On 08/03/2021 14:16, Pavel Begunkov wrote:
> From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
>
> You can't call idr_remove() from within a idr_for_each() callback,
> but you can call xa_erase() from an xa_for_each() loop, so switch the
> entire personality_idr from the IDR to the XArray. This manifests as a
> use-after-free as idr_for_each() attempts to walk the rest of the node
> after removing the last entry from it.
yangerkun, can you test it and similarly take care of buffer idr?
>
> Fixes: 071698e13ac6 ("io_uring: allow registering credentials")
> Cc: stable@xxxxxxxxxxxxxxx # 5.6+
> Reported-by: yangerkun <yangerkun@xxxxxxxxxx>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> [Pavel: rebased (creds load was moved into io_init_req())]
> Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
> ---
> fs/io_uring.c | 47 ++++++++++++++++++++++++-----------------------
> 1 file changed, 24 insertions(+), 23 deletions(-)
>
> p.s. passes liburing tests well
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 5ef9f836cccc..5505e19f1391 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -407,7 +407,8 @@ struct io_ring_ctx {
>
> struct idr io_buffer_idr;
>
> - struct idr personality_idr;
> + struct xarray personalities;
> + u32 pers_next;
>
> struct {
> unsigned cached_cq_tail;
> @@ -1138,7 +1139,7 @@ static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
> init_completion(&ctx->ref_comp);
> init_completion(&ctx->sq_thread_comp);
> idr_init(&ctx->io_buffer_idr);
> - idr_init(&ctx->personality_idr);
> + xa_init_flags(&ctx->personalities, XA_FLAGS_ALLOC1);
> mutex_init(&ctx->uring_lock);
> init_waitqueue_head(&ctx->wait);
> spin_lock_init(&ctx->completion_lock);
> @@ -6338,7 +6339,7 @@ static int io_init_req(struct io_ring_ctx *ctx, struct io_kiocb *req,
> req->work.list.next = NULL;
> personality = READ_ONCE(sqe->personality);
> if (personality) {
> - req->work.creds = idr_find(&ctx->personality_idr, personality);
> + req->work.creds = xa_load(&ctx->personalities, personality);
> if (!req->work.creds)
> return -EINVAL;
> get_cred(req->work.creds);
> @@ -8359,7 +8360,6 @@ static void io_ring_ctx_free(struct io_ring_ctx *ctx)
> mutex_unlock(&ctx->uring_lock);
> io_eventfd_unregister(ctx);
> io_destroy_buffers(ctx);
> - idr_destroy(&ctx->personality_idr);
>
> #if defined(CONFIG_UNIX)
> if (ctx->ring_sock) {
> @@ -8424,7 +8424,7 @@ static int io_unregister_personality(struct io_ring_ctx *ctx, unsigned id)
> {
> const struct cred *creds;
>
> - creds = idr_remove(&ctx->personality_idr, id);
> + creds = xa_erase(&ctx->personalities, id);
> if (creds) {
> put_cred(creds);
> return 0;
> @@ -8433,14 +8433,6 @@ static int io_unregister_personality(struct io_ring_ctx *ctx, unsigned id)
> return -EINVAL;
> }
>
> -static int io_remove_personalities(int id, void *p, void *data)
> -{
> - struct io_ring_ctx *ctx = data;
> -
> - io_unregister_personality(ctx, id);
> - return 0;
> -}
> -
> static bool io_run_ctx_fallback(struct io_ring_ctx *ctx)
> {
> struct callback_head *work, *next;
> @@ -8530,13 +8522,17 @@ static void io_ring_exit_work(struct work_struct *work)
>
> static void io_ring_ctx_wait_and_kill(struct io_ring_ctx *ctx)
> {
> + unsigned long index;
> + struct creds *creds;
> +
> mutex_lock(&ctx->uring_lock);
> percpu_ref_kill(&ctx->refs);
> /* if force is set, the ring is going away. always drop after that */
> ctx->cq_overflow_flushed = 1;
> if (ctx->rings)
> __io_cqring_overflow_flush(ctx, true, NULL, NULL);
> - idr_for_each(&ctx->personality_idr, io_remove_personalities, ctx);
> + xa_for_each(&ctx->personalities, index, creds)
> + io_unregister_personality(ctx, index);
> mutex_unlock(&ctx->uring_lock);
>
> io_kill_timeouts(ctx, NULL, NULL);
> @@ -9166,10 +9162,9 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
> }
>
> #ifdef CONFIG_PROC_FS
> -static int io_uring_show_cred(int id, void *p, void *data)
> +static int io_uring_show_cred(struct seq_file *m, unsigned int id,
> + const struct cred *cred)
> {
> - const struct cred *cred = p;
> - struct seq_file *m = data;
> struct user_namespace *uns = seq_user_ns(m);
> struct group_info *gi;
> kernel_cap_t cap;
> @@ -9237,9 +9232,13 @@ static void __io_uring_show_fdinfo(struct io_ring_ctx *ctx, struct seq_file *m)
> seq_printf(m, "%5u: 0x%llx/%u\n", i, buf->ubuf,
> (unsigned int) buf->len);
> }
> - if (has_lock && !idr_is_empty(&ctx->personality_idr)) {
> + if (has_lock && !xa_empty(&ctx->personalities)) {
> + unsigned long index;
> + const struct cred *cred;
> +
> seq_printf(m, "Personalities:\n");
> - idr_for_each(&ctx->personality_idr, io_uring_show_cred, m);
> + xa_for_each(&ctx->personalities, index, cred)
> + io_uring_show_cred(m, index, cred);
> }
> seq_printf(m, "PollList:\n");
> spin_lock_irq(&ctx->completion_lock);
> @@ -9568,14 +9567,16 @@ static int io_probe(struct io_ring_ctx *ctx, void __user *arg, unsigned nr_args)
> static int io_register_personality(struct io_ring_ctx *ctx)
> {
> const struct cred *creds;
> + u32 id;
> int ret;
>
> creds = get_current_cred();
>
> - ret = idr_alloc_cyclic(&ctx->personality_idr, (void *) creds, 1,
> - USHRT_MAX, GFP_KERNEL);
> - if (ret < 0)
> - put_cred(creds);
> + ret = xa_alloc_cyclic(&ctx->personalities, &id, (void *)creds,
> + XA_LIMIT(0, USHRT_MAX), &ctx->pers_next, GFP_KERNEL);
> + if (!ret)
> + return id;
> + put_cred(creds);
> return ret;
> }
>
>
--
Pavel Begunkov
