[LTP] [PATCH v2] syscalls/statmount07: change "invalid buffer size" test

[Cyril Hrubis]

Hi!
> Signed-off-by: Jan Stancek <jstancek@redhat.com>
> ---
>  testcases/kernel/syscalls/statmount/statmount07.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/testcases/kernel/syscalls/statmount/statmount07.c b/testcases/kernel/syscalls/statmount/statmount07.c
> index 0cc83429872f..58fcc20acce7 100644
> --- a/testcases/kernel/syscalls/statmount/statmount07.c
> +++ b/testcases/kernel/syscalls/statmount/statmount07.c
> @@ -20,10 +20,10 @@
>  static struct statmount *st_mount;
>  static struct statmount *st_mount_null;
>  static struct statmount *st_mount_small;
> +static struct statmount *st_mount_bad;
>  static uint64_t mnt_id;
>  static uint64_t mnt_id_dont_exist = -1;
>  static size_t buff_size;
> -static size_t buff_size_invalid = -1;
>  
>  struct tcase {
>  	int exp_errno;
> @@ -90,12 +90,12 @@ struct tcase {
>  	},
>  	{
>  		EFAULT,
> -		"invalid buffer size",
> +		"buffer crosses to PROT_NONE",
>  		&mnt_id,
>  		0,
>  		0,
> -		&buff_size_invalid,
> -		&st_mount
> +		&buff_size,
> +		&st_mount_bad
>  	},
>  	{
>  		EFAULT,
> @@ -139,6 +139,7 @@ static struct tst_test test = {
>  	.bufs = (struct tst_buffers []) {
>  		{&st_mount, .size = sizeof(struct statmount)},
>  		{&st_mount_small, .size = sizeof(struct statmount)},
> +		{&st_mount_bad, .size = 1},

With this we create a mapping where PROT_NONE is before the buffer, not
after it, since guarded buffers are primarily guarding about off-by-one
at the start of the buffer. There is a canaray after after the allocated
buffer that will potentialy be rewritten, but that would be detected
only at the test exit.

If I remmeber correctly the mappings will look like:

| PROT_NONE |_ CANARY BYTES |
             ^
	     And this is our 1-byte buffer.

-- 
Cyril Hrubis
chrubis@suse.cz