On Wed 14-02-18 18:26:03, Pali Rohár wrote:
> On Wednesday 14 February 2018 11:28:46 Jan Kara wrote:
> > According to ECMA-167 3/8.4.2 Volume Descriptor Pointer is terminating
> > current extent of Volume Descriptor Sequence. Also according to ECMA-167
> > 3/8.4.3 Volume Descriptor Sequence Number is not significant for Volume
> > Descriptor Pointers. Simplify the handling of Volume Descriptor Pointers
> > to take this into account.
> >
> > Signed-off-by: Jan Kara <jack@xxxxxxx>
> > ---
> > fs/udf/super.c | 41 ++++++++++++++++-------------------------
> > 1 file changed, 16 insertions(+), 25 deletions(-)
> >
> > diff --git a/fs/udf/super.c b/fs/udf/super.c
> > index 5c5d5fd513cc..f80b97173acd 100644
> > --- a/fs/udf/super.c
> > +++ b/fs/udf/super.c
> > @@ -1615,7 +1615,6 @@ static noinline int udf_process_sequence(
> > bool done = false;
> > uint32_t vdsn;
> > uint16_t ident;
> > - long next_s = 0, next_e = 0;
> > int ret;
> > unsigned int indirections = 0;
> >
> > @@ -1647,19 +1646,22 @@ static noinline int udf_process_sequence(
> > }
> > break;
> > case TAG_IDENT_VDP: /* ISO 13346 3/10.3 */
> > - curr = &vds[VDS_POS_VOL_DESC_PTR];
> > - if (vdsn >= curr->volDescSeqNum) {
> > - curr->volDescSeqNum = vdsn;
> > - curr->block = block;
> > -
> > - vdp = (struct volDescPtr *)bh->b_data;
> > - next_s = le32_to_cpu(
> > - vdp->nextVolDescSeqExt.extLocation);
> > - next_e = le32_to_cpu(
> > - vdp->nextVolDescSeqExt.extLength);
> > - next_e = next_e >> sb->s_blocksize_bits;
> > - next_e += next_s - 1;
> > + if (++indirections > UDF_MAX_TD_NESTING) {
> > + udf_err(sb, "too many Volume Descriptor "
> > + "Pointers (max %u supported)\n",
> > + UDF_MAX_TD_NESTING);
> > + brelse(bh);
> > + return -EIO;
> > }
> > +
> > + vdp = (struct volDescPtr *)bh->b_data;
> > + block = le32_to_cpu(vdp->nextVolDescSeqExt.extLocation);
>
> Another pathological case: disc with two (or more) VDP descriptors and
> each points to another in cycle.
>
> Seems that this would not cause infinite loop due to
> UDF_MAX_TD_NESTING, but probably can cause some troubles.
Yes. Such disk is invalid so our only goal is not to crash / livelock the
kernel and UDF_MAX_TD_NESTING protection is enough for that.
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
