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SubjectRe: [PATCH] perf record: Fix segfault when running with suid and kptr_restrict is 1
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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);
>


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