| Message ID | 1474429700-130812-1-git-send-email-wangnan0@huawei.com |
|---|---|
| State | Superseded |
| Headers | show |
On 2016/9/21 11:48, Wang Nan wrote: > 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]; > > + Sorry for this blank line. Will fix it. > if (fgets(line, sizeof(line), fp) != NULL) > - value = (geteuid() != 0) ? > + value = ((geteuid() != 0) || (getuid() != 0)) ? > (atoi(line) != 0) : > (atoi(line) == 2); >
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);
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(-) -- 1.8.3.4