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HWZHOrhmTBiSUND5nILYFy1XQ0S4iEvy On 2026-05-21 9:44 AM, Weiming Shi wrote: > On 26-05-20 20:58, Willem de Bruijn wrote: >> Dongli Zhang wrote: >>> >>> >>> On 2026-05-20 5:05 PM, Willem de Bruijn wrote: >>>> Weiming Shi wrote: >>>>> tun_xdp_one() returns -EINVAL on a frame shorter than ETH_HLEN without >>>>> freeing the page that vhost_net_build_xdp() allocated for it. >>>>> tun_sendmsg() discards that -EINVAL and still returns total_len, so >>>>> vhost_tx_batch() takes the success path and never frees the page; each >>>>> short frame in a batch leaks one page-frag chunk. >>>>> >>>>> A local process that can open /dev/net/tun and /dev/vhost-net can hit >>>>> this path: it attaches a tun/tap device as the vhost-net backend and >>>>> feeds TX descriptors whose length minus the virtio-net header is below >>>>> ETH_HLEN. Each kick leaks the page-frag chunks for that batch, and a >>>>> tight submission loop exhausts host memory and triggers an OOM panic. >>>>> Free the page before returning -EINVAL, matching the XDP-program error >>>>> path in the same function. >>>>> >>>>> Fixes: 049584807f1d ("tun: add missing verification for short frame") >>>>> Reported-by: Xiang Mei >>>>> Assisted-by: Claude:claude-opus-4-7 >>>>> Signed-off-by: Weiming Shi >>>>> --- >>>>> drivers/net/tun.c | 4 +++- >>>>> 1 file changed, 3 insertions(+), 1 deletion(-) >>>>> >>>>> diff --git a/drivers/net/tun.c b/drivers/net/tun.c >>>>> index b183189f1853..f594360d66d6 100644 >>>>> --- a/drivers/net/tun.c >>>>> +++ b/drivers/net/tun.c >>>>> @@ -2394,8 +2394,10 @@ static int tun_xdp_one(struct tun_struct *tun, >>>>> bool skb_xdp = false; >>>>> struct page *page; >>>>> >>>>> - if (unlikely(datasize < ETH_HLEN)) >>>>> + if (unlikely(datasize < ETH_HLEN)) { >>>>> + put_page(virt_to_head_page(xdp->data)); >>>>> return -EINVAL; >>>>> + } >>>> >>>> Make sense, thanks. >>>> >>>> The error path from tun_xdp_act does the same. And the default: label >>>> used to too, before a batching optimization was introduced. >>>> >>>> Is the same then also missing if build_skb fails? >>>> >>> >>> I also agree that we may need to handle build_skb() failure. >> >> Thanks. Fine to defer to a separate patch btw. Either way. >> >>> In addition, I think we may need this fix for tap_get_user_xdp() as well. >>> >>> Thank you very much! >>> >>> Dongli Zhang >> >> > Hi, > > I have sent a patch to fix the same issue and the patch is under review now. > Please take a look if you have time, thanks! > > https://urldefense.com/v3/__https://lore.kernel.org/all/20260521163230.1478627-2-bestswngs@gmail.com/__;!!ACWV5N9M2RV99hQ!IDJKNE6zGJJ7hjjCFU8OviGWfh4A_mNZAhrTowR0Kb4p5bm4JmoCmEI6_GfOXFjcxd2ctJ3pbcJypErFgC4-$ > https://urldefense.com/v3/__https://lore.kernel.org/all/20260521163312.1479805-2-bestswngs@gmail.com/__;!!ACWV5N9M2RV99hQ!IDJKNE6zGJJ7hjjCFU8OviGWfh4A_mNZAhrTowR0Kb4p5bm4JmoCmEI6_GfOXFjcxd2ctJ3pbcJypMyOq4Op$ > The bug fix applies to both TAP and TUN. TAP has a single patch, while TUN has two separate patches. I'm not sure which approach is better. [PATCH net] tap: free page on error paths in tap_get_user_xdp() https://lore.kernel.org/netdev/20260521163230.1478627-2-bestswngs@gmail.com [PATCH net] tun: free page on short-frame rejection in tun_xdp_one() https://lore.kernel.org/all/20260520160020.375349-2-bestswngs@gmail.com [PATCH net] tun: free page on build_skb failure in tun_xdp_one() https://lore.kernel.org/netdev/20260521163312.1479805-2-bestswngs@gmail.com/ The bug fix looks good to me. Reviewed-by: Dongli Zhang + Michael for FYI regarding vhost as well. Thank you very much! Dongli Zhang