CVE-2021-3491

The io_uring subsystem in the Linux kernel allowed the MAX_RW_COUNT limit
to be bypassed in the PROVIDE_BUFFERS operation, which led to negative
values being usedin mem_rw when reading /proc/<PID>/mem. This could be used
to create a heap overflow leading to arbitrary code execution in the
kernel. It was addressed via commit d1f82808877b (“io_uring: truncate
lengths larger than MAX_RW_COUNT on provide buffers”) (v5.13-rc1) and
backported to the stable kernels in v5.12.4, v5.11.21, and v5.10.37. It was
introduced in ddf0322db79c (“io_uring: add IORING_OP_PROVIDE_BUFFERS”)
(v5.7-rc1).