linux-kernel - [PATCH] fs: fix possible extra iput() in do

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Date:   Thu, 28 Sep 2023 14:11:29 +0100
From:   Luís Henriques <lhenriques@...e.de>
To:     Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        David Howells <dhowells@...hat.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Luís Henriques <lhenriques@...e.de>
Subject: [PATCH] fs: fix possible extra iput() in do_unlinkat()

Because inode is being initialised before checking if dentry is negative,
and the ihold() is only done if the dentry is *not* negative, the cleanup
code may end-up doing an extra iput() on that inode.

Fixes: b18825a7c8e3 ("VFS: Put a small type field into struct dentry::d_flags")
Signed-off-by: Luís Henriques <lhenriques@...e.de>
---
Hi!

I was going to also remove the 'if (inode)' before the 'iput(inode)',
because 'iput()' already checks for NULL anyway.  But since I probably
wouldn't have caught this bug if it wasn't for that 'if', I decided to
keep it there.  But I can send v2 with that change too if you prefer.

Cheers,
--
Luís

 fs/namei.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 567ee547492b..156a570d7831 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4386,11 +4386,9 @@ int do_unlinkat(int dfd, struct filename *name)
 	if (!IS_ERR(dentry)) {
 
 		/* Why not before? Because we want correct error value */
-		if (last.name[last.len])
+		if (last.name[last.len] || d_is_negative(dentry))
 			goto slashes;
 		inode = dentry->d_inode;
-		if (d_is_negative(dentry))
-			goto slashes;
 		ihold(inode);
 		error = security_path_unlink(&path, dentry);
 		if (error)