Re: [PATCH net v4] bnxt_en: don't leave an XDP program installed when the open fails

[Simon Horman]

On Mon, Oct 12, 2026 at 12:58:02PM +0530, Vaibhav Nagare wrote:
> 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@xxxxxxxxxxxxxxx
> Signed-off-by: Vaibhav Nagare <vnagare@xxxxxxxxxx>
> ---
>   v4:
>    - no functional change.  Correct the comment and commit message: the
>      core clears its record of the program on a failed detach, it does
>      not drop a reference itself, and note that a failed reopen during a
>      detach returns 0 with the device closed (Sashiko AI review)
>    - the same review notes the rollback does not restore the RX
>      aggregation-ring mode.  That is real but pre-existing: without this
>      patch the failed attach leaves the same bp->flags behind and the
>      next open fails the same way.  Restoring it needs a snapshot of
>      bp->flags, the LRO/GRO_HW feature bits and the ring parameters,
>      which is a separate change for net-next
>    - v3: https://lore.kernel.org/netdev/20261001142516.1386525-1-vnagare@xxxxxxxxxx/
>    - v2: https://lore.kernel.org/netdev/20260930070901.1218980-1-vnagare@xxxxxxxxxx/
>    - v1: https://lore.kernel.org/netdev/20260928131458.1012180-1-vnagare@xxxxxxxxxx/

Reviewed-by: Simon Horman <horms@xxxxxxxxxx>