Re: [PATCH] fs: jfs: fix shift-out-of-bounds in dbAllocAG

[Dongliang Mu]

On Fri, Oct 14, 2022 at 4:55 AM Dave Kleikamp <dave.kleikamp@xxxxxxxxxx> wrote:
>
> On 9/29/22 12:44AM, Dongliang Mu wrote:
> > From: Dongliang Mu <mudongliangabcd@xxxxxxxxx>
> >
> > Syzbot found a crash : UBSAN: shift-out-of-bounds in dbAllocAG. The
> > underlying bug is the missing check of bmp->db_agl2size. The field can
> > be greater than 32 and trigger the shift-out-of-bounds.
>
> The shift is done to a 64-byte value, not 32.
>
> The volume can contain up to 2^43 blocks, which are divided up into 128
> (2^7) aggregate groups, so each AG can have 2^36 blocks, which makes 36
> a valid value for db_agl2size.

Thanks for your explanation. Will send a v2 patch after testing in Syzbot.

>
> >
> > Fix this bug by adding a check of bmp->db_agl2size in dbMount since this
> > field is used in many following functions. Note that, for maintainance,
> > I reorganzie the error handling code of dbMount.
> >
> > Reported-by: syzbot+15342c1aa6a00fb7a438@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Signed-off-by: Dongliang Mu <mudongliangabcd@xxxxxxxxx>
> > ---
> >   fs/jfs/jfs_dmap.c | 21 +++++++++++++++------
> >   1 file changed, 15 insertions(+), 6 deletions(-)
> >
> > diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
> > index 6b838d3ae7c2..4c717f245920 100644
> > --- a/fs/jfs/jfs_dmap.c
> > +++ b/fs/jfs/jfs_dmap.c
> > @@ -155,7 +155,7 @@ int dbMount(struct inode *ipbmap)
> >       struct bmap *bmp;
> >       struct dbmap_disk *dbmp_le;
> >       struct metapage *mp;
> > -     int i;
> > +     int i, err;
> >
> >       /*
> >        * allocate/initialize the in-memory bmap descriptor
> > @@ -170,8 +170,8 @@ int dbMount(struct inode *ipbmap)
> >                          BMAPBLKNO << JFS_SBI(ipbmap->i_sb)->l2nbperpage,
> >                          PSIZE, 0);
> >       if (mp == NULL) {
> > -             kfree(bmp);
> > -             return -EIO;
> > +             err = -EIO;
> > +             goto err_kfree_bmp;
> >       }
> >
> >       /* copy the on-disk bmap descriptor to its in-memory version. */
> > @@ -181,9 +181,8 @@ int dbMount(struct inode *ipbmap)
> >       bmp->db_l2nbperpage = le32_to_cpu(dbmp_le->dn_l2nbperpage);
> >       bmp->db_numag = le32_to_cpu(dbmp_le->dn_numag);
> >       if (!bmp->db_numag) {
> > -             release_metapage(mp);
> > -             kfree(bmp);
> > -             return -EINVAL;
> > +             err = -EINVAL;
> > +             goto err_release_metapage;
> >       }
> >
> >       bmp->db_maxlevel = le32_to_cpu(dbmp_le->dn_maxlevel);
> > @@ -194,6 +193,10 @@ int dbMount(struct inode *ipbmap)
> >       bmp->db_agwidth = le32_to_cpu(dbmp_le->dn_agwidth);
> >       bmp->db_agstart = le32_to_cpu(dbmp_le->dn_agstart);
> >       bmp->db_agl2size = le32_to_cpu(dbmp_le->dn_agl2size);
> > +     if (bmp->db_agl2size >= 32) {
>
> I think the right number here is MAXMAPSIZE - L2MAXAG, so
>
>         if (bmp->db_agl2size > (MAXMAPSIZE - L2MAXAG)) {
>
> > +             err = -EINVAL;
> > +             goto err_release_metapage;
> > +     }
> >       for (i = 0; i < MAXAG; i++)
> >               bmp->db_agfree[i] = le64_to_cpu(dbmp_le->dn_agfree[i]);
> >       bmp->db_agsize = le64_to_cpu(dbmp_le->dn_agsize);
> > @@ -214,6 +217,12 @@ int dbMount(struct inode *ipbmap)
> >       BMAP_LOCK_INIT(bmp);
> >
> >       return (0);
> > +
> > +err_release_metapage:
> > +     release_metapage(mp);
> > +err_kfree_bmp:
> > +     kfree(bmp);
> > +     return err;
> >   }
> >
> >