io_uring/fdinfo: grab ctx->uring_lock around io_uring_show_fdinfo()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: io_uring/fdinfo: grab ctx->uring_lock around io_uring_show_fdinfo() Not everything requires locking in there, which is why the 'has_lock' variable exists. But enough does that it's a bit unwieldy to manage. Wrap the whole thing in a ->uring_lock trylock, and just return with no output if we fail to grab it. The existing trylock() will already have greatly diminished utility/output for the failure case. This fixes an issue with reading the SQE fields, if the ring is being actively resized at the same time.

References

• https://git.kernel.org/stable/c/bdb7d2ec2e31c46c45d1f32667dfa8216a72705e
• https://git.kernel.org/stable/c/d871198ee431d90f5308d53998c1ba1d5db5619a
• https://project-zero.issues.chromium.org/issues/417522668