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

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Date:   Wed,  9 Oct 2019 17:42:38 +0200
From:   Ilya Maximets <i.maximets@....org>
To:     netdev@...r.kernel.org
Cc:     bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S . Miller" <davem@...emloft.net>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Ilya Maximets <i.maximets@....org>
Subject: [PATCH bpf] libbpf: fix passing uninitialized bytes to setsockopt

'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.

Fixes: 10d30e301732 ("libbpf: add flags to umem config")
Signed-off-by: Ilya Maximets <i.maximets@....org>
---
 tools/lib/bpf/xsk.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
index a902838f9fcc..26d9db783560 100644
--- a/tools/lib/bpf/xsk.c
+++ b/tools/lib/bpf/xsk.c
@@ -139,7 +139,7 @@ int xsk_umem__create_v0_0_4(struct xsk_umem **umem_ptr, void *umem_area,
 			    const struct xsk_umem_config *usr_config)
 {
 	struct xdp_mmap_offsets off;
-	struct xdp_umem_reg mr;
+	struct xdp_umem_reg mr = {};
 	struct xsk_umem *umem;
 	socklen_t optlen;
 	void *map;
-- 
2.17.1