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i_private), this Node is no
longer valid.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().

Link: http://lkml.kernel.org/r/20170922143644.GA17216@redhat.com
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Ben Woodard <woodard@redhat.com>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Jim Foraker <foraker1@llnl.gov>
Cc: <tdhooge@llnl.gov>
Cc: Travis Gummels <tgummels@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
index 6451e7520e053fd53ddf1a0ef947575e1042234e..203598ccb40adecf5b70f6ade2f31be06054a6a6 100644 (file)
--- a/fs/binfmt_misc.c
+++ b/fs/binfmt_misc.c
@@ -594,8 +594,13 @@ 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)
@@ -606,11 +611,6 @@ 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);