From 044c1ab399afbe9f2ebef49a3204ef1509826dc7 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Mon, 28 Oct 2019 09:15:33 -0600 Subject: [PATCH] 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: 75b28affdd6a ("io_uring: allocate the two rings together") Reported-by: syzbot+6f03d895a6cd0d06187f@syzkaller.appspotmail.com Signed-off-by: Jens Axboe --- fs/io_uring.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/fs/io_uring.c b/fs/io_uring.c index ba1431046c98..c11c4157a4c2 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -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: -- 2.34.1