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

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Date:   Wed, 12 Jan 2022 21:48:52 +0530
From:   riteshh <riteshh@...ux.ibm.com>
To:     harshad shirwadkar <harshadshirwadkar@...il.com>,
        luo penghao <luo.penghao@....com.cn>
Cc:     Lukas Czerner <lczerner@...hat.com>,
        "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, Zeal Robot <zealci@....com.cn>
Subject: Re: [PATCH linux] ext4: Delete useless ret assignment

On 22/01/06 04:59PM, harshad shirwadkar wrote:
> 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
> > >

Since I was also suspecting a similar issue in ext4_fc_record_modified_inode()
(w.r.t. krealloc()) while doing some code reviews a while ago.
And I also happened to stumble upon this discussion which added some more
context to it.

@Luo,
I am preparing some other fixes and might submit this fix also as part of those.
I am completely ok, if you would like to push a patch from your end
based on this discussion. In that case, I will request to drop my patch
or won't even publish it, if you submit it before my fixes gets out.

-ritesh

> > > 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
> > > >
> > > >
> > >
> >