linux-kernel - Re: Patch for a overwriting/corruption of the file system

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Date:   Tue, 14 Mar 2023 18:13:27 +0100
From:   Christian Brauner <brauner@...nel.org>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Kirtikumar Anandrao Ramchandani <kirtiar15502@...il.com>,
        security@...nel.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        Linus Torvalds <torvalds@...uxfoundation.org>
Subject: Re: Patch for a overwriting/corruption of the file system

On Tue, Mar 14, 2023 at 04:57:08PM +0000, Al Viro wrote:
> On Tue, Mar 14, 2023 at 10:55:39AM +0100, Christian Brauner wrote:
> > On Mon, Mar 13, 2023 at 11:32:08AM +0100, Greg KH wrote:
> > > On Mon, Mar 13, 2023 at 03:54:55PM +0530, Kirtikumar Anandrao Ramchandani wrote:
> > > > Seems like again it got rejected. I am sending it in the body if it works:
> > > > 
> > > > >From 839cae91705e044b49397590f2d85a5dd289f0c5 Mon Sep 17 00:00:00 2001
> > > > From: KirtiRamchandani <kirtar15502@...il.com>
> > > > Date: Mon, 13 Mar 2023 15:05:08 +0530
> > > > Subject: [PATCH] Fix bug in affs_rename() function. The `affs_rename()`
> > > >  function in the AFFS filesystem has a bug that can cause the `retval`
> > > >  variable to be overwritten before it is used. Specifically, the function
> > > >  assigns `retval` a value in two separate code blocks, but then only checks
> > > >  its value in one of those blocks. This commit fixes the bug by ensuring
> > > > that
> > > >  `retval` is properly checked in both code blocks.
> > > > 
> > > > Signed-off-by: KirtiRamchandani <kirtar15502@...il.com>
> > > > ---
> > > >  namei.c | 4++++--
> > > >  1 file changed, 4 insertions(+), 2 deletion(-)
> > > > 
> > > > diff --git a/fs/affs/namei.c b/fs/affs/namei.c
> > > > index d1084e5..a54c700 100644
> > > > --- a/fs/affs/namei.c
> > > > +++ b/fs/affs/namei.c
> > > > @@ -488,7 +488,8 @@ affs_xrename(struct inode *old_dir, struct dentry
> > > > *old_dentry,
> > > >         affs_lock_dir(new_dir);
> > > >         retval = affs_insert_hash(new_dir, bh_old);
> > > >         affs_unlock_dir(new_dir);
> > > > -
> > > > +       if (retval)
> > > > +               goto done;
> > > 
> > > The patch is corrupted and can not be applied.
> > 
> > Yeah, that patch is pretty borked. This should probably be sm like:
> > 
> > >From f3a7758bb53cc776820656c6ac66b13fb8ed9022 Mon Sep 17 00:00:00 2001
> > From: KirtiRamchandani <kirtar15502@...il.com>
> > Date: Tue, 14 Mar 2023 10:49:38 +0100
> > Subject: [PATCH] affs: handle errors in affs_xrename()
> > 
> > Fix a bug in the affs_xrename() function. The affs_xrename() function in
> > the AFFS filesystem has a bug that can cause the retval variable to be
> > overwritten before it is used. Specifically, the function assigns retval
> > a value in two separate code blocks, but then only checks its value in
> > one of those blocks. This commit fixes the bug by ensuring that retval
> > is properly checked in both code blocks.
> 
> "Properly checked" as in...?
> 
> > Signed-off-by: KirtiRamchandani <kirtar15502@...il.com>
> > ---
> >  fs/affs/namei.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/fs/affs/namei.c b/fs/affs/namei.c
> > index d12ccfd2a83d..98525d69391d 100644
> > --- a/fs/affs/namei.c
> > +++ b/fs/affs/namei.c
> > @@ -488,6 +488,8 @@ affs_xrename(struct inode *old_dir, struct dentry *old_dentry,
> >  	affs_lock_dir(new_dir);
> >  	retval = affs_insert_hash(new_dir, bh_old);
> >  	affs_unlock_dir(new_dir);
> > +	if (retval)
> > +		goto done;
> 
> OK, so you've got an IO error and insertion has failed.  Both entries had already
> been removed from their directories.  Sure, we must report an error, but why is
> leaking *both* entries the right thing to do?
> 
> >  	/* Insert new into the old directory with the old name. */
> >  	affs_copy_name(AFFS_TAIL(sb, bh_new)->name, old_dentry);
> > @@ -495,6 +497,8 @@ affs_xrename(struct inode *old_dir, struct dentry *old_dentry,
> >  	affs_lock_dir(old_dir);
> >  	retval = affs_insert_hash(old_dir, bh_new);
> >  	affs_unlock_dir(old_dir);
> > +	if (retval)
> > +		goto done;
> >  done:
> 
> Really?  How could that possibly make any sense?  I mean, look for the target of
> that goto...
> 
> The bug here (AFFS awful layout aside) is that error from the first insert_hash
> is always lost.  And it needs to be reported.  But this is no way to fix that.

Note that I formatted that thing into something we can look at on the
list from the borked attachment; not acked it...