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

[zhangpeng (AS)]

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>
}


Thanks,
Zhang Peng

> > 				*dst++ = ch > 0xff ? '?' : ch;
> > 				dstlen--;
> > 			}
> > --
> > 2.25.1