linux-kernel - [PATCH 2/5] exec: binfmt_misc: shift filp_close(interp_file) from kill_node() to bm_evict

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Date:   Fri, 22 Sep 2017 16:36:44 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>
Cc:     Ben Woodard <woodard@...hat.com>,
        James Bottomley <James.Bottomley@...senPartnership.com>,
        Jim Foraker <foraker1@...l.gov>,
        Kees Cook <keescook@...omium.org>,
        Travis Gummels <tgummels@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 2/5] exec: binfmt_misc: shift filp_close(interp_file) from
 kill_node() to bm_evict_inode()

to ensure that load_misc_binary() can't use the partially destroyed
Node, see also the next patch.

The current logic looks wrong in any case, once we close interp_file
it doesn't make any sense to delay kfree(inode->i_private), this Node
is no longer valid. Even if the MISC_FMT_OPEN_FILE/interp_file checks
were not racy (they are), load_misc_binary() should not try to reopen
->interpreter if MISC_FMT_OPEN_FILE is set but ->interp_file is NULL.

And I can't understand why do we use filp_close(), not fput().

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 fs/binfmt_misc.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
index f4de5ae..040ed26 100644
--- a/fs/binfmt_misc.c
+++ b/fs/binfmt_misc.c
@@ -591,8 +591,13 @@ static struct inode *bm_get_inode(struct super_block *sb, int mode)
 
 static void bm_evict_inode(struct inode *inode)
 {
+	Node *e = inode->i_private;
+
+	if ((e->flags & MISC_FMT_OPEN_FILE) && e->interp_file)
+		filp_close(e->interp_file, NULL);
+
 	clear_inode(inode);
-	kfree(inode->i_private);
+	kfree(e);
 }
 
 static void kill_node(Node *e)
@@ -603,11 +608,6 @@ static void kill_node(Node *e)
 	list_del_init(&e->list);
 	write_unlock(&entries_lock);
 
-	if ((e->flags & MISC_FMT_OPEN_FILE) && e->interp_file) {
-		filp_close(e->interp_file, NULL);
-		e->interp_file = NULL;
-	}
-
 	dentry = e->dentry;
 	drop_nlink(d_inode(dentry));
 	d_drop(dentry);
-- 
2.5.0