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

[Vaibhav Nagare <nagarevaibhav@gmail.com>]

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 the open fails and release it only
once the change has been committed.  The ring and feature configuration
is left as computed for the rejected program; the device stays down on
this path, and reconciling it is left for a separate change.

Fixes: c6d30e8391b8 ("bnxt_en: Add basic XDP support.")
Cc: stable@vger.kernel.org
Signed-off-by: Vaibhav Nagare <vnagare@redhat.com>
---
 drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c b/drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c
index 9e5009be8e98..f30ce644e377 100644
--- a/drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c
+++ b/drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c
@@ -419,8 +419,6 @@ static int bnxt_xdp_set(struct bnxt *bp, struct bpf_prog *prog)
 		bnxt_close_nic(bp, true, false);
 
 	old = xchg(&bp->xdp_prog, prog);
-	if (old)
-		bpf_prog_put(old);
 
 	if (prog) {
 		bnxt_set_rx_skb_mode(bp, true);
@@ -435,8 +433,16 @@ 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 (netif_running(dev)) {
+		rc = bnxt_open_nic(bp, true, false);
+		if (rc) {
+			WRITE_ONCE(bp->xdp_prog, old);
+			return rc;
+		}
+	}
+
+	if (old)
+		bpf_prog_put(old);
 
 	return 0;
 }
-- 
2.55.0