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fuse: fix control dir setup and teardown 

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 by only adding the dentry to the array after being fully set up.

When tearing down the control directory, do d_invalidate() on it to get rid
of any mounts that might have been added.

[1] https://syzkaller.appspot.com/bug?id=f396d863067238959c91c0b7cfc10b163638cac6
Reported-by: syzbot <syzbot+32c236387d66c4516827@syzkaller.appspotmail.com>
Fixes: bafa96541b ("[PATCH] fuse: add control filesystem")
Cc: <stable@vger.kernel.org> # v2.6.18
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Miklos Szeredi 2018-05-31 12:26:10 +02:00
parent 8a301eb16d
commit 6becdb601b
1 changed files with 10 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

13
fs/fuse/control.c
View File

@ -211,10 +211,11 @@ 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;
}
inode->i_ino = get_next_ino();
inode->i_mode = mode;
@ -228,6 +229,9 @@ static struct dentry *fuse_ctl_add_dentry(struct dentry *parent,
set_nlink(inode, nlink);
inode->i_private = fc;
d_add(dentry, inode);
fc->ctl_dentry[fc->ctl_ndents++] = dentry;
return dentry;
}
@ -284,7 +288,10 @@ void fuse_ctl_remove_conn(struct fuse_conn *fc)
for (i = fc->ctl_ndents - 1; i >= 0; i--) {
struct dentry *dentry = fc->ctl_dentry[i];
d_inode(dentry)->i_private = NULL;
d_drop(dentry);
if (!i) {
/* Get rid of submounts: */
d_invalidate(dentry);
}
dput(dentry);
}
drop_nlink(d_inode(fuse_control_sb->s_root));