From: "Matthew Wilcox (Oracle)" willy@infradead.org

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.

Fixes: 071698e13ac6 ("io_uring: allow registering credentials") Cc: stable@vger.kernel.org # 5.6+ Reported-by: yangerkun yangerkun@huawei.com Signed-off-by: Matthew Wilcox (Oracle) willy@infradead.org [Pavel: rebased (creds load was moved into io_init_req())] Signed-off-by: Pavel Begunkov asml.silence@gmail.com Link: https://lore.kernel.org/r/7ccff36e1375f2b0ebf73d957f037b43becc0dde.161521280... Signed-off-by: Jens Axboe axboe@kernel.dk --- fs/io_uring.c | 47 ++++++++++++++++++++++++----------------------- 1 file changed, 24 insertions(+), 23 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c index 3f6db813d670..84eb499368a4 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -406,7 +406,8 @@ struct io_ring_ctx {

struct idr io_buffer_idr;

- struct idr personality_idr; + struct xarray personalities; + u32 pers_next;

struct { unsigned cached_cq_tail; @@ -1137,7 +1138,7 @@ 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); @@ -6337,7 +6338,7 @@ 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); @@ -8355,7 +8356,6 @@ 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) { @@ -8420,7 +8420,7 @@ 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; @@ -8429,14 +8429,6 @@ 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; @@ -8526,13 +8518,17 @@ 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); @@ -9162,10 +9158,9 @@ 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; @@ -9233,9 +9228,13 @@ 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); @@ -9564,14 +9563,16 @@ 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; }