Re: [PATCH] f2fs: fix use-after-free issue with sbi->stat_info

[Sahitya Tummala <stummala@codeaurora.org>]

On Tue, Dec 25, 2018 at 11:06:45AM +0800, Chao Yu wrote:
> On 2018/12/24 21:06, Sahitya Tummala wrote:
> > iput() on sbi->node_inode can update sbi->stat_info
> > in the below context, if the f2fs_write_checkpoint()
> > has failed with error.
> > 
> > f2fs_balance_fs_bg+0x1ac/0x1ec
> > f2fs_write_node_pages+0x4c/0x260
> > do_writepages+0x80/0xbc
> > __writeback_single_inode+0xdc/0x4ac
> > writeback_single_inode+0x9c/0x144
> > write_inode_now+0xc4/0xec
> > iput+0x194/0x22c
> > f2fs_put_super+0x11c/0x1e8
> > generic_shutdown_super+0x70/0xf4
> > kill_block_super+0x2c/0x5c
> > kill_f2fs_super+0x44/0x50
> > deactivate_locked_super+0x60/0x8c
> > deactivate_super+0x68/0x74
> > cleanup_mnt+0x40/0x78
> > 
> > Fix this by moving f2fs_destroy_stats() further below iput().
> > 
> > Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
> > ---
> >  fs/f2fs/super.c | 9 ++++++---
> >  1 file changed, 6 insertions(+), 3 deletions(-)
> > 
> > diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> > index e184ad4e..df41a3a 100644
> > --- a/fs/f2fs/super.c
> > +++ b/fs/f2fs/super.c
> > @@ -1058,9 +1058,6 @@ static void f2fs_put_super(struct super_block *sb)
> >  		f2fs_write_checkpoint(sbi, &cpc);
> >  	}
> >  
> > -	/* f2fs_write_checkpoint can update stat informaion */
> > -	f2fs_destroy_stats(sbi);
> 
> The code order in error path of fill_super is almost the same as the one of
> put_super, could you please check that as well?
> 

Thanks Chao, for pointing it out. Yes, the same issue exists in error path of
fill_super as well. I will fix it.

> Thanks,
> 
> > -
> >  	/*
> >  	 * normally superblock is clean, so we need to release this.
> >  	 * In addition, EIO will skip do checkpoint, we need this as well.
> > @@ -1080,6 +1077,12 @@ static void f2fs_put_super(struct super_block *sb)
> >  	iput(sbi->node_inode);
> >  	iput(sbi->meta_inode);
> >  
> > +	/*
> > +	 * iput() can update stat information, if f2fs_write_checkpoint()
> > +	 * above failed with error.
> > +	 */
> > +	f2fs_destroy_stats(sbi);
> > +
> >  	/* destroy f2fs internal modules */
> >  	f2fs_destroy_node_manager(sbi);
> >  	f2fs_destroy_segment_manager(sbi);
> > 
> 

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