[PATCH v1] erofs-utils: lib: Fix 8MB bug on uncompressed extent size

[Kelvin Zhang]

friendly ping : )

On Tue, Dec 21, 2021 at 7:21 PM Gao Xiang <hsiangkao at linux.alibaba.com> wrote:
>
> On Tue, Dec 21, 2021 at 06:03:07PM -0800, Kelvin Zhang wrote:
> > Previously, uncompressed extent can be at most 8MB before mkfs.erofs
> > crashes on some error condition. This is due to a minor bug in how
> > compressed indices are encoded. This patch fixes the issue.
> >
> > Signed-off-by: Kelvin Zhang <zhangkelvin at google.com>
>
> I have to hold this for a while and look into (evaluate) that when I
> get a full free time... (maybe a week later.) I understand it's not
> quite urgent for all of us currently..
>
> I still stuck into ztailpacking inline feature for now...
>
> Thanks,
> Gao Xiang
>
> > ---
> >  include/erofs_fs.h |  2 +-
> >  lib/compress.c     | 21 ++++++++++++++++++++-
> >  2 files changed, 21 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/erofs_fs.h b/include/erofs_fs.h
> > index 9a91877..13eaf24 100644
> > --- a/include/erofs_fs.h
> > +++ b/include/erofs_fs.h
> > @@ -353,7 +353,7 @@ enum {
> >   * compressed block count of a compressed extent (in logical clusters, aka.
> >   * block count of a pcluster).
> >   */
> > -#define Z_EROFS_VLE_DI_D0_CBLKCNT            (1 << 11)
> > +#define Z_EROFS_VLE_DI_D0_CBLKCNT            (1U << 11)
> >
> >  struct z_erofs_vle_decompressed_index {
> >       __le16 di_advise;
> > diff --git a/lib/compress.c b/lib/compress.c
> > index 98be7a2..23e571c 100644
> > --- a/lib/compress.c
> > +++ b/lib/compress.c
> > @@ -97,7 +97,26 @@ static void vle_write_indexes(struct z_erofs_vle_compress_ctx *ctx,
> >               } else if (d0) {
> >                       type = Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD;
> >
> > -                     di.di_u.delta[0] = cpu_to_le16(d0);
> > +                     /* If the |Z_EROFS_VLE_DI_D0_CBLKCNT| bit is set, parser
> > +                      * will interpret |delta[0]| as size of pcluster, rather
> > +                      * than distance to last head cluster. Normally this
> > +                      * isn't a problem, because uncompressed extent size are
> > +                      * below Z_EROFS_VLE_DI_D0_CBLKCNT * BLOCK_SIZE = 8MB.
> > +                      * But with large pcluster it's possible to go over this
> > +                      * number, resulting in corrupted compressed indices.
> > +                      * To solve this, we use Z_EROFS_VLE_DI_D0_CBLKCNT-1 if
> > +                      * the uncompressed extent size goes above 8MB. This is
> > +                      * OK because if kernel sees another non-head cluster
> > +                      * after going back by |delta[0]| blocks, kernel will
> > +                      * just keep looking back.
> > +                      */
> > +                     if (d0 & Z_EROFS_VLE_DI_D0_CBLKCNT) {
> > +                             di.di_u.delta[0] = max(
> > +                                     d0 & (~Z_EROFS_VLE_DI_D0_CBLKCNT),
> > +                                     Z_EROFS_VLE_DI_D0_CBLKCNT-1);
> > +                     } else {
> > +                             di.di_u.delta[0] = cpu_to_le16(d0);
> > +                     }
> >                       di.di_u.delta[1] = cpu_to_le16(d1);
> >               } else {
> >                       type = raw ? Z_EROFS_VLE_CLUSTER_TYPE_PLAIN :
> > --
> > 2.34.1.448.ga2b2bfdf31-goog



-- 
Sincerely,

Kelvin Zhang