linux-kernel - [PATCH 10/10] staging: lustre: fix error deref in ll_splice

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Date:   Tue, 01 May 2018 13:52:39 +1000
From:   NeilBrown <neilb@...e.com>
To:     Oleg Drokin <oleg.drokin@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        James Simmons <jsimmons@...radead.org>,
        Andreas Dilger <andreas.dilger@...el.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Lustre Development List <lustre-devel@...ts.lustre.org>
Subject: [PATCH 10/10] staging: lustre: fix error deref in ll_splice_alias().

d_splice_alias() can return an ERR_PTR().
If it does while debugging is enabled, the following
CDEBUG() will dereference that error and crash.

So add appropriate checking, and provide a separate
debug message for the error case.

Reported-by: James Simmons <jsimmons@...radead.org>
Fixes: e9d4f0b9f559 ("staging: lustre: llite: use d_splice_alias for directories.")
Signed-off-by: NeilBrown <neilb@...e.com>
---
 drivers/staging/lustre/lustre/llite/namei.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/lustre/lustre/llite/namei.c b/drivers/staging/lustre/lustre/llite/namei.c
index 6c9ec462eb41..24a6873d86a2 100644
--- a/drivers/staging/lustre/lustre/llite/namei.c
+++ b/drivers/staging/lustre/lustre/llite/namei.c
@@ -442,11 +442,15 @@ struct dentry *ll_splice_alias(struct inode *inode, struct dentry *de)
 	} else {
 		struct dentry *new = d_splice_alias(inode, de);
 
+		if (IS_ERR(new))
+			CDEBUG(D_DENTRY, "splice inode %p as %pd gives error %lu\n",
+			       inode, de, PTR_ERR(new));
 		if (new)
 			de = new;
 	}
-	CDEBUG(D_DENTRY, "Add dentry %p inode %p refc %d flags %#x\n",
-	       de, d_inode(de), d_count(de), de->d_flags);
+	if (!IS_ERR(de))
+		CDEBUG(D_DENTRY, "Add dentry %p inode %p refc %d flags %#x\n",
+		       de, d_inode(de), d_count(de), de->d_flags);
 	return de;
 }