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io_uring: prevent racy sqd->thread checks 

SQPOLL thread to which we're trying to attach may be going away, it's
not nice but a more serious problem is if io_sq_offload_create() sees
sqd->thread==NULL, and tries to init it with a new thread. There are
tons of ways it can be exploited or fail.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Pavel Begunkov 2021-03-11 23:29:37 +00:00 committed by Jens Axboe
parent 0df8ea602b
commit 26984fbf3a
1 changed files with 22 additions and 6 deletions
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28
fs/io_uring.c
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@ -7119,14 +7119,18 @@ static struct io_sq_data *io_attach_sq_data(struct io_uring_params *p)
return sqd;
}
static struct io_sq_data *io_get_sq_data(struct io_uring_params *p)
static struct io_sq_data *io_get_sq_data(struct io_uring_params *p,
bool *attached)
{
struct io_sq_data *sqd;
*attached = false;
if (p->flags & IORING_SETUP_ATTACH_WQ) {
sqd = io_attach_sq_data(p);
if (!IS_ERR(sqd))
if (!IS_ERR(sqd)) {
*attached = true;
return sqd;
}
/* fall through for EPERM case, setup new sqd/task */
if (PTR_ERR(sqd) != -EPERM)
return sqd;
@ -7799,12 +7803,13 @@ static int io_sq_offload_create(struct io_ring_ctx *ctx,
if (ctx->flags & IORING_SETUP_SQPOLL) {
struct task_struct *tsk;
struct io_sq_data *sqd;
bool attached;
ret = -EPERM;
if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_NICE))
goto err;
sqd = io_get_sq_data(p);
sqd = io_get_sq_data(p, &attached);
if (IS_ERR(sqd)) {
ret = PTR_ERR(sqd);
goto err;
@ -7816,13 +7821,24 @@ static int io_sq_offload_create(struct io_ring_ctx *ctx,
if (!ctx->sq_thread_idle)
ctx->sq_thread_idle = HZ;
ret = 0;
io_sq_thread_park(sqd);
list_add(&ctx->sqd_list, &sqd->ctx_list);
io_sqd_update_thread_idle(sqd);
/* don't attach to a dying SQPOLL thread, would be racy */
if (attached && !sqd->thread) {
ret = -ENXIO;
} else {
list_add(&ctx->sqd_list, &sqd->ctx_list);
io_sqd_update_thread_idle(sqd);
}
io_sq_thread_unpark(sqd);
if (sqd->thread)
if (ret < 0) {
io_put_sq_data(sqd);
ctx->sq_data = NULL;
return ret;
} else if (attached) {
return 0;
}
if (p->flags & IORING_SETUP_SQ_AFF) {
int cpu = p->sq_thread_cpu;