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Commit 044c1ab3 authored by Jens Axboe's avatar Jens Axboe
Browse files

io_uring: don't touch ctx in setup after ring fd install 



syzkaller reported an issue where it looks like a malicious app can
trigger a use-after-free of reading the ctx ->sq_array and ->rings
value right after having installed the ring fd in the process file
table.

Defer ring fd installation until after we're done reading those
values.

Fixes: 75b28aff ("io_uring: allocate the two rings together")
Reported-by: default avatar <syzbot+6f03d895a6cd0d06187f@syzkaller.appspotmail.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 7b20238d

fs/io_uring.c

+8 −4
Original line number Diff line number Diff line
@@ -3829,10 +3829,6 @@ static int io_uring_create(unsigned entries, struct io_uring_params *p) 
	if (ret)

		goto err;



	ret = io_uring_get_fd(ctx);

	if (ret < 0)

		goto err;



	memset(&p->sq_off, 0, sizeof(p->sq_off));

	p->sq_off.head = offsetof(struct io_rings, sq.head);

	p->sq_off.tail = offsetof(struct io_rings, sq.tail);
@@ -3850,6 +3846,14 @@ static int io_uring_create(unsigned entries, struct io_uring_params *p) 
	p->cq_off.overflow = offsetof(struct io_rings, cq_overflow);

	p->cq_off.cqes = offsetof(struct io_rings, cqes);



	/*

	 * Install ring fd as the very last thing, so we don't risk someone

	 * having closed it before we finish setup

	 */

	ret = io_uring_get_fd(ctx);

	if (ret < 0)

		goto err;



	p->features = IORING_FEAT_SINGLE_MMAP;

	return ret;

err: