[PATCH] fix offset checks in do_sendfile to use unsigned values

[Jeff Layton <jlayton@redhat.com>]

If do_sendfile is called with a "max" value of 0, it grabs the lesser
s_maxbytes value of the two superblocks to use instead. There's a
problem here however. s_maxbytes is an unsigned long long and it gets
cast to a signed value. If both s_maxbytes values are large enough, max
will end up being negative and the comparisons in this code won't work
correctly.

Change do_sendfile to use unsigned values internally for the offset
checks.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 fs/read_write.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/read_write.c b/fs/read_write.c
index 6c8c55d..36899ff 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -788,11 +788,11 @@ SYSCALL_DEFINE5(pwritev, unsigned long, fd, const struct iovec __user *, vec,
 }
 
 static ssize_t do_sendfile(int out_fd, int in_fd, loff_t *ppos,
-			   size_t count, loff_t max)
+			   size_t count, unsigned long long max)
 {
 	struct file * in_file, * out_file;
 	struct inode * in_inode, * out_inode;
-	loff_t pos;
+	unsigned long long pos;
 	ssize_t retval;
 	int fput_needed_in, fput_needed_out, fl;
 
@@ -838,7 +838,7 @@ static ssize_t do_sendfile(int out_fd, int in_fd, loff_t *ppos,
 	if (!max)
 		max = min(in_inode->i_sb->s_maxbytes, out_inode->i_sb->s_maxbytes);
 
-	pos = *ppos;
+	pos = (unsigned long long) *ppos;
 	retval = -EINVAL;
 	if (unlikely(pos < 0))
 		goto fput_out;
-- 
1.6.0.6