[PATCH] fix offset checks in do_sendfile to use unsigned values (try #2)

[Jeff Layton]

This is the second version of this patch. Some of the checks do need
to use signed values. This patch should be more correct in that regard.
This also adds a check to make sure that "pos + count" doesn't
overflow.

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 against "max".

Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
---
 fs/read_write.c |   21 ++++++++++++---------
 1 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/fs/read_write.c b/fs/read_write.c
index 6c8c55d..2c5b402 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, newpos;
 	ssize_t retval;
 	int fput_needed_in, fput_needed_out, fl;
 
@@ -835,14 +835,16 @@ static ssize_t do_sendfile(int out_fd, int in_fd, loff_t *ppos,
 		goto fput_out;
 	count = retval;
 
-	if (!max)
-		max = min(in_inode->i_sb->s_maxbytes, out_inode->i_sb->s_maxbytes);
-
-	pos = *ppos;
 	retval = -EINVAL;
-	if (unlikely(pos < 0))
+	if (unlikely(*ppos < 0))
 		goto fput_out;
-	if (unlikely(pos + count > max)) {
+
+	if (!max)
+		max = min(in_inode->i_sb->s_maxbytes,
+			  out_inode->i_sb->s_maxbytes);
+	pos = (unsigned long long) *ppos;
+	newpos = pos + count;
+	if (unlikely(newpos > max || newpos < count)) {
 		retval = -EOVERFLOW;
 		if (pos >= max)
 			goto fput_out;
@@ -869,7 +871,8 @@ static ssize_t do_sendfile(int out_fd, int in_fd, loff_t *ppos,
 
 	inc_syscr(current);
 	inc_syscw(current);
-	if (*ppos > max)
+	pos = (unsigned long long) *ppos;
+	if (pos > max)
 		retval = -EOVERFLOW;
 
 fput_out:
-- 
1.6.2.5


--=-F43uCi3SlHVZxYj2YkbQ--

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