Re: [PATCH] usb: gadget: f_midi: Annotate struct f_midi with __counted_by

[Gustavo A. R. Silva]

On 9/15/23 13:59, Kees Cook wrote:

Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
(for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).

As found with Coccinelle[1], add __counted_by for struct f_midi.
Additionally, since the element count member must be set before accessing
the annotated flexible array member, move its initialization earlier.

[1] 
https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci

Cc: Greg Kroah-Hartman 
Cc: John Keeping 
Cc: Peter Chen 
Cc: Hulk Robot 
Cc: Allen Pais 
Cc: Will McVicker 
Cc: Davidlohr Bueso 
Cc: Zhang Qilong 
Cc: linux-...@vger.kernel.org
Signed-off-by: Kees Cook 


Reviewed-by: Gustavo A. R. Silva 

Thanks
--
Gustavo


---
  drivers/usb/gadget/function/f_midi.c | 4 ++--
  1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/gadget/function/f_midi.c 
b/drivers/usb/gadget/function/f_midi.c
index 2d02f25f9597..033e347554db 100644
--- a/drivers/usb/gadget/function/f_midi.c
+++ b/drivers/usb/gadget/function/f_midi.c
@@ -99,7 +99,7 @@ struct f_midi {
unsigned int in_last_port;
unsigned char free_ref;
  
-	struct gmidi_in_port	in_ports_array[/* in_ports */];

+   struct gmidi_in_portin_ports_array[] __counted_by(in_ports);
  };
  
  static inline struct f_midi *func_to_midi(struct usb_function *f)

@@ -1349,6 +1349,7 @@ static struct usb_function *f_midi_alloc(struct 
usb_function_instance *fi)
status = -ENOMEM;
goto setup_fail;
}
+   midi->in_ports = opts->in_ports;
  
  	for (i = 0; i < opts->in_ports; i++)

midi->in_ports_array[i].cable = i;
@@ -1359,7 +1360,6 @@ static struct usb_function *f_midi_alloc(struct 
usb_function_instance *fi)
status = -ENOMEM;
goto midi_free;
}
-   midi->in_ports = opts->in_ports;
midi->out_ports = opts->out_ports;
midi->index = opts->index;
midi->buflen = opts->buflen;

[PATCH] usb: gadget: f_midi: Annotate struct f_midi with __counted_by

[Kees Cook]

Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
(for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).

As found with Coccinelle[1], add __counted_by for struct f_midi.
Additionally, since the element count member must be set before accessing
the annotated flexible array member, move its initialization earlier.

[1] 
https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci

Cc: Greg Kroah-Hartman 
Cc: John Keeping 
Cc: Peter Chen 
Cc: Hulk Robot 
Cc: Allen Pais 
Cc: Will McVicker 
Cc: Davidlohr Bueso 
Cc: Zhang Qilong 
Cc: linux-...@vger.kernel.org
Signed-off-by: Kees Cook 
---
 drivers/usb/gadget/function/f_midi.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/gadget/function/f_midi.c 
b/drivers/usb/gadget/function/f_midi.c
index 2d02f25f9597..033e347554db 100644
--- a/drivers/usb/gadget/function/f_midi.c
+++ b/drivers/usb/gadget/function/f_midi.c
@@ -99,7 +99,7 @@ struct f_midi {
unsigned int in_last_port;
unsigned char free_ref;
 
-   struct gmidi_in_portin_ports_array[/* in_ports */];
+   struct gmidi_in_portin_ports_array[] __counted_by(in_ports);
 };
 
 static inline struct f_midi *func_to_midi(struct usb_function *f)
@@ -1349,6 +1349,7 @@ static struct usb_function *f_midi_alloc(struct 
usb_function_instance *fi)
status = -ENOMEM;
goto setup_fail;
}
+   midi->in_ports = opts->in_ports;
 
for (i = 0; i < opts->in_ports; i++)
midi->in_ports_array[i].cable = i;
@@ -1359,7 +1360,6 @@ static struct usb_function *f_midi_alloc(struct 
usb_function_instance *fi)
status = -ENOMEM;
goto midi_free;
}
-   midi->in_ports = opts->in_ports;
midi->out_ports = opts->out_ports;
midi->index = opts->index;
midi->buflen = opts->buflen;
-- 
2.34.1