From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Wed, 14 Dec 2016 20:45:25 +0000 (-0800)
Subject: vfs,mm: fix return value of read() at s_maxbytes
X-Git-Tag: v4.14-rc1~1889
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=d05c5f7ba164aed3db02fb188c26d0dd94f5455b;p=platform%2Fkernel%2Flinux-rpi.git

vfs,mm: fix return value of read() at s_maxbytes

We truncated the possible read iterator to s_maxbytes in commit
c2a9737f45e2 ("vfs,mm: fix a dead loop in truncate_inode_pages_range()"),
but our end condition handling was wrong: it's not an error to try to
read at the end of the file.

Reading past the end should return EOF (0), not EINVAL.

See for example

  https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1649342
  http://lists.gnu.org/archive/html/bug-coreutils/2016-12/msg00008.html

where a md5sum of a maximally sized file fails because the final read is
exactly at s_maxbytes.

Fixes: c2a9737f45e2 ("vfs,mm: fix a dead loop in truncate_inode_pages_range()")
Reported-by: Joseph Salisbury <joseph.salisbury@canonical.com>
Cc: Wei Fang <fangwei1@huawei.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

diff --git a/mm/filemap.c b/mm/filemap.c
index 6956838..b06517b 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1637,7 +1637,7 @@ static ssize_t do_generic_file_read(struct file *filp, loff_t *ppos,
 	int error = 0;
 
 	if (unlikely(*ppos >= inode->i_sb->s_maxbytes))
-		return -EINVAL;
+		return 0;
 	iov_iter_truncate(iter, inode->i_sb->s_maxbytes);
 
 	index = *ppos >> PAGE_SHIFT;