Merge branch 'bpf-xdp-offload-fixes'

Toke Høiland-Jørgensen says:

====================
This series restores the test_offload.py selftest to working order. It seems a
number of subtle behavioural changes have crept into various subsystems which
broke test_offload.py in a number of ways. Most of these are fairly benign
changes where small adjustments to the test script seems to be the best fix,
but one is an actual kernel bug that I've observed in the wild caused by a bad
interaction between xdp_attachment_flags_ok() and the rework of XDP program
handling in the core netdev code.

Patch 1 fixes the bug by removing xdp_attachment_flags_ok(), and the reminder of
the patches are adjustments to test_offload.py, including a new feature for
netdevsim to force a BPF verification fail. Please see the individual patches
for details.

Changelog:

v4:
  - Accidentally truncated the Fixes: hashes in patches 3/4 to 11 chars
v3:
  - Add Fixes: tags
v2:
  - Replace xdp_attachment_flags_ok() with a check in dev_xdp_attach()
  - Better packing of struct nsim_dev
====================

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

1 files changed, 20 insertions, 2 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 8588ade790cb..38412e70f761 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -8917,6 +8917,17 @@ static struct bpf_prog *dev_xdp_prog(struct net_device *dev,
 	return dev->xdp_state[mode].prog;
 }
 
+static u8 dev_xdp_prog_count(struct net_device *dev)
+{
+	u8 count = 0;
+	int i;
+
+	for (i = 0; i < __MAX_XDP_MODE; i++)
+		if (dev->xdp_state[i].prog || dev->xdp_state[i].link)
+			count++;
+	return count;
+}
+
 u32 dev_xdp_prog_id(struct net_device *dev, enum bpf_xdp_mode mode)
 {
 	struct bpf_prog *prog = dev_xdp_prog(dev, mode);
@@ -9007,6 +9018,7 @@ static int dev_xdp_attach(struct net_device *dev, struct netlink_ext_ack *extack
 			  struct bpf_xdp_link *link, struct bpf_prog *new_prog,
 			  struct bpf_prog *old_prog, u32 flags)
 {
+	unsigned int num_modes = hweight32(flags & XDP_FLAGS_MODES);
 	struct bpf_prog *cur_prog;
 	enum bpf_xdp_mode mode;
 	bpf_op_t bpf_op;
@@ -9022,11 +9034,17 @@ static int dev_xdp_attach(struct net_device *dev, struct netlink_ext_ack *extack
 		NL_SET_ERR_MSG(extack, "Invalid XDP flags for BPF link attachment");
 		return -EINVAL;
 	}
-	/* just one XDP mode bit should be set, zero defaults to SKB mode */
-	if (hweight32(flags & XDP_FLAGS_MODES) > 1) {
+	/* just one XDP mode bit should be set, zero defaults to drv/skb mode */
+	if (num_modes > 1) {
 		NL_SET_ERR_MSG(extack, "Only one XDP mode flag can be set");
 		return -EINVAL;
 	}
+	/* avoid ambiguity if offload + drv/skb mode progs are both loaded */
+	if (!num_modes && dev_xdp_prog_count(dev) > 1) {
+		NL_SET_ERR_MSG(extack,
+			       "More than one program loaded, unset mode is ambiguous");
+		return -EINVAL;
+	}
 	/* old_prog != NULL implies XDP_FLAGS_REPLACE is set */
 	if (old_prog && !(flags & XDP_FLAGS_REPLACE)) {
 		NL_SET_ERR_MSG(extack, "XDP_FLAGS_REPLACE is not specified");