From: David Ahern <dsahern@gmail.com>
Date: Sun, 12 Apr 2020 07:32:04 -0600
Subject: xdp: Reset prog in dev_change_xdp_fd when fd is negative
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Patch-mainline: v5.7-rc2
Git-commit: dfa74909cb6b846cbdabfc2c3c7de1d507fca075
References: bsc#1177028

The commit mentioned in the Fixes tag reuses the local prog variable
when looking up an expected_fd. The variable is not reset when fd < 0
causing a detach with the expected_fd set to actually call
dev_xdp_install for the existing program. The end result is that the
detach does not happen.

Fixes: 92234c8f15c8 ("xdp: Support specifying expected existing program when attaching XDP")
Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/bpf/20200412133204.43847-1-dsahern@kernel.org
Acked-by: Gary Lin <glin@suse.com>
---
 net/core/dev.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -8674,8 +8674,8 @@ int dev_change_xdp_fd(struct net_device
 	const struct net_device_ops *ops = dev->netdev_ops;
 	enum bpf_netdev_command query;
 	u32 prog_id, expected_id = 0;
-	struct bpf_prog *prog = NULL;
 	bpf_op_t bpf_op, bpf_chk;
+	struct bpf_prog *prog;
 	bool offload;
 	int err;
 
@@ -8741,6 +8741,7 @@ int dev_change_xdp_fd(struct net_device
 	} else {
 		if (!prog_id)
 			return 0;
+		prog = NULL;
 	}
 
 	err = dev_xdp_install(dev, bpf_op, extack, flags, prog);