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

Lukas Czerner
2022-01-06T10:58:58Z

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@gmail.com wrote:
> > From: luo penghao <luo.penghao@zte.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@zte.com.cn>
> > Signed-off-by: luo penghao <luo.penghao@zte.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
> >
> >
>