[PATCH net] net: mana: restore the XDP program pointer when pre-allocation fails

mana_xdp_set() publishes the new program into apc->bpf_prog before it
allocates anything, because mana_pre_alloc_rxbufs() sizes the buffers
from it via mana_get_rxbuf_cfg(). When that allocation fails the
function returns the error directly, skipping the err_dealloc_rxbuffs
label which is the only place that restores the previous pointer.

The attach is reported as failed, so the BPF core drops the reference it
held for the caller and the program can be freed, while apc->bpf_prog
still points at it. The next consumer of mana_xdp_get() - typically
mana_chn_setxdp() from mana_alloc_queues() on the following ifup, or
after a TX timeout reset - then calls bpf_prog_add() on freed memory.

This is reachable from an ordinary "ip link set dev ethX xdp obj ..."
whenever the per-queue RX buffer pre-allocation cannot be satisfied.

Restore the previous program on that error path.

Fixes: 730ff06d3f5c ("net: mana: Use page pool fragments for RX buffers instead of full pages to improve memory efficiency.")
Signed-off-by: Long Li <redacted>
---
 drivers/net/ethernet/microsoft/mana/mana_bpf.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/ethernet/microsoft/mana/mana_bpf.c b/drivers/net/ethernet/microsoft/mana/mana_bpf.c
index 53308e139cbe917b074dd381c83546fc74d7b79f..5c9961ee9747ab7747ce2f51eb40f3e7a55510cf 100644
--- a/drivers/net/ethernet/microsoft/mana/mana_bpf.c
+++ b/drivers/net/ethernet/microsoft/mana/mana_bpf.c

@@ -208,6 +208,7 @@ static int mana_xdp_set(struct net_device *ndev, struct bpf_prog *prog,
 		if (err) {
 			NL_SET_ERR_MSG_MOD(extack,
 					   "XDP: Insufficient memory for tx/rx re-config");
+			apc->bpf_prog = old_prog;
 			return err;
 		}
 

-- 
2.43.0

On Fri, Sep 04, 2026 at 01:26:40PM -0700, Long Li wrote:

mana_xdp_set() publishes the new program into apc->bpf_prog before it
allocates anything, because mana_pre_alloc_rxbufs() sizes the buffers
from it via mana_get_rxbuf_cfg(). When that allocation fails the
function returns the error directly, skipping the err_dealloc_rxbuffs
label which is the only place that restores the previous pointer.

The attach is reported as failed, so the BPF core drops the reference it
held for the caller and the program can be freed, while apc->bpf_prog
still points at it. The next consumer of mana_xdp_get() - typically
mana_chn_setxdp() from mana_alloc_queues() on the following ifup, or
after a TX timeout reset - then calls bpf_prog_add() on freed memory.

This is reachable from an ordinary "ip link set dev ethX xdp obj ..."
whenever the per-queue RX buffer pre-allocation cannot be satisfied.

Restore the previous program on that error path.

Fixes: 730ff06d3f5c ("net: mana: Use page pool fragments for RX buffers instead of full pages to improve memory efficiency.")
Signed-off-by: Long Li <redacted>

Reviewed-by: Simon Horman <horms@kernel.org>

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski [off-list ref]:

On Fri,  4 Sep 2026 13:26:40 -0700 you wrote:

mana_xdp_set() publishes the new program into apc->bpf_prog before it
allocates anything, because mana_pre_alloc_rxbufs() sizes the buffers
from it via mana_get_rxbuf_cfg(). When that allocation fails the
function returns the error directly, skipping the err_dealloc_rxbuffs
label which is the only place that restores the previous pointer.

The attach is reported as failed, so the BPF core drops the reference it
held for the caller and the program can be freed, while apc->bpf_prog
still points at it. The next consumer of mana_xdp_get() - typically
mana_chn_setxdp() from mana_alloc_queues() on the following ifup, or
after a TX timeout reset - then calls bpf_prog_add() on freed memory.

[...]

Here is the summary with links:
  - [net] net: mana: restore the XDP program pointer when pre-allocation fails
    https://git.kernel.org/netdev/net/c/4c46beb807ef

You are awesome, thank you!
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