LinuxKPI: Fix simple_read_from_buffer for zero-size and off-the-end reads

I noticed that the buf_size < 0 check can never be true (it's a
size_t) and decided to check for this condition by an alternate
expression, and I also noticed that a read_size of 0 would incorrectly
return -EFAULT.  Instead, return success for both of these cases as
reading beyond the EOF of a normal file also returns EOF, not EINVAL.

Reviewed by:	bz
Sponsored by:	AFRL, DARPA
Differential Revision:	https://reviews.freebsd.org/D55845

1 files changed, 2 insertions, 2 deletions

diff --git a/sys/compat/linuxkpi/common/include/linux/fs.h b/sys/compat/linuxkpi/common/include/linux/fs.h
index 40e1b396fe86..7e28be070850 100644
--- a/sys/compat/linuxkpi/common/include/linux/fs.h
+++ b/sys/compat/linuxkpi/common/include/linux/fs.h
@@ -368,8 +368,8 @@ simple_read_from_buffer(void __user *dest, size_t read_size, loff_t *ppos,
 	size_t buf_remain = buf_size - *ppos;
 	ssize_t num_read;
 
-	if (buf_remain < 0 || buf_remain > buf_size)
-		return -EINVAL;
+	if (*ppos >= buf_size || read_size == 0)
+		return (0);
 
 	if (read_size > buf_remain)
 		read_size = buf_remain;