RE: [f2fs-dev] [PATCH] f2fs: avoid overflow when large directory feathure is enabled

[Chao Yu]

Hi changman,

> -----Original Message-----
> From: Changman Lee [mailto:cm224.lee@xxxxxxxxxxx]
> Sent: Tuesday, May 27, 2014 2:23 PM
> To: Chao Yu
> Cc: Jaegeuk Kim; linux-fsdevel@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx
> Subject: Re: [f2fs-dev] [PATCH] f2fs: avoid overflow when large directory feathure is enabled
> 
> Hi, Chao
> Good catch. Please, modify Documentation/filesytems/f2fs.txt

Thank you for reminding me, I will add modification of f2fs.txt in the patch later.

> 
> On Tue, May 27, 2014 at 09:06:52AM +0800, Chao Yu wrote:
> > When large directory feathure is enable, We have one case which could cause
> > overflow in dir_buckets() as following:
> > special case: level + dir_level >= 32 and level < MAX_DIR_HASH_DEPTH / 2.
> >
> > Here we define MAX_DIR_BUCKETS to limit the return value when the condition
> > could trigger potential overflow.
> >
> > Signed-off-by: Chao Yu <chao2.yu@xxxxxxxxxxx>
> > ---
> >  fs/f2fs/dir.c           |    4 ++--
> >  include/linux/f2fs_fs.h |    3 +++
> >  2 files changed, 5 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
> > index c3f1485..966acb0 100644
> > --- a/fs/f2fs/dir.c
> > +++ b/fs/f2fs/dir.c
> > @@ -23,10 +23,10 @@ static unsigned long dir_blocks(struct inode *inode)
> >
> >  static unsigned int dir_buckets(unsigned int level, int dir_level)
> >  {
> > -	if (level < MAX_DIR_HASH_DEPTH / 2)
> > +	if (level + dir_level < MAX_DIR_HASH_DEPTH / 2)
> >  		return 1 << (level + dir_level);
> >  	else
> > -		return 1 << ((MAX_DIR_HASH_DEPTH / 2 + dir_level) - 1);
> > +		return MAX_DIR_BUCKETS;
> >  }
> >
> >  static unsigned int bucket_blocks(unsigned int level)
> > diff --git a/include/linux/f2fs_fs.h b/include/linux/f2fs_fs.h
> > index 8c03f71..ba6f312 100644
> > --- a/include/linux/f2fs_fs.h
> > +++ b/include/linux/f2fs_fs.h
> > @@ -394,6 +394,9 @@ typedef __le32	f2fs_hash_t;
> >  /* MAX level for dir lookup */
> >  #define MAX_DIR_HASH_DEPTH	63
> >
> > +/* MAX buckets in one level of dir */
> > +#define MAX_DIR_BUCKETS		(1 << ((MAX_DIR_HASH_DEPTH / 2) - 1))
> > +
> >  #define SIZE_OF_DIR_ENTRY	11	/* by byte */
> >  #define SIZE_OF_DENTRY_BITMAP	((NR_DENTRY_IN_BLOCK + BITS_PER_BYTE - 1) / \
> >  					BITS_PER_BYTE)
> > --
> > 1.7.10.4
> >
> >
> >
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