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SubjectRe: KASAN: use-after-free Read in idr_for_each (2)
On Sun, Nov 29, 2020 at 07:34:29PM +0800, Hillf Danton wrote:
> > radix_tree_next_slot include/linux/radix-tree.h:422 [inline]
> > idr_for_each+0x206/0x220 lib/idr.c:202
> > io_destroy_buffers fs/io_uring.c:8275 [inline]
>
> Matthew, can you shed any light on the link between the use of idr
> routines and the UAF reported?

I presume it's some misuse of IDR by io_uring. I'd rather io_uring
didn't use the IDR at all. This compiles; I promise no more than that.

diff --git a/fs/io_uring.c b/fs/io_uring.c
index ef3cd7fe4416..2fcf196bb3c3 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -344,7 +344,7 @@ struct io_ring_ctx {
struct socket *ring_sock;
#endif

- struct idr io_buffer_idr;
+ struct xarray io_buffers;

struct idr personality_idr;

@@ -1298,7 +1298,7 @@ static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
INIT_LIST_HEAD(&ctx->cq_overflow_list);
init_completion(&ctx->ref_comp);
init_completion(&ctx->sq_thread_comp);
- idr_init(&ctx->io_buffer_idr);
+ xa_init(&ctx->io_buffers);
idr_init(&ctx->personality_idr);
mutex_init(&ctx->uring_lock);
init_waitqueue_head(&ctx->wait);
@@ -3042,7 +3042,7 @@ static struct io_buffer *io_buffer_select(struct io_kiocb *req, size_t *len,

lockdep_assert_held(&req->ctx->uring_lock);

- head = idr_find(&req->ctx->io_buffer_idr, bgid);
+ head = xa_load(&req->ctx->io_buffers, bgid);
if (head) {
if (!list_empty(&head->list)) {
kbuf = list_last_entry(&head->list, struct io_buffer,
@@ -3050,7 +3050,7 @@ static struct io_buffer *io_buffer_select(struct io_kiocb *req, size_t *len,
list_del(&kbuf->list);
} else {
kbuf = head;
- idr_remove(&req->ctx->io_buffer_idr, bgid);
+ xa_erase(&req->ctx->io_buffers, bgid);
}
if (*len > kbuf->len)
*len = kbuf->len;
@@ -4130,7 +4130,8 @@ static int __io_remove_buffers(struct io_ring_ctx *ctx, struct io_buffer *buf,
}
i++;
kfree(buf);
- idr_remove(&ctx->io_buffer_idr, bgid);
+ if (nbufs != -1U)
+ xa_erase(&ctx->io_buffers, bgid);

return i;
}
@@ -4148,7 +4149,7 @@ static int io_remove_buffers(struct io_kiocb *req, bool force_nonblock,
lockdep_assert_held(&ctx->uring_lock);

ret = -ENOENT;
- head = idr_find(&ctx->io_buffer_idr, p->bgid);
+ head = xa_load(&ctx->io_buffers, p->bgid);
if (head)
ret = __io_remove_buffers(ctx, head, p->bgid, p->nbufs);

@@ -4225,15 +4226,15 @@ static int io_provide_buffers(struct io_kiocb *req, bool force_nonblock,

lockdep_assert_held(&ctx->uring_lock);

- list = head = idr_find(&ctx->io_buffer_idr, p->bgid);
+ list = head = xa_load(&ctx->io_buffers, p->bgid);

ret = io_add_buffers(p, &head);
if (ret < 0)
goto out;

if (!list) {
- ret = idr_alloc(&ctx->io_buffer_idr, head, p->bgid, p->bgid + 1,
- GFP_KERNEL);
+ ret = xa_err(xa_store(&ctx->io_buffers, p->bgid, head,
+ GFP_KERNEL));
if (ret < 0) {
__io_remove_buffers(ctx, head, p->bgid, -1U);
goto out;
@@ -8468,19 +8469,15 @@ static int io_eventfd_unregister(struct io_ring_ctx *ctx)
return -ENXIO;
}

-static int __io_destroy_buffers(int id, void *p, void *data)
-{
- struct io_ring_ctx *ctx = data;
- struct io_buffer *buf = p;
-
- __io_remove_buffers(ctx, buf, id, -1U);
- return 0;
-}
-
static void io_destroy_buffers(struct io_ring_ctx *ctx)
{
- idr_for_each(&ctx->io_buffer_idr, __io_destroy_buffers, ctx);
- idr_destroy(&ctx->io_buffer_idr);
+ unsigned long pgid;
+ struct io_buffer *buf;
+
+ xa_for_each(&ctx->io_buffers, pgid, buf) {
+ xa_erase(&ctx->io_buffers, pgid);
+ __io_remove_buffers(ctx, buf, pgid, -1U);
+ }
}

static void io_ring_ctx_free(struct io_ring_ctx *ctx)
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