From: "Gustavo A. R. Silva" gustavo@embeddedor.com
[ Upstream commit 987f028b8637cfa7658aa456ae73f8f21a7a7f6f ]
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 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva gustavo@embeddedor.com Link: https://lore.kernel.org/r/20200120235326.GA29231@embeddedor.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/char/hpet.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/char/hpet.c b/drivers/char/hpet.c index 5b38d7a8202a1..38c2ae93ce492 100644 --- a/drivers/char/hpet.c +++ b/drivers/char/hpet.c @@ -112,7 +112,7 @@ struct hpets { unsigned long hp_delta; unsigned int hp_ntimer; unsigned int hp_which; - struct hpet_dev hp_dev[1]; + struct hpet_dev hp_dev[]; };
static struct hpets *hpets;