Skip to content

Commit

Permalink
USB: serial: garmin_gps: Use flexible-array member
Browse files Browse the repository at this point in the history
Old code in the kernel uses 1-byte and 0-byte arrays to indicate the
presence of a "variable length array":

struct something {
    int length;
    u8 data[1];
};

struct something *instance;

instance = kmalloc(sizeof(*instance) + size, GFP_KERNEL);
instance->length = size;
memcpy(instance->data, source, size);

There is also 0-byte arrays. Both cases pose confusion for things like
sizeof(), CONFIG_FORTIFY_SOURCE, etc.[1] Instead, the preferred mechanism
to declare variable-length types such as the one above is a flexible array
member[2] which need to be the last member of a structure and empty-sized:

struct something {
        int stuff;
        u8 data[];
};

Also, 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
unadvertenly introduced[3] to the codebase from now on.

[1] https://github.com/KSPP/linux/issues/21
[2] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[3] commit 7649773 ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
  • Loading branch information
Gustavo A. R. Silva authored and Johan Hovold committed Jan 17, 2020
1 parent e642158 commit 50c3c5e
Showing 1 changed file with 1 addition and 1 deletion.
2 changes: 1 addition & 1 deletion drivers/usb/serial/garmin_gps.c
Original file line number Diff line number Diff line change
@@ -104,7 +104,7 @@ struct garmin_packet {
int seq;
/* the real size of the data array, always > 0 */
int size;
__u8 data[1];
__u8 data[];
};

/* structure used to keep the current state of the driver */

0 comments on commit 50c3c5e

Please sign in to comment.