From: Udipto Goswami quic_ugoswami@quicinc.com
[ Upstream commit 89e7252d6c7e7eeb31971cd7df987316ecc64ff5 ]
During enumeration or composition switch,a userspace process agnostic of the conventions of configs can try to create function symlinks even after the UDC is bound to current config which is not correct. Potentially it can create duplicates within the current config.
Prevent this by adding a check if udc_name already exists, then bail out of cfg_link.
Following is an example:
Step1: ln -s X1 ffs.a -->cfg_link --> usb_get_function(ffs.a) ->ffs_alloc
CFG->FUNC_LIST: <ffs.a> C->FUNCTION: <empty>
Step2: echo udc.name > /config/usb_gadget/g1/UDC --> UDC_store ->composite_bind ->usb_add_function
CFG->FUNC_LIST: <empty> C->FUNCTION: <ffs.a>
Step3: ln -s Y1 ffs.a -->cfg_link -->usb_get_function(ffs.a) ->ffs_alloc
CFG->FUNC_LIST: <ffs.a> C->FUNCTION: <ffs.a>
both the lists corresponds to the same function instance ffs.a but the usb_function* pointer is different because in step 3 ffs_alloc has created a new reference to usb_function* for ffs.a and added it to cfg_list.
Step4: Now a composition switch involving <ffs.b,ffs.a> is executed.
the composition switch will involve 3 things: 1. unlinking the previous functions existing 2. creating new symlinks 3. writing UDC
However, the composition switch is generally taken care by userspace process which creates the symlinks in its own nomenclature(X*) and removes only those. So it won't be able to remove Y1 which user had created by own.
Due to this the new symlinks cannot be created for ffs.a since the entry already exists in CFG->FUNC_LIST.
The state of the CFG->FUNC_LIST is as follows: CFG->FUNC_LIST: <ffs.a>
Fixes: 88af8bbe4ef7 ("usb: gadget: the start of the configfs interface") Signed-off-by: Krishna Kurapati PSSNV quic_kriskura@quicinc.com Signed-off-by: Udipto Goswami quic_ugoswami@quicinc.com Link: https://lore.kernel.org/r/20230201132308.31523-1-quic_ugoswami@quicinc.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/usb/gadget/configfs.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/drivers/usb/gadget/configfs.c b/drivers/usb/gadget/configfs.c index 891d8e4023221..5cbf4084daedc 100644 --- a/drivers/usb/gadget/configfs.c +++ b/drivers/usb/gadget/configfs.c @@ -428,6 +428,12 @@ static int config_usb_cfg_link( * from another gadget or a random directory. * Also a function instance can only be linked once. */ + + if (gi->composite.gadget_driver.udc_name) { + ret = -EINVAL; + goto out; + } + list_for_each_entry(iter, &gi->available_func, cfs_list) { if (iter != fi) continue;