io_uring: fix physical SQE bounds check for SQE_MIXED 128-byte ops

In the Linux kernel, the following vulnerability has been resolved:

io_uring: fix physical SQE bounds check for SQE_MIXED 128-byte ops

When IORING_SETUP_SQE_MIXED is used without IORING_SETUP_NO_SQARRAY,

the boundary check for 128-byte SQE operations in io_init_req()

validated the logical SQ head position rather than the physical SQE

index.

The existing check:

!(ctx->cached_sq_head & (ctx->sq_entries - 1))

ensures the logical position isn't at the end of the ring, which is

correct for NO_SQARRAY rings where physical == logical. However, when

sq_array is present, an unprivileged user can remap any logical

position to an arbitrary physical index via sq_array. Setting

sq_array[N] = sq_entries - 1 places a 128-byte operation at the last

physical SQE slot, causing the 128-byte memcpy in

io_uring_cmd_sqe_copy() to read 64 bytes past the end of the SQE

array.

Replace the cached_sq_head alignment check with a direct validation

of the physical SQE index, which correctly handles both sq_array and

NO_SQARRAY cases.