prlimit: do_prlimit needs to have a speculation check

commit 739790605705ddcf18f21782b9c99ad7d53a8c11 upstream.

do_prlimit() adds the user-controlled resource value to a pointer that
will subsequently be dereferenced.  In order to help prevent this
codepath from being used as a spectre "gadget" a barrier needs to be
added after checking the range.

Reported-by: Jordy Zomer <jordyzomer@google.com>
Tested-by: Jordy Zomer <jordyzomer@google.com>
Suggested-by: Linus Torvalds <torvalds@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/sys.c b/kernel/sys.c
index b075fe84eb5a57759397e1441d7bffa12fb814fa..f6d6ce8da3e4ae8a26f9f6d3386d834caf0fd280 100644 (file)
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1534,6 +1534,8 @@ int do_prlimit(struct task_struct *tsk, unsigned int resource,
 
        if (resource >= RLIM_NLIMITS)
                return -EINVAL;
+       resource = array_index_nospec(resource, RLIM_NLIMITS);
+
        if (new_rlim) {
                if (new_rlim->rlim_cur > new_rlim->rlim_max)
                        return -EINVAL;