[PATCH 6.6.y] bnxt_en: don't leave an XDP program installed when the open fails

[Sasha Levin <sashal@kernel.org>]

From: Vaibhav Nagare <vnagare@redhat.com>

[ Upstream commit 78731b46967e3e7102b5cd5062bef185f3404b5c ]

bnxt_xdp_set() stores the new program and drops the reference on the old
one before reopening the NIC.  If bnxt_open_nic() then fails, ndo_bpf()
returns an error with the new program still in bp->xdp_prog.  The caller
treats the error as "nothing was installed" and drops its own reference,
so bp->xdp_prog is left pointing at a freed program and the next XDP
update dereferences it:

  BUG: unable to handle page fault for address: ff78ecc80ddd1038
  RIP: 0010:__bpf_prog_put+0x5/0x80
  Call Trace:
   bnxt_xdp_set+0xad/0x1b0 [bnxt_en]
   dev_xdp_propagate+0x36/0xa0
   bond_xdp_set+0xeb/0x2d0 [bonding]
   dev_xdp_install+0x1b1/0x350
   bpf_xdp_link_update+0xc5/0x1b0
   link_update+0x104/0x1e0
   __sys_bpf+0x662/0xcf0

Seen on a 6.12 based kernel after bnxt_alloc_mem() failed an order-4
allocation on a fragmented host:

  bnxt_en 0000:a0:00.1 ens4f1np1: nic open fail (rc: fffffff4)
  bond1: (slave ens4f1np1): Error -12 calling ndo_bpf

Bonding is not required to hit this; a plain XDP attach on a bnxt
interface takes the same path.

Restore the previous program when an attach or a replace fails, and
recompute the page-mode and XDP TX ring configuration from it.  The
configuration matters because bnxt_init_one_rx_ring() only assigns
rxr->xdp_prog in page mode, and __bnxt_set_rx_skb_mode() derives
dev->max_mtu from the installed program.  Release the old program only
once the change has been committed.

A detach is not undone.  dev_xdp_detach_link() clears the core's record
of the program even when the driver returns an error, so putting the
program back would leave the driver running a program the core has
already dropped.  If the reopen fails during a detach, bnxt_xdp_set()
therefore returns 0 with the device closed; bnxt_open_nic() has already
logged the failure.

Found in a crash dump; the change was not tested on hardware.

Fixes: c6d30e8391b8 ("bnxt_en: Add basic XDP support.")
Cc: stable@vger.kernel.org
Signed-off-by: Vaibhav Nagare <vnagare@redhat.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20261012072802.2153706-1-vnagare@redhat.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
[ sashal: replaced bnxt_xdp_apply_cfg() with an apply_cfg label inside bnxt_xdp_set() to reuse configuration without adding a function. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c | 25 +++++++++++++++----
 1 file changed, 20 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c b/drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c
index fc47d45805b75..85a9ffcc4fe06 100644
--- a/drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c
+++ b/drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c
@@ -388,6 +388,7 @@ static int bnxt_xdp_set(struct bnxt *bp, struct bpf_prog *prog)
 	struct net_device *dev = bp->dev;
 	int tx_xdp = 0, rc, tc;
 	struct bpf_prog *old;
+	int old_tx_xdp;
 
 	if (prog && !prog->aux->xdp_has_frags &&
 	    bp->dev->mtu > BNXT_MAX_PAGE_MODE_MTU) {
@@ -414,11 +415,12 @@ static int bnxt_xdp_set(struct bnxt *bp, struct bpf_prog *prog)
 	if (netif_running(dev))
 		bnxt_close_nic(bp, true, false);
 
+	old_tx_xdp = bp->tx_nr_rings_xdp;
 	old = xchg(&bp->xdp_prog, prog);
-	if (old)
-		bpf_prog_put(old);
 
-	if (prog) {
+apply_cfg:
+	tc = netdev_get_num_tc(dev) ? : 1;
+	if (bp->xdp_prog) {
 		bnxt_set_rx_skb_mode(bp, true);
 		xdp_features_set_redirect_target(dev, true);
 	} else {
@@ -431,8 +433,21 @@ static int bnxt_xdp_set(struct bnxt *bp, struct bpf_prog *prog)
 	bnxt_set_tpa_flags(bp);
 	bnxt_set_ring_params(bp);
 
-	if (netif_running(dev))
-		return bnxt_open_nic(bp, true, false);
+	if (rc)
+		return rc;
+
+	if (netif_running(dev)) {
+		rc = bnxt_open_nic(bp, true, false);
+		/* a detach cannot be undone, only an attach */
+		if (rc && prog) {
+			WRITE_ONCE(bp->xdp_prog, old);
+			tx_xdp = old_tx_xdp;
+			goto apply_cfg;
+		}
+	}
+
+	if (old)
+		bpf_prog_put(old);
 
 	return 0;
 }
-- 
2.53.0