USB: Replace zero-length array with flexible-array member

The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Link: https://lore.kernel.org/r/20200220132017.GA29262@embeddedor
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

4 files changed, 4 insertions, 4 deletions

diff --git a/include/linux/usb/audio-v2.h b/include/linux/usb/audio-v2.h
index ba4b3e3327ff..5e31740c7e40 100644
--- a/include/linux/usb/audio-v2.h
+++ b/include/linux/usb/audio-v2.h
@@ -153,7 +153,7 @@ struct uac2_feature_unit_descriptor {
 	__u8 bSourceID;
 	/* bmaControls is actually u32,
 	 * but u8 is needed for the hybrid parser */
-	__u8 bmaControls[0]; /* variable length */
+	__u8 bmaControls[]; /* variable length */
 } __attribute__((packed));
 
 /* 4.9.2 Class-Specific AS Interface Descriptor */
diff --git a/include/linux/usb/audio-v3.h b/include/linux/usb/audio-v3.h
index 6b708434b7f9..c69a6f2e6837 100644
--- a/include/linux/usb/audio-v3.h
+++ b/include/linux/usb/audio-v3.h
@@ -109,7 +109,7 @@ struct uac3_feature_unit_descriptor {
 	__u8 bSourceID;
 	/* bmaControls is actually u32,
 	 * but u8 is needed for the hybrid parser */
-	__u8 bmaControls[0]; /* variable length */
+	__u8 bmaControls[]; /* variable length */
 	/* wFeatureDescrStr omitted */
 } __attribute__((packed));
 
diff --git a/include/linux/usb/gadget.h b/include/linux/usb/gadget.h
index 124462d65eac..9411c08a5c7e 100644
--- a/include/linux/usb/gadget.h
+++ b/include/linux/usb/gadget.h
@@ -767,7 +767,7 @@ struct usb_gadget_strings {
 
 struct usb_gadget_string_container {
 	struct list_head        list;
-	u8                      *stash[0];
+	u8                      *stash[];
 };
 
 /* put descriptor for string with that id into buf (buflen >= 256) */
diff --git a/include/linux/usb/hcd.h b/include/linux/usb/hcd.h
index 712b2a603645..e12105ed3834 100644
--- a/include/linux/usb/hcd.h
+++ b/include/linux/usb/hcd.h
@@ -228,7 +228,7 @@ struct usb_hcd {
 	/* The HC driver's private data is stored at the end of
 	 * this structure.
 	 */
-	unsigned long hcd_priv[0]
+	unsigned long hcd_priv[]
 			__attribute__ ((aligned(sizeof(s64))));
 };