bpf: Explicitly memset the bpf_attr structure

commit 8096f229421f7b22433775e928d506f0342e5907 upstream.

For the bpf syscall, we are relying on the compiler to properly zero out
the bpf_attr union that we copy userspace data into. Unfortunately that
doesn't always work properly, padding and other oddities might not be
correctly zeroed, and in some tests odd things have been found when the
stack is pre-initialized to other values.

Fix this by explicitly memsetting the structure to 0 before using it.

Reported-by: Maciej Żenczykowski <maze@google.com>
Reported-by: John Stultz <john.stultz@linaro.org>
Reported-by: Alexander Potapenko <glider@google.com>
Reported-by: Alistair Delva <adelva@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://android-review.googlesource.com/c/kernel/common/+/1235490
Link: https://lore.kernel.org/bpf/20200320094813.GA421650@kroah.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 04fc1022ad9fbda9d87f846ecf727ea751ad23f2..fd3fd8d17ef55586adfd78265e56b15258f739f8 100644 (file)
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -667,7 +667,7 @@ static int bpf_obj_get(const union bpf_attr *attr)
 
 SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, size)
 {
-       union bpf_attr attr = {};
+       union bpf_attr attr;
        int err;
 
        if (sysctl_unprivileged_bpf_disabled && !capable(CAP_SYS_ADMIN))
@@ -703,6 +703,7 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz
        }
 
        /* copy attributes from user space, may be less than sizeof(bpf_attr) */
+       memset(&attr, 0, sizeof(attr));
        if (copy_from_user(&attr, uattr, size) != 0)
                return -EFAULT;