Re: [PATCH v4 1/5] fuse: Fix leak in fuse_dentry_automount() error path

On Fri, 21 May 2021 09:54:19 +0200
Miklos Szeredi [off-list ref] wrote:

On Thu, 20 May 2021 at 21:45, Al Viro [off-list ref] wrote:

quoted

On Thu, May 20, 2021 at 05:46:50PM +0200, Greg Kurz wrote:

quoted

Some rollback was forgotten during the addition of crossmounts.

Have you actually tested that?  Because I strongly suspect that
by that point the ownership of fc and fm is with sb and those
should be taken care of by deactivate_locked_super().

Not quite.  Patch looks correct because destruction of fm is done in
fuse_put_super(), which only gets called if the sb initialization gets
as far as setting up sb->s_root, which only happens after the
successful fuse_fill_super_submount() call in this case.

Doing the destruction from the various ->kill_sb() instances instead
of from ->put_super() would also fix this, but I'm not quite sure that
that would be any cleaner.

As saying in the answer I've just posted, a failure in
fuse_fill_super_submount() causes an actual crash because
fuse_mount_remove() logically assumes fm to already be in
fc->mounts, which isn't the case at this point.

In the root mount case, this is handled by taking back
the ownership on fm, i.e. do the rollback *and* clear
sb->s_fs_info. It seems that the same should be done
for submounts.

Thanks,
Miklos

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