atm: clip: Fix memory leak of struct clip_vcc.

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: atm: clip: Fix memory leak of struct clip_vcc. ioctl(ATMARP_MKIP) allocates struct clip_vcc and set it to vcc->user_back. The code assumes that vcc_destroy_socket() passes NULL skb to vcc->push() when the socket is close()d, and then clip_push() frees clip_vcc. However, ioctl(ATMARPD_CTRL) sets NULL to vcc->push() in atm_init_atmarp(), resulting in memory leak. Let's serialise two ioctl() by lock_sock() and check vcc->push() in atm_init_atmarp() to prevent memleak.

References

• https://git.kernel.org/stable/c/2fb37ab3226606cbfc9b2b6f9e301b0b735734c5
• https://git.kernel.org/stable/c/9e4dbeee56f614e3f1e166e5d0655a999ea185ef
• https://git.kernel.org/stable/c/1c075e88d5859a2c6b43b27e0e46fb281cef8039
• https://git.kernel.org/stable/c/0c17ff462d98c997d707ee5cf4e4a9b1b52b9d90
• https://git.kernel.org/stable/c/1fb9fb5a4b5cec2d56e26525ef8c519de858fa60
• https://git.kernel.org/stable/c/9f771816f14da6d6157a8c30069091abf6b566fb
• https://git.kernel.org/stable/c/cb2e4a2f8f268d8fba6662f663a2e57846f14a8d
• https://git.kernel.org/stable/c/62dba28275a9a3104d4e33595c7b3328d4032d8d