[PATCH bpf v2] libbpf: fix passing uninitialized bytes to setsockopt

[Ilya Maximets]

'struct xdp_umem_reg' has 4 bytes of padding at the end that makes
valgrind complain about passing uninitialized stack memory to the
syscall:

  Syscall param socketcall.setsockopt() points to uninitialised byte(s)
    at 0x4E7AB7E: setsockopt (in /usr/lib64/libc-2.29.so)
    by 0x4BDE035: xsk_umem__create@@LIBBPF_0.0.4 (xsk.c:172)
  Uninitialised value was created by a stack allocation
    at 0x4BDDEBA: xsk_umem__create@@LIBBPF_0.0.4 (xsk.c:140)

Padding bytes appeared after introducing of a new 'flags' field.
memset() is required to clear them.

Fixes: 10d30e301732 ("libbpf: add flags to umem config")
Signed-off-by: Ilya Maximets <i.maxim...@ovn.org>
---

Version 2:
  * Struct initializer replaced with explicit memset(). [Andrii]

 tools/lib/bpf/xsk.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
index a902838f9fcc..9d5348086203 100644
--- a/tools/lib/bpf/xsk.c
+++ b/tools/lib/bpf/xsk.c
@@ -163,6 +163,7 @@ int xsk_umem__create_v0_0_4(struct xsk_umem **umem_ptr, 
void *umem_area,
        umem->umem_area = umem_area;
        xsk_set_umem_config(&umem->config, usr_config);
 
+       memset(&mr, 0, sizeof(mr));
        mr.addr = (uintptr_t)umem_area;
        mr.len = size;
        mr.chunk_size = umem->config.frame_size;
-- 
2.17.1