linux-kernel - Re: [PATCH linux] ext4: Delete useless ret assignment

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Date:   Thu, 6 Jan 2022 16:59:46 -0800
From:   harshad shirwadkar <harshadshirwadkar@...il.com>
To:     Lukas Czerner <lczerner@...hat.com>
Cc:     "Theodore Ts'o" <tytso@....edu>, cgel.zte@...il.com,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Ext4 Developers List <linux-ext4@...r.kernel.org>,
        linux-kernel@...r.kernel.org, luo penghao <luo.penghao@....com.cn>,
        Zeal Robot <zealci@....com.cn>
Subject: Re: [PATCH linux] ext4: Delete useless ret assignment

First of all thanks for catching this. Yeah, I think the right thing
to do here is to return the return value up to the caller. Also, I
agree with Lukas, we should only set fc_modified_inodes_size if the
allocation succeeds. Luo, would you be okay updating the patch to
include these changes?

Thanks,
Harshad

On Thu, Jan 6, 2022 at 2:58 AM Lukas Czerner <lczerner@...hat.com> wrote:
>
> On Wed, Jan 05, 2022 at 11:44:39PM -0500, Theodore Ts'o wrote:
> > On Thu, Dec 30, 2021 at 06:29:05AM +0000, cgel.zte@...il.com wrote:
> > > From: luo penghao <luo.penghao@....com.cn>
> > >
> > > The assignments in these two places will be overwritten by new
> > > assignments later, so they should be deleted.
> > >
> > > The clang_analyzer complains as follows:
> > >
> > > fs/ext4/fast_commit.c
> > >
> > > Value stored to 'ret' is never read
> >
> > I suspect the right answer here is that we *should* be checking the
> > return value, and reflecting the error up to caller, if appropriate.
> >
> > Harshad, what do you think?
>
> Indeed we absolutely *must* be checking the return value and bail out
> otherwise we risk overwriting kernel memory among other possible
> problems.
>
> See ext4_fc_record_modified_inode() where we increment
> fc_modified_inodes_size before the actual reallocation which in case of
> allocation failure will leave us with elevated fc_modified_inodes_size
> and the next call to ext4_fc_record_modified_inode() can modify
> fc_modified_inodes[] out of bounds.
>
> In addition to checking the return value we should probably also move
> incrementing the fc_modified_inodes_size until after the successful
> reallocation in order to avoid such pitfalls.
>
> Thanks!
> -Lukas
>
> >
> >                                       - Ted
> >
> > >
> > > Reported-by: Zeal Robot <zealci@....com.cn>
> > > Signed-off-by: luo penghao <luo.penghao@....com.cn>
> > > ---
> > >  fs/ext4/fast_commit.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c
> > > index 8ea5a81..8d5d044 100644
> > > --- a/fs/ext4/fast_commit.c
> > > +++ b/fs/ext4/fast_commit.c
> > > @@ -1660,7 +1660,7 @@ static int ext4_fc_replay_add_range(struct super_block *sb,
> > >             return 0;
> > >     }
> > >
> > > -   ret = ext4_fc_record_modified_inode(sb, inode->i_ino);
> > > +   ext4_fc_record_modified_inode(sb, inode->i_ino);
> > >
> > >     start = le32_to_cpu(ex->ee_block);
> > >     start_pblk = ext4_ext_pblock(ex);
> > > @@ -1785,7 +1785,7 @@ ext4_fc_replay_del_range(struct super_block *sb, struct ext4_fc_tl *tl,
> > >             return 0;
> > >     }
> > >
> > > -   ret = ext4_fc_record_modified_inode(sb, inode->i_ino);
> > > +   ext4_fc_record_modified_inode(sb, inode->i_ino);
> > >
> > >     jbd_debug(1, "DEL_RANGE, inode %ld, lblk %d, len %d\n",
> > >                     inode->i_ino, le32_to_cpu(lrange.fc_lblk),
> > > --
> > > 2.15.2
> > >
> > >
> >
>