On Fri, Mar 20, 2020 at 04:24:32PM +0100, Daniel Borkmann wrote: > On 3/20/20 10:48 AM, Greg Kroah-Hartman wrote: > > 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@xxxxxxxxxx> > > Reported-by: John Stultz <john.stultz@xxxxxxxxxx> > > Reported-by: Alexander Potapenko <glider@xxxxxxxxxx> > > Reported-by: Alistair Delva <adelva@xxxxxxxxxx> > > Cc: stable <stable@xxxxxxxxxxxxxxx> > > Link: https://android-review.googlesource.com/c/kernel/common/+/1235490 > > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> > > --- > > kernel/bpf/syscall.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c > > index a91ad518c050..a4b1de8ea409 100644 > > --- a/kernel/bpf/syscall.c > > +++ b/kernel/bpf/syscall.c > > @@ -3354,7 +3354,7 @@ static int bpf_map_do_batch(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)) > > @@ -3366,6 +3366,7 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz > > size = min_t(u32, size, sizeof(attr)); > > /* copy attributes from user space, may be less than sizeof(bpf_attr) */ > > + memset(&attr, 0, sizeof(attr)); > > Thanks for the fix, there are a few more of these places. We would also need > to cover: > > - bpf_prog_get_info_by_fd() Unless I am mistaken, struct bpf_prog_info is packed fully, with no holes, so this shouldn't be an issue there. > - bpf_map_get_info_by_fd() No padding in struct bpf_map_info that I can see, so I doubt this is needed there. > - btf_get_info_by_fd() There is no padding in struct bpf_btf_info, so that's not needed there, but I can add it if you really want. I can change these, but I don't think that there currently is a bug in those functions, unlike with "union bpf_attr" which, as Yonghong points out, is tripping on the CHECK_ATTR() test later on. thanks, greg k-h