net: tipc: fix refcount warning in tipc_aead_encrypt

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: net: tipc: fix refcount warning in tipc_aead_encrypt syzbot reported a refcount warning [1] caused by calling get_net() on a network namespace that is being destroyed (refcount=0). This happens when a TIPC discovery timer fires during network namespace cleanup. The recently added get_net() call in commit e279024617134 ("net/tipc: fix slab-use-after-free Read in tipc_aead_encrypt_done") attempts to hold a reference to the network namespace. However, if the namespace is already being destroyed, its refcount might be zero, leading to the use-after-free warning. Replace get_net() with maybe_get_net(), which safely checks if the refcount is non-zero before incrementing it. If the namespace is being destroyed, return -ENODEV early, after releasing the bearer reference. [1]: https://lore.kernel.org/all/68342b55.a70a0220.253bc2.0091.GAE@google.com/T/#m12019cf9ae77e1954f666914640efa36d52704a2

References

• https://git.kernel.org/stable/c/445d59025d76d0638b03110f8791d5b89ed5162d
• https://git.kernel.org/stable/c/e0b11227c4e8eb4bdf1b86aa8f0f3abb24e0f029
• https://git.kernel.org/stable/c/307391e8fe70401a6d39ecc9978e13c2c0cdf81f
• https://git.kernel.org/stable/c/acab7ca5ff19889b80a8ee7dec220ee1a96dede9
• https://git.kernel.org/stable/c/c762fc79d710d676b793f9d98b1414efe6eb51e6
• https://git.kernel.org/stable/c/9ff60e0d9974dccf24e89bcd3ee7933e538d929f
• https://git.kernel.org/stable/c/f29ccaa07cf3d35990f4d25028cc55470d29372b