Re: [PATCH] hfs/hfsplus: fix slab-out-of-bounds in hfs_bnode_read_key

[Cengiz Can]

On 24-03-25 09:17:05, Greg KH wrote:
> On Mon, Mar 24, 2025 at 07:14:07PM +0300, Cengiz Can wrote:
> > On 20-03-25 20:30:15, Salvatore Bonaccorso wrote:
> > > Hi
> > > 
> > 
> > Hello Salvatore,
> > 
> > > On Sat, Oct 19, 2024 at 10:13:03PM +0300, Vasiliy Kovalev wrote:
> > > > Syzbot reported an issue in hfs subsystem:
> > > > 
> > > > BUG: KASAN: slab-out-of-bounds in memcpy_from_page include/linux/highmem.h:423 [inline]
> > > > BUG: KASAN: slab-out-of-bounds in hfs_bnode_read fs/hfs/bnode.c:35 [inline]
> > > > BUG: KASAN: slab-out-of-bounds in hfs_bnode_read_key+0x314/0x450 fs/hfs/bnode.c:70
> > > > Write of size 94 at addr ffff8880123cd100 by task syz-executor237/5102
> > > > 
> > > > Call Trace:
> > > >  <TASK>
> > > >  __dump_stack lib/dump_stack.c:94 [inline]
> > > >  dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
> > > >  print_address_description mm/kasan/report.c:377 [inline]
> > > >  print_report+0x169/0x550 mm/kasan/report.c:488
> > > >  kasan_report+0x143/0x180 mm/kasan/report.c:601
> > > >  kasan_check_range+0x282/0x290 mm/kasan/generic.c:189
> > > >  __asan_memcpy+0x40/0x70 mm/kasan/shadow.c:106
> > > >  memcpy_from_page include/linux/highmem.h:423 [inline]
> > > >  hfs_bnode_read fs/hfs/bnode.c:35 [inline]
> > > >  hfs_bnode_read_key+0x314/0x450 fs/hfs/bnode.c:70
> > > >  hfs_brec_insert+0x7f3/0xbd0 fs/hfs/brec.c:159
> > > >  hfs_cat_create+0x41d/0xa50 fs/hfs/catalog.c:118
> > > >  hfs_mkdir+0x6c/0xe0 fs/hfs/dir.c:232
> > > >  vfs_mkdir+0x2f9/0x4f0 fs/namei.c:4257
> > > >  do_mkdirat+0x264/0x3a0 fs/namei.c:4280
> > > >  __do_sys_mkdir fs/namei.c:4300 [inline]
> > > >  __se_sys_mkdir fs/namei.c:4298 [inline]
> > > >  __x64_sys_mkdir+0x6c/0x80 fs/namei.c:4298
> > > >  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> > > >  do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
> > > >  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> > > > RIP: 0033:0x7fbdd6057a99
> > > > 
> > > > Add a check for key length in hfs_bnode_read_key to prevent
> > > > out-of-bounds memory access. If the key length is invalid, the
> > > > key buffer is cleared, improving stability and reliability.
> > > > 
> > > > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> > > > Reported-by: syzbot+5f3a973ed3dfb85a6683@xxxxxxxxxxxxxxxxxxxxxxxxx
> > > > Closes: https://syzkaller.appspot.com/bug?extid=5f3a973ed3dfb85a6683
> > > > Cc: stable@xxxxxxxxxxxxxxx
> > > > Signed-off-by: Vasiliy Kovalev <kovalev@xxxxxxxxxxxx>
> > > > ---
> > > >  fs/hfs/bnode.c     | 6 ++++++
> > > >  fs/hfsplus/bnode.c | 6 ++++++
> > > >  2 files changed, 12 insertions(+)
> > > > 
> > > > diff --git a/fs/hfs/bnode.c b/fs/hfs/bnode.c
> > > > index 6add6ebfef8967..cb823a8a6ba960 100644
> > > > --- a/fs/hfs/bnode.c
> > > > +++ b/fs/hfs/bnode.c
> > > > @@ -67,6 +67,12 @@ void hfs_bnode_read_key(struct hfs_bnode *node, void *key, int off)
> > > >  	else
> > > >  		key_len = tree->max_key_len + 1;
> > > >  
> > > > +	if (key_len > sizeof(hfs_btree_key) || key_len < 1) {
> > > > +		memset(key, 0, sizeof(hfs_btree_key));
> > > > +		pr_err("hfs: Invalid key length: %d\n", key_len);
> > > > +		return;
> > > > +	}
> > > > +
> > > >  	hfs_bnode_read(node, key, off, key_len);
> > > >  }
> > 
> > Simpler the better. 
> > 
> > Our fix was released back in February. (There are other issues in our attempt I
> > admit).
> > 
> > https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/jammy/commit/?id=2e8d8dffa2e0b5291522548309ec70428be7cf5a
> > 
> > If someone can pick this submission, I will be happy to replace our version.
> 
> any specific reason why you didn't submit this upstream?  Or did that
> happen and it somehow not get picked up?

It was mentioned by the researchers that previous attempts were unanswered. I
didn't question the validity of that statement.

I received excerpts from a private email communication indicating that the
HFSPlus filesystem currently has no maintainers, and that at least one of the
decision-makers does not consider filesystem corruption flaws to be particularly
sensitive.

Re-sharing this publicly on linux-fsdevel probably won't get picked up and would
definitely put Ubuntu users at risk, as we were the only ones shipping the
'enabling' policy lines at org.freedesktop.udisks2.filesystem-mount. 

So I proceeded with downstream fix and we released the fix before announcement
date.

> 
> And why assign a CVE for an issue that is in the mainline kernel, last I
> checked, Canonical was NOT allowed to do that.

This was not ideal, you're right. It should be assigned by kernel.org.

> 
> Please work to revoke that CVE and ask for one properly.

Will do. Thanks.

In the meantime, can we get this fix applied?

> 
> thanks,
> 
> greg k-h