linux-kernel - [PATCH v2] Make __xfs_xattr_put_listen preperly report errors.

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Message-Id: <1472458353-19615-1-git-send-email-asavkov@redhat.com>
Date:   Mon, 29 Aug 2016 10:12:33 +0200
From:   Artem Savkov <asavkov@...hat.com>
To:     Dave Chinner <david@...morbit.com>
Cc:     Eric Sandeen <sandeen@...deen.net>, xfs@....sgi.com,
        linux-kernel@...r.kernel.org, Artem Savkov <asavkov@...hat.com>
Subject: [PATCH v2] Make __xfs_xattr_put_listen preperly report errors.

Commit 2a6fba6 "xfs: only return -errno or success from attr ->put_listent"
changes the returnvalue of __xfs_xattr_put_listen to 0 in case when there is
insufficient space in the buffer assuming that setting context->count to -1
would be enough, but all of the ->put_listent callers only check seen_enough.
This results in a failed assertion:
XFS: Assertion failed: context->count >= 0, file: fs/xfs/xfs_xattr.c, line: 175
in insufficient buffer size case.

This is only reproducible with at least 2 xattrs and only when the buffer
gets depleted before the last one.

Furthermore if buffersize is such that it is enough to hold the last xattr's
name, but not enough to hold the sum of preceeding xattr names listxattr won't
fail with ERANGE, but will suceed returning last xattr's name without the
first character. The first character end's up overwriting data stored at
(context->alist - 1).

Signed-off-by: Artem Savkov <asavkov@...hat.com>
---
 fs/xfs/xfs_xattr.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/xfs/xfs_xattr.c b/fs/xfs/xfs_xattr.c
index ea62245..6290093 100644
--- a/fs/xfs/xfs_xattr.c
+++ b/fs/xfs/xfs_xattr.c
@@ -147,6 +147,7 @@ __xfs_xattr_put_listent(
 	arraytop = context->count + prefix_len + namelen + 1;
 	if (arraytop > context->firstu) {
 		context->count = -1;	/* insufficient space */
+		context->seen_enough = 1;
 		return 0;
 	}
 	offset = (char *)context->alist + context->count;
-- 
2.7.4