io_uring/fdinfo: fix OOB read in SQE_MIXED wrap check

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

io_uring/fdinfo: fix OOB read in SQE_MIXED wrap check

__io_uring_show_fdinfo() iterates over pending SQEs and, for 128-byte

SQEs on an IORING_SETUP_SQE_MIXED ring, needs to detect when the second

half of the SQE would be past the end of the sq_sqes array. The current

check tests (++sq_head & sq_mask) == 0, but sq_head is only incremented

when a 128-byte SQE is encountered, not on every iteration. The actual

array index is sq_idx = (i + sq_head) & sq_mask, which can be sq_mask

(the last slot) while the wrap check passes.

Fix by checking sq_idx directly. Keep the sq_head increment so the loop

still skips the second half of the 128-byte SQE on the next iteration.