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general protection fault in fuse_ctl_remove_conn

Message ID cedce932-4275-8d7e-fa4a-d7f44b8bfd85@I-love.SAKURA.ne.jp (mailing list archive)
State New, archived
Headers show

Commit Message

Tetsuo Handa April 28, 2018, 2:29 a.m. UTC 
From 9f41081f8bd6762a6f629e5e23e6d07a62bba69c Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date: Sat, 28 Apr 2018 11:24:09 +0900
Subject: [PATCH] fuse: don't keep inode-less dentry at fuse_ctl_add_dentry().

syzbot is reporting NULL pointer dereference at fuse_ctl_remove_conn() [1].
Since fc->ctl_ndents is incremented by fuse_ctl_add_conn() when new_inode()
failed, fuse_ctl_remove_conn() reaches an inode-less dentry and tries to
clear d_inode(dentry)->i_private field. Fix this by calling dput() rather
than incrementing fc->ctl_ndents when new_inode() failed.

[1] https://syzkaller.appspot.com/bug?id=f396d863067238959c91c0b7cfc10b163638cac6

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-by: syzbot <syzbot+32c236387d66c4516827@syzkaller.appspotmail.com>
Fixes: bafa96541b250a70 ("fuse: add control filesystem")
Cc: Miklos Szeredi <miklos@szeredi.hu>
---
 fs/fuse/control.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

Comments

Miklos Szeredi May 31, 2018, 2:27 p.m. UTC | #1 
On Sat, Apr 28, 2018 at 4:29 AM, Tetsuo Handa
<penguin-kernel@i-love.sakura.ne.jp> wrote:
> From 9f41081f8bd6762a6f629e5e23e6d07a62bba69c Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Date: Sat, 28 Apr 2018 11:24:09 +0900
> Subject: [PATCH] fuse: don't keep inode-less dentry at fuse_ctl_add_dentry().
>
> syzbot is reporting NULL pointer dereference at fuse_ctl_remove_conn() [1].
> Since fc->ctl_ndents is incremented by fuse_ctl_add_conn() when new_inode()
> failed, fuse_ctl_remove_conn() reaches an inode-less dentry and tries to
> clear d_inode(dentry)->i_private field. Fix this by calling dput() rather
> than incrementing fc->ctl_ndents when new_inode() failed.
>
> [1] https://syzkaller.appspot.com/bug?id=f396d863067238959c91c0b7cfc10b163638cac6

Slightly different fix pushed to:

  git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse.git for-next

Thanks,
Miklos
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Patch

diff --git a/fs/fuse/control.c b/fs/fuse/control.c
index b9ea99c..a651f8e 100644
--- a/fs/fuse/control.c
+++ b/fs/fuse/control.c
@@ -211,10 +211,12 @@  static struct dentry *fuse_ctl_add_dentry(struct dentry *parent,
 	if (!dentry)
 		return NULL;
 
-	fc->ctl_dentry[fc->ctl_ndents++] = dentry;
 	inode = new_inode(fuse_control_sb);
-	if (!inode)
+	if (!inode) {
+		dput(dentry);
 		return NULL;
+	}
+	fc->ctl_dentry[fc->ctl_ndents++] = dentry;
 
 	inode->i_ino = get_next_ino();
 	inode->i_mode = mode;