io_uring: Convert personality_idr to XArray

commit 61cf93700fe6359552848ed5e3becba6cd760efa upstream.

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.1615212806.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Hanjun Guo <guohanjun@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 0cbf2a0..cd93bf5 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -346,7 +346,8 @@ struct io_ring_ctx {
 
        struct idr              io_buffer_idr;
 
-       struct idr              personality_idr;
+       struct xarray           personalities;
+       u32                     pers_next;
 
        struct {
                unsigned                cached_cq_tail;
@@ -1212,7 +1213,7 @@ 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);
@@ -6629,7 +6630,7 @@ static int io_init_req(struct io_ring_ctx *ctx, struct io_kiocb *req,
        if (id) {
                struct io_identity *iod;
 
-               iod = idr_find(&ctx->personality_idr, id);
+               iod = xa_load(&ctx->personalities, id);
                if (unlikely(!iod))
                        return -EINVAL;
                refcount_inc(&iod->count);
@@ -8445,7 +8446,6 @@ static void io_ring_ctx_free(struct io_ring_ctx *ctx)
        io_sqe_files_unregister(ctx);
        io_eventfd_unregister(ctx);
        io_destroy_buffers(ctx);
-       idr_destroy(&ctx->personality_idr);
 
 #if defined(CONFIG_UNIX)
        if (ctx->ring_sock) {
@@ -8509,7 +8509,7 @@ static int io_unregister_personality(struct io_ring_ctx *ctx, unsigned id)
 {
        struct io_identity *iod;
 
-       iod = idr_remove(&ctx->personality_idr, id);
+       iod = xa_erase(&ctx->personalities, id);
        if (iod) {
                put_cred(iod->creds);
                if (refcount_dec_and_test(&iod->count))
@@ -8520,14 +8520,6 @@ 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 void io_ring_exit_work(struct work_struct *work)
 {
        struct io_ring_ctx *ctx = container_of(work, struct io_ring_ctx,
@@ -8554,6 +8546,9 @@ static bool io_cancel_ctx_cb(struct io_wq_work *work, void *data)
 
 static void io_ring_ctx_wait_and_kill(struct io_ring_ctx *ctx)
 {
+       unsigned long index;
+       struct io_identify *iod;
+
        mutex_lock(&ctx->uring_lock);
        percpu_ref_kill(&ctx->refs);
        /* if force is set, the ring is going away. always drop after that */
@@ -8574,7 +8569,8 @@ static void io_ring_ctx_wait_and_kill(struct io_ring_ctx *ctx)
 
        /* if we failed setting up the ctx, we might not have any rings */
        io_iopoll_try_reap_events(ctx);
-       idr_for_each(&ctx->personality_idr, io_remove_personalities, ctx);
+       xa_for_each(&ctx->personalities, index, iod)
+                io_unregister_personality(ctx, index);
 
        /*
         * Do this upfront, so we won't have a grace period where the ring
@@ -9137,11 +9133,10 @@ out_fput:
 }
 
 #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 io_identity *iod)
 {
-       struct io_identity *iod = p;
        const struct cred *cred = iod->creds;
-       struct seq_file *m = data;
        struct user_namespace *uns = seq_user_ns(m);
        struct group_info *gi;
        kernel_cap_t cap;
@@ -9209,9 +9204,13 @@ 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 io_identity *iod;
+
                seq_printf(m, "Personalities:\n");
-               idr_for_each(&ctx->personality_idr, io_uring_show_cred, m);
+               xa_for_each(&ctx->personalities, index, iod)
+                       io_uring_show_cred(m, index, iod);
        }
        seq_printf(m, "PollList:\n");
        spin_lock_irq(&ctx->completion_lock);
@@ -9597,21 +9596,23 @@ out:
 
 static int io_register_personality(struct io_ring_ctx *ctx)
 {
-       struct io_identity *id;
+       struct io_identity *iod;
+       u32 id;
        int ret;
 
-       id = kmalloc(sizeof(*id), GFP_KERNEL);
-       if (unlikely(!id))
+       iod = kmalloc(sizeof(*iod), GFP_KERNEL);
+       if (unlikely(!iod))
                return -ENOMEM;
 
-       io_init_identity(id);
-       id->creds = get_current_cred();
+       io_init_identity(iod);
+       iod->creds = get_current_cred();
 
-       ret = idr_alloc_cyclic(&ctx->personality_idr, id, 1, USHRT_MAX, GFP_KERNEL);
-       if (ret < 0) {
-               put_cred(id->creds);
-               kfree(id);
-       }
+       ret = xa_alloc_cyclic(&ctx->personalities, &id, (void *)iod,
+                       XA_LIMIT(0, USHRT_MAX), &ctx->pers_next, GFP_KERNEL);
+       if (!ret)
+               return id;
+       put_cred(iod->creds);
+       kfree(iod);
        return ret;
 }