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SubjectRe: [PATCH 1/4] befs: check allocation_group number before use
On Fri, Aug 12, 2016 at 10:38:58AM +0100, Luis de Bethencourt wrote:
> On 12/08/16 08:26, Salah Triki wrote:
> > On Thu, Aug 11, 2016 at 11:56:16AM +0100, Luis de Bethencourt wrote:
> >> On 10/08/16 23:12, Salah Triki wrote:
> >>> Check that the allocation group number is not greater or equal to the
> >>> number of allocations group in the file system and return BEF_ERR in the
> >>> case of error.
> >>>
> >>> Signed-off-by: Salah Triki <salah.triki@gmail.com>
> >>> ---
> >>> fs/befs/befs.h | 5 +++++
> >>> 1 file changed, 5 insertions(+)
> >>>
> >>> diff --git a/fs/befs/befs.h b/fs/befs/befs.h
> >>> index 55f3ea2..6daf4c4 100644
> >>> --- a/fs/befs/befs.h
> >>> +++ b/fs/befs/befs.h
> >>> @@ -121,6 +121,11 @@ BEFS_I(const struct inode *inode)
> >>> static inline befs_blocknr_t
> >>> iaddr2blockno(struct super_block *sb, const befs_inode_addr *iaddr)
> >>> {
> >>> + if (iaddr->allocation_group >= BEFS_SB(sb)->num_ags) {
> >>> + befs_error(sb, "BEFS: Invalid allocation group %u, max is %u",
> >>> + iaddr->allocation_group, BEFS_SB(sb)->num_ags);
> >>> + return BEFS_ERR;
> >>> + }
> >>> return ((iaddr->allocation_group << BEFS_SB(sb)->ag_shift) +
> >>> iaddr->start);
> >>> }
> >>>
> >>
> >> Hi Salah,
> >>
> >> To understand why would we check for this. When can this error happen? I mean,
> >> when can iaddr2blockno() be called with an out of bounds allocation group?
> >>
> >> Thanks,
> >> Luis
> >
> > Hi Luis,
> >
> > allocation group number is set to blockno >> BEFS_SB(sb)->ag_shift by
> > blockno2iaddr(), so if ag_shift is not valid, an out of bound may occur.
> > By now, thanx to your question ;), I think it's better to check the validity
> > of ag_shift when the superblock is loaded.
> >
> > Nack.
> >
> > Thanx for the question :)
> > Salah
> >
>
> No problem :)
>
> I will assume the Nack covers patch 1 to 3. Since they are all related.
>
> Enjoy the weekend,
> Luis

You too.
Salah

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