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    SubjectRe: [syzbot] [net?] KASAN: use-after-free Read in __skb_flow_dissect (3)
    Date
    On Mon, 01 Jan 2024 09:18:16 -0800
    > syzbot found the following issue on:
    >
    > HEAD commit: f5837722ffec Merge tag 'mm-hotfixes-stable-2023-12-27-15-0..
    > git tree: upstream
    > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=122dfc65e80000

    #syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

    --- x/net/core/filter.c
    +++ y/net/core/filter.c
    @@ -2144,6 +2144,7 @@ static int __bpf_redirect_no_mac(struct
    unsigned int mlen = skb_network_offset(skb);

    if (unlikely(skb->len <= mlen)) {
    +out:
    kfree_skb(skb);
    return -ERANGE;
    }
    @@ -2159,6 +2160,8 @@ static int __bpf_redirect_no_mac(struct
    if (!skb_at_tc_ingress(skb))
    skb_postpull_rcsum(skb, skb_mac_header(skb), mlen);
    }
    + if (skb->len <= sizeof(struct iphdr))
    + goto out;
    skb_pop_mac_header(skb);
    skb_reset_mac_len(skb);
    return flags & BPF_F_INGRESS ?
    @@ -2431,7 +2434,7 @@ enum {
    BPF_CALL_3(bpf_clone_redirect, struct sk_buff *, skb, u32, ifindex, u64, flags)
    {
    struct net_device *dev;
    - struct sk_buff *clone;
    + struct sk_buff *buf;
    int ret;

    if (unlikely(flags & (~(BPF_F_INGRESS) | BPF_F_REDIRECT_INTERNAL)))
    @@ -2441,22 +2444,11 @@ BPF_CALL_3(bpf_clone_redirect, struct sk
    if (unlikely(!dev))
    return -EINVAL;

    - clone = skb_clone(skb, GFP_ATOMIC);
    - if (unlikely(!clone))
    + buf = skb_copy(skb, GFP_ATOMIC);
    + if (unlikely(!buf))
    return -ENOMEM;

    - /* For direct write, we need to keep the invariant that the skbs
    - * we're dealing with need to be uncloned. Should uncloning fail
    - * here, we need to free the just generated clone to unclone once
    - * again.
    - */
    - ret = bpf_try_make_head_writable(skb);
    - if (unlikely(ret)) {
    - kfree_skb(clone);
    - return -ENOMEM;
    - }
    -
    - return __bpf_redirect(clone, dev, flags);
    + return __bpf_redirect(buf, dev, flags);
    }

    static const struct bpf_func_proto bpf_clone_redirect_proto = {
    --
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