nvmet-auth: assign dh_key to NULL after kfree_sensitive

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: nvmet-auth: assign dh_key to NULL after kfree_sensitive ctrl->dh_key might be used across multiple calls to nvmet_setup_dhgroup() for the same controller. So it's better to nullify it after release on error path in order to avoid double free later in nvmet_destroy_auth(). Found by Linux Verification Center (linuxtesting.org) with Svace.

References

• https://git.kernel.org/stable/c/c94e965f766321641ec38e4eece9ce8884543244
• https://git.kernel.org/stable/c/c60af16e1d6cc2237d58336546d6adfc067b6b8f
• https://git.kernel.org/stable/c/e61bd51e44409495d75847e9230736593e4c8710
• https://git.kernel.org/stable/c/d2f551b1f72b4c508ab9298419f6feadc3b5d791