On Thu, Aug 04, 2022 at 05:31:39PM +0100, Robin Murphy wrote:
> On 04/08/2022 3:32 pm, Dan Carpenter wrote:
> > There are two issues here:
> >
> > 1) The "len" variable needs to be checked before the very first write.
> > Otherwise if omap2_iommu_dump_ctx() with "bytes" less than 32 it is a
> > buffer overflow.
> > 2) The snprintf() function returns the number of bytes that *would* have
> > been copied if there were enough space. But we want to know the
> > number of bytes which were *actually* copied so use scnprintf()
> > instead.
> >
> > Fixes: bd4396f09a4a ("iommu/omap: Consolidate OMAP IOMMU modules")
>
> FWIW I think this has actually been broken since day one back in
> 14e0e6796a0d, but I'm also not inclined to care that much - 2014 is already
> plenty long ago.
>
I don't know how I didn't see that. It's like my eyeballs are broken
sometimes. Possibly it should be:
Fixes: 14e0e6796a0d ("OMAP: iommu: add initial debugfs support")
Althought that's debatable as well...
> > Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> > ---
> > drivers/iommu/omap-iommu-debug.c | 6 +++---
> > 1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/iommu/omap-iommu-debug.c b/drivers/iommu/omap-iommu-debug.c
> > index a99afb5d9011..259f65291d90 100644
> > --- a/drivers/iommu/omap-iommu-debug.c
> > +++ b/drivers/iommu/omap-iommu-debug.c
> > @@ -32,12 +32,12 @@ static inline bool is_omap_iommu_detached(struct omap_iommu *obj)
> > ssize_t bytes; \
> > const char *str = "%20s: %08x\n"; \
> > const int maxcol = 32; \
> > - bytes = snprintf(p, maxcol, str, __stringify(name), \
> > + if (len < maxcol) \
> > + goto out; \
> > + bytes = scnprintf(p, maxcol, str, __stringify(name), \
> > iommu_read_reg(obj, MMU_##name)); \
>
> I suppose snprintf is OK in practice since none of the names are anywhere
> near 20 characters long anyway, but I agree it's better to be obviously
> foolproof.
The issue with scnprintf() vs snprintf() is not the 32 character limit.
The issue is the "p - buf" math in omap2_iommu_dump_ctx(). The "p"
variable is past the end of the buffer. The user decides the size of
the buffer so it's a real bug.
regards,
dan carpenter
