[PATCH RFC] usb: gadget: uvc: configfs: prevent null-ptr-deref and double free

[syzbot]

From: gli...@google.com

If uvcg_config_create_children() fails in uvcg_attach_configfs(), the error
path calls config_group_put(&opts->func_inst.group). This drops the
reference count of the group to 0, triggering its release function,
uvc_func_item_release().

uvc_func_item_release() then calls
usb_put_function_instance(&opts->func_inst). However, at this point, the
usb_function_instance is not fully initialized. Specifically, fi->fd is
NULL because it is only assigned in try_get_usb_function_instance() after
alloc_inst() (which is uvc_alloc_inst()) returns successfully.
usb_put_function_instance() immediately dereferences fi->fd, resulting in a
null-pointer dereference.

Furthermore, if the null-pointer dereference didn't occur,
usb_put_function_instance() would proceed to call fi->free_func_inst(fi),
which maps to uvc_free_inst(). This function calls kfree(opts). After
config_group_put() returns, uvcg_attach_configfs() returns the error code
back to uvc_alloc_inst(), which then also calls kfree(opts), leading to a
double free.

Fix this by replacing config_group_put() with uvcg_config_remove_children()
in the error path of uvcg_attach_configfs(). This safely removes any
partially allocated configfs groups from the default_groups list and frees
them, without triggering the parent's release function. The parent opts
structure will then be safely and correctly freed by the existing
kfree(opts) in uvc_alloc_inst().

Oops: general protection fault, probably for non-canonical address
0xdffffc0000000001: 0000 [#1] SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
CPU: 0 UID: 0 PID: 5875 Comm: syz-executor234 Not tainted
RIP: 0010:usb_put_function_instance+0x54/0xb0
drivers/usb/gadget/functions.c:76
Call Trace:
<TASK>
config_item_cleanup fs/configfs/item.c:128 [inline]
config_item_release+0x13a/0x2d0 fs/configfs/item.c:137
config_group_put include/linux/configfs.h:102 [inline]
uvcg_attach_configfs+0x56/0x60
drivers/usb/gadget/function/uvc_configfs.c:3832
uvc_alloc_inst+0x6f9/0xa90 drivers/usb/gadget/function/f_uvc.c:999
try_get_usb_function_instance drivers/usb/gadget/functions.c:28 [inline]
usb_get_function_instance+0xe3/0x2f0 drivers/usb/gadget/functions.c:44
function_make+0x127/0x360 drivers/usb/gadget/configfs.c:626
configfs_mkdir+0x4f6/0x9e0 fs/configfs/dir.c:1360

Fixes: efbf0af70b4f ("usb: gadget: uvc: configfs: Allocate groups dynamically")
Assisted-by: Gemini:gemini-3.1-pro-preview syzbot
Link: https://syzkaller.appspot.com/ai_job?id=48ba7a22-ac64-47f1-9ab8-a7f7b0f6e195
Signed-off-by: gli...@google.com
To: <gli...@google.com>
To: "Greg Kroah-Hartman" <gre...@linuxfoundation.org>
To: <linu...@vger.kernel.org>
To: "Laurent Pinchart" <laurent....@ideasonboard.com>
Cc: "Andrew Morton" <ak...@linux-foundation.org>
Cc: "Andy Shevchenko" <andriy.s...@intel.com>
Cc: "Christophe JAILLET" <christoph...@wanadoo.fr>
Cc: "Kees Cook" <ke...@kernel.org>
Cc: <linux-...@vger.kernel.org>
Cc: "Akash Kumar" <quic_...@quicinc.com>
Cc: "Randy Dunlap" <rdu...@infradead.org>

---
diff --git a/drivers/usb/gadget/function/uvc_configfs.c b/drivers/usb/gadget/function/uvc_configfs.c
index 70a1415ea..da0fc8084 100644
--- a/drivers/usb/gadget/function/uvc_configfs.c
+++ b/drivers/usb/gadget/function/uvc_configfs.c
@@ -3829,7 +3829,7 @@ int uvcg_attach_configfs(struct f_uvc_opts *opts)
ret = uvcg_config_create_children(&opts->func_inst.group,
&uvc_func_type);
if (ret < 0)
- config_group_put(&opts->func_inst.group);
+ uvcg_config_remove_children(&opts->func_inst.group);

return ret;
}


base-commit: a13c140cc289c0b7b3770bce5b3ad42ab35074aa
--
This is an AI-generated patch subject to moderation.
Reply with '#syz upstream' to Sign-off the patch as a human author
and send it to the upstream kernel mailing lists.
Reply with '#syz reject' to reject it ('#syz unreject' to undo).

See https://goo.gle/syzbot-ai-patches for information about AI-generated patches.
You can comment on the patch as usual, syzbot will try to address
the comments and send a new version of the patch if necessary.
syzbot engineers can be reached at syzk...@googlegroups.com.