net: fix a memleak when uncloning an skb dst and its metadata

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: net: fix a memleak when uncloning an skb dst and its metadata When uncloning an skb dst and its associated metadata, a new dst+metadata is allocated and later replaces the old one in the skb. This is helpful to have a non-shared dst+metadata attached to a specific skb. The issue is the uncloned dst+metadata is initialized with a refcount of 1, which is increased to 2 before attaching it to the skb. When tun_dst_unclone returns, the dst+metadata is only referenced from a single place (the skb) while its refcount is 2. Its refcount will never drop to 0 (when the skb is consumed), leading to a memory leak. Fix this by removing the call to dst_hold in tun_dst_unclone, as the dst+metadata refcount is already 1.

References

• https://git.kernel.org/stable/c/4ac84498fbe84a00e7aef185e2bb3e40ce71eca4
• https://git.kernel.org/stable/c/c1ff27d100e2670b03cbfddb9117e5f9fc672540
• https://git.kernel.org/stable/c/0be943916d781df2b652793bb2d3ae4f9624c10a
• https://git.kernel.org/stable/c/a80817adc2a4c1ba26a7aa5f3ed886e4a18dff88
• https://git.kernel.org/stable/c/00e6d6c3bc14dfe32824e2c515f0e0f2d6ecf2f1
• https://git.kernel.org/stable/c/fdcb263fa5cda15b8cb24a641fa2718c47605314
• https://git.kernel.org/stable/c/8b1087b998e273f07be13dcb5f3ca4c309c7f108
• https://git.kernel.org/stable/c/9eeabdf17fa0ab75381045c867c370f4cc75a613