eventfd: strictly check the count parameter of eventfd_write to avoid inputting illegal strings

Since eventfd's document has clearly stated: A write(2) call adds
the 8-byte integer value supplied in its buffer to the counter.

However, in the current implementation, the following code snippet
did not cause an error:

	char str[16] = "hello world";
	uint64_t value;
	ssize_t size;
	int fd;

	fd = eventfd(0, 0);
	size = write(fd, &str, strlen(str));
	printf("eventfd: test writing a string, size=%ld\n", size);
	size = read(fd, &value, sizeof(value));
	printf("eventfd: test reading as uint64, size=%ld, valus=0x%lX\n",
	       size, value);

	close(fd);

And its output is:
eventfd: test writing a string, size=8
eventfd: test reading as uint64, size=8, valus=0x6F77206F6C6C6568

By checking whether count is equal to sizeof(ucnt), such errors
could be detected. It also follows the requirements of the manual.

Signed-off-by: Wen Yang <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Cc: Alexander Viro <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: David Woodhouse <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Eric Biggers <[email protected]>
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Christian Brauner <[email protected]>

0 files changed, 0 insertions, 0 deletions