[SRU][CVE-2019-14283][X/B/D][PATCH 1/1] floppy: fix out-of-bounds read in copy_buffer

[Khaled Elmously]

Yep - thanks Sam!


On 2019-08-07 12:51:32 , Po-Hsu Lin wrote:
> This will need the patch for CVE-2019-14284 to be landed first.
> https://lists.ubuntu.com/archives/kernel-team/2019-July/102711.html
> 
> On Wed, Aug 7, 2019 at 11:37 AM Khaled Elmously
> <khalid.elmously at canonical.com> wrote:
> >
> > On 2019-08-01 10:45:17 , Connor Kuehl wrote:
> > > From: Denis Efremov <efremov at ispras.ru>
> > >
> > > CVE-2019-14283
> > >
> > > This fixes a global out-of-bounds read access in the copy_buffer
> > > function of the floppy driver.
> > >
> > > The FDDEFPRM ioctl allows one to set the geometry of a disk.  The sect
> > > and head fields (unsigned int) of the floppy_drive structure are used to
> > > compute the max_sector (int) in the make_raw_rw_request function.  It is
> > > possible to overflow the max_sector.  Next, max_sector is passed to the
> > > copy_buffer function and used in one of the memcpy calls.
> > >
> > > An unprivileged user could trigger the bug if the device is accessible,
> > > but requires a floppy disk to be inserted.
> > >
> > > The patch adds the check for the .sect * .head multiplication for not
> > > overflowing in the set_geometry function.
> > >
> > > The bug was found by syzkaller.
> > >
> > > Signed-off-by: Denis Efremov <efremov at ispras.ru>
> > > Tested-by: Willy Tarreau <w at 1wt.eu>
> > > Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
> > > (cherry picked from commit da99466ac243f15fbba65bd261bfc75ffa1532b6)
> > > Signed-off-by: Connor Kuehl <connor.kuehl at canonical.com>
> > > ---
> > >  drivers/block/floppy.c | 6 ++++--
> > >  1 file changed, 4 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
> > > index 42ae1d2d8243..7516fed84ae9 100644
> > > --- a/drivers/block/floppy.c
> > > +++ b/drivers/block/floppy.c
> > > @@ -3236,8 +3236,10 @@ static int set_geometry(unsigned int cmd, struct floppy_struct *g,
> > >       int cnt;
> > >
> > >       /* sanity checking for parameters. */
> > > -     if (g->sect <= 0 ||
> > > -         g->head <= 0 ||
> > > +     if ((int)g->sect <= 0 ||
> > > +         (int)g->head <= 0 ||
> > > +         /* check for overflow in max_sector */
> > > +         (int)(g->sect * g->head) <= 0 ||
> > >           /* check for zero in F_SECT_PER_TRACK */
> > >           (unsigned char)((g->sect << 2) >> FD_SIZECODE(g)) == 0 ||
> > >           g->track <= 0 || g->track > UDP->tracks >> STRETCH(g) ||
> >
> >
> > Hmm...This patch doesn't seem to apply to any of X or B or D.
> >
> > Looks like this patch is the upstream patch exactly but it appears the upstream patch actually needs some (minor?) backport work.
> >
> > Connor, could you please double check?
> >
> > Thanks
> >
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