Re: [PATCH] hfs: Fix OOB Write in hfs_asc2mac

[zhangpeng (AS)]

On 2022/11/30 3:08, Viacheslav Dubeyko wrote:
> > On Nov 28, 2022, at 6:23 PM, zhangpeng (AS) <zhangpeng362@xxxxxxxxxx> wrote:
> >
> > On 2022/11/29 3:29, Viacheslav Dubeyko wrote:
> > > > On Nov 25, 2022, at 8:36 PM, Peng Zhang <zhangpeng362@xxxxxxxxxx> wrote:
> > > >
> > > > From: ZhangPeng <zhangpeng362@xxxxxxxxxx>
> > > >
> > > > Syzbot reported a OOB Write bug:
> > > >
> > > > loop0: detected capacity change from 0 to 64
> > > > ==================================================================
> > > > BUG: KASAN: slab-out-of-bounds in hfs_asc2mac+0x467/0x9a0
> > > > fs/hfs/trans.c:133
> > > > Write of size 1 at addr ffff88801848314e by task syz-executor391/3632
> > > >
> > > > Call Trace:
> > > > <TASK>
> > > > __dump_stack lib/dump_stack.c:88 [inline]
> > > > dump_stack_lvl+0x1b1/0x28e lib/dump_stack.c:106
> > > > print_address_description+0x74/0x340 mm/kasan/report.c:284
> > > > print_report+0x107/0x1f0 mm/kasan/report.c:395
> > > > kasan_report+0xcd/0x100 mm/kasan/report.c:495
> > > > hfs_asc2mac+0x467/0x9a0 fs/hfs/trans.c:133
> > > > hfs_cat_build_key+0x92/0x170 fs/hfs/catalog.c:28
> > > > hfs_lookup+0x1ab/0x2c0 fs/hfs/dir.c:31
> > > > lookup_open fs/namei.c:3391 [inline]
> > > > open_last_lookups fs/namei.c:3481 [inline]
> > > > path_openat+0x10e6/0x2df0 fs/namei.c:3710
> > > > do_filp_open+0x264/0x4f0 fs/namei.c:3740
> > > >
> > > > If in->len is much larger than HFS_NAMELEN(31) which is the maximum
> > > > length of an HFS filename, a OOB Write could occur in hfs_asc2mac(). In
> > > > that case, when the dst reaches the boundary, the srclen is still
> > > > greater than 0, which causes a OOB Write.
> > > > Fix this by adding a Check on dstlen before Writing to dst address.
> > > >
> > > > Fixes: 328b92278650 ("[PATCH] hfs: NLS support")
> > > > Reported-by: syzbot+dc3b1cf9111ab5fe98e7@xxxxxxxxxxxxxxxxxxxxxxxxx
> > > > Signed-off-by: ZhangPeng <zhangpeng362@xxxxxxxxxx>
> > > > ---
> > > > fs/hfs/trans.c | 2 ++
> > > > 1 file changed, 2 insertions(+)
> > > >
> > > > diff --git a/fs/hfs/trans.c b/fs/hfs/trans.c
> > > > index 39f5e343bf4d..886158db07b3 100644
> > > > --- a/fs/hfs/trans.c
> > > > +++ b/fs/hfs/trans.c
> > > > @@ -130,6 +130,8 @@ void hfs_asc2mac(struct super_block *sb, struct hfs_name *out, const struct qstr
> > > > 				dst += size;
> > > > 				dstlen -= size;
> > > > 			} else {
> > > > +				if (dstlen == 0)
> > > > +					goto out;
> > > Maybe, it makes sense to use dstlen instead of srclen in while()?
> > >
> > > We have now:
> > >
> > > while (srclen > 0) {
> > >     <skipped>
> > > } else {
> > >     <skipped>
> > > }
> > >
> > > We can use instead:
> > >
> > > while (dstlen > 0) {
> > >     <skipped>
> > > } else {
> > >     <skipped>
> > > }
> > >
> > > Will it fix the issue?
> > >
> > > Thanks,
> > > Slava.
> > Thank you for your help.
> >
> > After testing, it fix the issue.
> > Would it be better to add dstlen > 0 instead of replacing srclen > 0 with dstlen > 0?
> > Because there may be dstlen > 0 and srclen <= 0.
> >
> > we can use:
> >
> > while (srclen > 0 && dstlen > 0) {
> >    <skipped>
> > } else {
> >    <skipped>
> > }
> Looks good to me.

Can I put you down as a Reviewed-by or Suggested-by?

Thanks,
Zhang Peng

> Thanks,
> Slava.
>
> > Thanks,
> > Zhang Peng
> >
> > > > 				*dst++ = ch > 0xff ? '?' : ch;
> > > > 				dstlen--;
> > > > 			}
> > > > --
> > > > 2.25.1