Re: [PATCH] io_uring: fix shift-out-of-bounds when round up cq size

[Jens Axboe <axboe@kernel.dk>]

On 11/24/20 12:03 AM, Joseph Qi wrote:
> Abaci Fuzz reported a shift-out-of-bounds BUG in io_uring_create():
> 
> [ 59.598207] UBSAN: shift-out-of-bounds in ./include/linux/log2.h:57:13
> [ 59.599665] shift exponent 64 is too large for 64-bit type 'long unsigned int'
> [ 59.601230] CPU: 0 PID: 963 Comm: a.out Not tainted 5.10.0-rc4+ #3
> [ 59.602502] Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
> [ 59.603673] Call Trace:
> [ 59.604286] dump_stack+0x107/0x163
> [ 59.605237] ubsan_epilogue+0xb/0x5a
> [ 59.606094] __ubsan_handle_shift_out_of_bounds.cold+0xb2/0x20e
> [ 59.607335] ? lock_downgrade+0x6c0/0x6c0
> [ 59.608182] ? rcu_read_lock_sched_held+0xaf/0xe0
> [ 59.609166] io_uring_create.cold+0x99/0x149
> [ 59.610114] io_uring_setup+0xd6/0x140
> [ 59.610975] ? io_uring_create+0x2510/0x2510
> [ 59.611945] ? lockdep_hardirqs_on_prepare+0x286/0x400
> [ 59.613007] ? syscall_enter_from_user_mode+0x27/0x80
> [ 59.614038] ? trace_hardirqs_on+0x5b/0x180
> [ 59.615056] do_syscall_64+0x2d/0x40
> [ 59.615940] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> [ 59.617007] RIP: 0033:0x7f2bb8a0b239
> 
> This is caused by roundup_pow_of_two() if the input entries larger
> enough, e.g. 2^32-1. For sq_entries, it will check first and we allow
> at most IORING_MAX_ENTRIES, so it is okay. But for cq_entries, we do
> round up first, that may overflow and truncate it to 0, which is not
> the expected behavior. So check the cq size first and then do round up.

Applied, thanks.

-- 
Jens Axboe