RDMA/ucma: Protect mc during concurrent multicast leaves

Partially revert the commit mentioned in the Fixes line to make sure that
allocation and erasing multicast struct are locked.

  BUG: KASAN: use-after-free in ucma_cleanup_multicast drivers/infiniband/core/ucma.c:491 [inline]
  BUG: KASAN: use-after-free in ucma_destroy_private_ctx+0x914/0xb70 drivers/infiniband/core/ucma.c:579
  Read of size 8 at addr ffff88801bb74b00 by task syz-executor.1/25529
  CPU: 0 PID: 25529 Comm: syz-executor.1 Not tainted 5.16.0-rc7-syzkaller #0
  Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
  Call Trace:
   __dump_stack lib/dump_stack.c:88 [inline]
   dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
   print_address_description.constprop.0.cold+0x8d/0x320 mm/kasan/report.c:247
   __kasan_report mm/kasan/report.c:433 [inline]
   kasan_report.cold+0x83/0xdf mm/kasan/report.c:450
   ucma_cleanup_multicast drivers/infiniband/core/ucma.c:491 [inline]
   ucma_destroy_private_ctx+0x914/0xb70 drivers/infiniband/core/ucma.c:579
   ucma_destroy_id+0x1e6/0x280 drivers/infiniband/core/ucma.c:614
   ucma_write+0x25c/0x350 drivers/infiniband/core/ucma.c:1732
   vfs_write+0x28e/0xae0 fs/read_write.c:588
   ksys_write+0x1ee/0x250 fs/read_write.c:643
   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
   do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
   entry_SYSCALL_64_after_hwframe+0x44/0xae

Currently the xarray search can touch a concurrently freeing mc as the
xa_for_each() is not surrounded by any lock. Rather than hold the lock for
a full scan hold it only for the effected items, which is usually an empty
list.

Fixes: 95fe510 ("RDMA/ucma: Remove mc_list and rely on xarray")
Link: https://lore.kernel.org/r/1cda5fabb1081e8d16e39a48d3a4f8160cea88b8.1642491047.git.leonro@nvidia.com
Reported-by: syzbot+e3f96c43d19782dd14a7@syzkaller.appspotmail.com
Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Maor Gottlieb <maorg@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/core/ucma.c

@@ -95,6 +95,7 @@ struct ucma_context {
 	u64			uid;
 
 	struct list_head	list;
+	struct list_head	mc_list;
 	struct work_struct	close_work;
 };
 
@@ -105,6 +106,7 @@ struct ucma_multicast {
 
 	u64			uid;
 	u8			join_state;
+	struct list_head	list;
 	struct sockaddr_storage	addr;
 };
 
@@ -198,6 +200,7 @@ static struct ucma_context *ucma_alloc_ctx(struct ucma_file *file)
 
 	INIT_WORK(&ctx->close_work, ucma_close_id);
 	init_completion(&ctx->comp);
+	INIT_LIST_HEAD(&ctx->mc_list);
 	/* So list_del() will work if we don't do ucma_finish_ctx() */
 	INIT_LIST_HEAD(&ctx->list);
 	ctx->file = file;
@@ -484,19 +487,19 @@ static ssize_t ucma_create_id(struct ucma_file *file, const char __user *inbuf,
 
 static void ucma_cleanup_multicast(struct ucma_context *ctx)
 {
-	struct ucma_multicast *mc;
-	unsigned long index;
+	struct ucma_multicast *mc, *tmp;
 
-	xa_for_each(&multicast_table, index, mc) {
-		if (mc->ctx != ctx)
-			continue;
+	xa_lock(&multicast_table);
+	list_for_each_entry_safe(mc, tmp, &ctx->mc_list, list) {
+		list_del(&mc->list);
 		/*
 		 * At this point mc->ctx->ref is 0 so the mc cannot leave the
 		 * lock on the reader and this is enough serialization
 		 */
-		xa_erase(&multicast_table, index);
+		__xa_erase(&multicast_table, mc->id);
 		kfree(mc);
 	}
+	xa_unlock(&multicast_table);
 }
 
 static void ucma_cleanup_mc_events(struct ucma_multicast *mc)
@@ -1469,12 +1472,16 @@ static ssize_t ucma_process_join(struct ucma_file *file,
 	mc->uid = cmd->uid;
 	memcpy(&mc->addr, addr, cmd->addr_size);
 
-	if (xa_alloc(&multicast_table, &mc->id, NULL, xa_limit_32b,
+	xa_lock(&multicast_table);
+	if (__xa_alloc(&multicast_table, &mc->id, NULL, xa_limit_32b,
 		     GFP_KERNEL)) {
 		ret = -ENOMEM;
 		goto err_free_mc;
 	}
 
+	list_add_tail(&mc->list, &ctx->mc_list);
+	xa_unlock(&multicast_table);
+
 	mutex_lock(&ctx->mutex);
 	ret = rdma_join_multicast(ctx->cm_id, (struct sockaddr *)&mc->addr,
 				  join_state, mc);
@@ -1500,8 +1507,11 @@ static ssize_t ucma_process_join(struct ucma_file *file,
 	mutex_unlock(&ctx->mutex);
 	ucma_cleanup_mc_events(mc);
 err_xa_erase:
-	xa_erase(&multicast_table, mc->id);
+	xa_lock(&multicast_table);
+	list_del(&mc->list);
+	__xa_erase(&multicast_table, mc->id);
 err_free_mc:
+	xa_unlock(&multicast_table);
 	kfree(mc);
 err_put_ctx:
 	ucma_put_ctx(ctx);
@@ -1569,15 +1579,17 @@ static ssize_t ucma_leave_multicast(struct ucma_file *file,
 		mc = ERR_PTR(-EINVAL);
 	else if (!refcount_inc_not_zero(&mc->ctx->ref))
 		mc = ERR_PTR(-ENXIO);
-	else
-		__xa_erase(&multicast_table, mc->id);
-	xa_unlock(&multicast_table);
 
 	if (IS_ERR(mc)) {
+		xa_unlock(&multicast_table);
 		ret = PTR_ERR(mc);
 		goto out;
 	}
 
+	list_del(&mc->list);
+	__xa_erase(&multicast_table, mc->id);
+	xa_unlock(&multicast_table);
+
 	mutex_lock(&mc->ctx->mutex);
 	rdma_leave_multicast(mc->ctx->cm_id, (struct sockaddr *) &mc->addr);
 	mutex_unlock(&mc->ctx->mutex);