rxrpc: Fix oops due to non-existence of prealloc backlog struct

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: rxrpc: Fix oops due to non-existence of prealloc backlog struct If an AF_RXRPC service socket is opened and bound, but calls are preallocated, then rxrpc_alloc_incoming_call() will oops because the rxrpc_backlog struct doesn't get allocated until the first preallocation is made. Fix this by returning NULL from rxrpc_alloc_incoming_call() if there is no backlog struct. This will cause the incoming call to be aborted.

References

• https://git.kernel.org/stable/c/bf0ca6a1bc4fb904b598137c6718785a107e3adf
• https://git.kernel.org/stable/c/f7afb3ff01c42c49e8a143cdce400b95844bb506
• https://git.kernel.org/stable/c/f5e72b7824d08c206ce106d30cb37c4642900ccc
• https://git.kernel.org/stable/c/0eef29385d715d4c7fd707b18d4a9b76c76dd5e6
• https://git.kernel.org/stable/c/efc1b2b7c1a308b60df8f36bc2d7ce16d3999364
• https://git.kernel.org/stable/c/d1ff5f9d2c5405681457262e23c720b08977c11f
• https://git.kernel.org/stable/c/2c2e9ebeb036f9b1b09325ec5cfdfe0e78f357c3
• https://git.kernel.org/stable/c/880a88f318cf1d2a0f4c0a7ff7b07e2062b434a4