CVE-2025-39847

In the Linux kernel, the following vulnerability has been resolved:

ppp: fix memory leak in padcompressskb

If allocskb() fails in padcompress_skb(), it returns NULL without releasing the old skb. The caller does:

skb = pad_compress_skb(ppp, skb);
if (!skb)
    goto drop;

drop: kfree_skb(skb);

When padcompressskb() returns NULL, the reference to the old skb is lost and kfree_skb(skb) ends up doing nothing, leading to a memory leak.

Align padcompressskb() semantics with realloc(): only free the old skb if allocation and compression succeed. At the call site, use the newskb variable so the original skb is not lost when padcompress_skb() fails.