 1.8.3.4
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