netdev - [PATCH bpf] libbpf: fix potential NULL pointer dereference

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Date:   Thu,  8 Apr 2021 05:20:09 +0000
From:   Ciara Loftus <ciara.loftus@...el.com>
To:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        magnus.karlsson@...el.com, bjorn@...nel.org,
        andrii.nakryiko@...il.com, alexei.starovoitov@...il.com
Cc:     Ciara Loftus <ciara.loftus@...el.com>
Subject: [PATCH bpf] libbpf: fix potential NULL pointer dereference

Wait until after the UMEM is checked for null to dereference it.

Fixes: 43f1bc1efff1 ("libbpf: Restore umem state after socket create failure")

Signed-off-by: Ciara Loftus <ciara.loftus@...el.com>
---
 tools/lib/bpf/xsk.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
index d24b5cc720ec..770040d1f893 100644
--- a/tools/lib/bpf/xsk.c
+++ b/tools/lib/bpf/xsk.c
@@ -858,12 +858,14 @@ int xsk_socket__create_shared(struct xsk_socket **xsk_ptr,
 	struct xsk_socket *xsk;
 	struct xsk_ctx *ctx;
 	int err, ifindex;
-	bool unmap = umem->fill_save != fill;
+	bool unmap;
 	bool rx_setup_done = false, tx_setup_done = false;
 
 	if (!umem || !xsk_ptr || !(rx || tx))
 		return -EFAULT;
 
+	unmap = umem->fill_save != fill;
+
 	xsk = calloc(1, sizeof(*xsk));
 	if (!xsk)
 		return -ENOMEM;
-- 
2.17.1