Forwarded: [PATCH] usb: gadget: inode: keep ep_data alive via the ep inode reference

[syzbot <syzbot+7bf725ed337e37307001@syzkaller.appspotmail.com>]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.

***

Subject: [PATCH] usb: gadget: inode: keep ep_data alive via the ep inode reference
Author: adrianox@gmail.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
---
 drivers/usb/gadget/legacy/inode.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/drivers/usb/gadget/legacy/inode.c b/drivers/usb/gadget/legacy/inode.c
index db961aaa3740..dc0cba86cf30 100644
--- a/drivers/usb/gadget/legacy/inode.c
+++ b/drivers/usb/gadget/legacy/inode.c
@@ -1626,6 +1626,16 @@ static int activate_ep_files (struct dev_data *dev)
 		if (!data->req)
 			goto enomem1;
 
+		/*
+		 * The inode created below references this ep_data through
+		 * ->i_private and gadgetfs_evict_inode() releases it again.
+		 * Without this the inode could outlive the ep_data and a
+		 * concurrent openat() -> ep_open() would dereference freed
+		 * memory (reported as a slab-use-after-free in the mutex fast
+		 * path).  Keep the object alive for as long as any inode points
+		 * to it.
+		 */
+		get_ep(data);
 		err = gadgetfs_create_file (dev->sb, data->name,
 				data, &ep_io_operations);
 		if (err)
@@ -2015,9 +2025,25 @@ static int gadgetfs_create_file (struct super_block *sb, char const *name,
 	return 0;
 }
 
+static void gadgetfs_evict_inode(struct inode *inode)
+{
+	/*
+	 * EP file inodes keep their struct ep_data alive through ->i_private;
+	 * drop that reference when the inode finally goes away.  This closes
+	 * the ep_open() vs. gadgetfs_unbind()/destroy_ep_files() race where
+	 * the ep_data was freed while an inode still pointed to it.
+	 */
+	if (inode->i_fop == &ep_io_operations)
+		put_ep(inode->i_private);
+
+	truncate_inode_pages_final(&inode->i_data);
+	clear_inode(inode);
+}
+
 static const struct super_operations gadget_fs_operations = {
 	.statfs =	simple_statfs,
 	.drop_inode =	inode_just_drop,
+	.evict_inode =	gadgetfs_evict_inode,
 };
 
 static int
-- 
2.51.0