6.6-stable review patch. If anyone has any objections, please let me know.
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From: Victoria Votokina Victoria.Votokina@kaspersky.com
commit 4b1270902609ef0d935ed2faa2ea6d122bd148f5 upstream.
hdm_disconnect() calls most_deregister_interface(), which eventually unregisters the MOST interface device with device_unregister(iface->dev). If that drops the last reference, the device core may call release_mdev() immediately while hdm_disconnect() is still executing.
The old code also freed several mdev-owned allocations in hdm_disconnect() and then performed additional put_device() calls. Depending on refcount order, this could lead to use-after-free or double-free when release_mdev() ran (or when unregister paths also performed puts).
Fix by moving the frees of mdev-owned allocations into release_mdev(), so they happen exactly once when the device is truly released, and by dropping the extra put_device() calls in hdm_disconnect() that are redundant after device_unregister() and most_deregister_interface().
This addresses the KASAN slab-use-after-free reported by syzbot in hdm_disconnect(). See report and stack traces in the bug link below.
Reported-by: syzbot+916742d5d24f6c254761@syzkaller.appspotmail.com Cc: stable stable@kernel.org Closes: https://syzkaller.appspot.com/bug?extid=916742d5d24f6c254761 Fixes: 97a6f772f36b ("drivers: most: add USB adapter driver") Signed-off-by: Victoria Votokina Victoria.Votokina@kaspersky.com Link: https://patch.msgid.link/20251010105241.4087114-2-Victoria.Votokina@kaspersk... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/most/most_usb.c | 11 ++++------- 1 file changed, 4 insertions(+), 7 deletions(-)
--- a/drivers/most/most_usb.c +++ b/drivers/most/most_usb.c @@ -929,6 +929,10 @@ static void release_mdev(struct device * { struct most_dev *mdev = to_mdev_from_dev(dev);
+ kfree(mdev->busy_urbs); + kfree(mdev->cap); + kfree(mdev->conf); + kfree(mdev->ep_address); kfree(mdev); } /** @@ -1121,13 +1125,6 @@ static void hdm_disconnect(struct usb_in if (mdev->dci) device_unregister(&mdev->dci->dev); most_deregister_interface(&mdev->iface); - - kfree(mdev->busy_urbs); - kfree(mdev->cap); - kfree(mdev->conf); - kfree(mdev->ep_address); - put_device(&mdev->dci->dev); - put_device(&mdev->dev); }
static int hdm_suspend(struct usb_interface *interface, pm_message_t message)