[PATCH v2 2/4] usb: gadget: f_fs: Tie read_buffer lifetime to ffs_epfile

[Neill Kapron <nkapron@google.com>]

Currently, ffs_epfile_release unconditionally frees the endpoint's
read_buffer when a file descriptor is closed. If userspace explicitly
opens the endpoint multiple times and closes one, the read_buffer is
destroyed. This can lead to silent data loss if other file descriptors
are still actively reading from the endpoint.

By tying the lifetime of the read_buffer to the ffs_epfile structure itself
(which is destroyed when the functionfs instance is torn down in
ffs_epfiles_destroy), we eliminate the brittle dependency on open/release
calls while correctly matching the conceptual lifetime of unread data on
the hardware endpoint.

Fixes: 9353afbbfa7b ("usb: gadget: f_fs: buffer data from ‘oversized’ OUT requests")
Cc: stable@vger.kernel.org
Assisted-by: Antigravity:gemini-3.1-pro
Signed-off-by: Neill Kapron <nkapron@google.com>
---
 drivers/usb/gadget/function/f_fs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index 38e36faefe92..374ab36eaaa3 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -1374,7 +1374,6 @@ ffs_epfile_release(struct inode *inode, struct file *file)
 
 	mutex_unlock(&epfile->dmabufs_mutex);
 
-	__ffs_epfile_read_buffer_free(epfile);
 	ffs_data_closed(epfile->ffs);
 
 	return 0;
@@ -2390,6 +2389,7 @@ static void ffs_epfiles_destroy(struct super_block *sb,
 
 	for (; count; --count, ++epfile) {
 		BUG_ON(mutex_is_locked(&epfile->mutex));
+		__ffs_epfile_read_buffer_free(epfile);
 		simple_remove_by_name(root, epfile->name, clear_one);
 	}
 
-- 
2.54.0.1136.gdb2ca164c4-goog