Re: [f2fs-dev] [PATCH] f2fs: validate ACL entry sizes in f2fs_acl_from_disk()

Hi Chao,

Thanks for the review.

I agree with both points. I sent a v2 which wraps the new ACL entry-size
checks in unlikely() and returns -EFSCORRUPTED for malformed on-disk ACL
blobs in f2fs_acl_from_disk().

Thanks,
Zhang Cen

Chao Yu <[email protected]> 于2026年6月11日周四 09:59写道：
>
> On 5/24/26 22:37, Zhang Cen wrote:
> > f2fs_acl_count() only validates the aggregate ACL xattr length. A
> > malformed ACL can still place ACL_USER or ACL_GROUP in a slot that only
> > contains struct f2fs_acl_entry_short bytes, and f2fs_acl_from_disk()
> > then reads entry->e_id before verifying that a full entry fits.
> >
> > Require a short entry before reading e_tag and e_perm, and require a
> > full entry before reading e_id for ACL_USER and ACL_GROUP. This keeps
> > corrupted ACL xattrs on the existing -EINVAL path without reading past
> > the copied xattr value.
> >
> > Validation reproduced this kernel report:
> > KASAN slab-out-of-bounds in __f2fs_get_acl+0x6fb/0x7e0
> > RIP: 0033:0x7f4b835ea7aa
> > The buggy address belongs to the object at ffff888114589960 which belongs
> > to the cache kmalloc-8 of size 8
> > The buggy address is located 0 bytes to the right of allocated 8-byte
> > region [ffff888114589960, ffff888114589968)
> > Read of size 4
> > Call trace:
> >   dump_stack_lvl+0x66/0xa0 (?:?)
> >   print_report+0xce/0x630 (?:?)
> >   __f2fs_get_acl+0x6fb/0x7e0 (fs/f2fs/acl.c:169)
> >   srso_alias_return_thunk+0x5/0xfbef5 (?:?)
> >   __virt_addr_valid+0x224/0x430 (?:?)
> >   kasan_report+0xe0/0x110 (?:?)
> >   __f2fs_get_acl+0x5/0x7e0 (fs/f2fs/acl.c:169)
> >   __get_acl+0x281/0x380 (?:?)
> >   vfs_get_acl+0x10b/0x190 (?:?)
> >   do_get_acl+0x2a/0x410 (?:?)
> >   do_get_acl+0x9/0x410 (?:?)
> >   do_getxattr+0xe8/0x260 (?:?)
> >   filename_getxattr+0xd1/0x140 (?:?)
> >   do_getname+0x2d/0x2d0 (?:?)
> >   path_getxattrat+0x16c/0x200 (?:?)
> >   lock_release+0xc8/0x290 (?:?)
> >   cgroup_update_frozen+0x9d/0x320 (?:?)
> >   lockdep_hardirqs_on_prepare+0xea/0x1a0 (?:?)
> >   trace_hardirqs_on+0x1a/0x170 (?:?)
> >   _raw_spin_unlock_irq+0x28/0x50 (?:?)
> >   do_syscall_64+0x115/0x6a0 (arch/x86/entry/syscall_64.c:87)
> >   entry_SYSCALL_64_after_hwframe+0x77/0x7f (?:?)
> >
> > Fixes: af48b85b8cd3 ("f2fs: add xattr and acl functionalities")
> > Assisted-by: Codex:gpt-5.5
> > Signed-off-by: Zhang Cen <[email protected]>
> > ---
> >  fs/f2fs/acl.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/f2fs/acl.c b/fs/f2fs/acl.c
> > index fa8d81a30fb9..290fee451637 100644
> > --- a/fs/f2fs/acl.c
> > +++ b/fs/f2fs/acl.c
> > @@ -70,7 +70,7 @@ static struct posix_acl *f2fs_acl_from_disk(const char *value, size_t size)
> >
> >       for (i = 0; i < count; i++) {
> >
> > -             if ((char *)entry > end)
> > +             if ((char *)entry + sizeof(struct f2fs_acl_entry_short) > end)
>
> unlikely()?
>
> Should return -EFSCORRUPTED instead of -EINVAL?
>
> >                       goto fail;
> >
> >               acl->a_entries[i].e_tag  = le16_to_cpu(entry->e_tag);
> > @@ -86,6 +86,8 @@ static struct posix_acl *f2fs_acl_from_disk(const char *value, size_t size)
> >                       break;
> >
> >               case ACL_USER:
> > +                     if ((char *)entry + sizeof(struct f2fs_acl_entry) > end)
>
> Ditto,
>
> > +                             goto fail;
> >                       acl->a_entries[i].e_uid =
> >                               make_kuid(&init_user_ns,
> >                                               le32_to_cpu(entry->e_id));
> > @@ -93,6 +95,8 @@ static struct posix_acl *f2fs_acl_from_disk(const char *value, size_t size)
> >                                       sizeof(struct f2fs_acl_entry));
> >                       break;
> >               case ACL_GROUP:
> > +                     if ((char *)entry + sizeof(struct f2fs_acl_entry) > end)
>
> Ditto,
>
> Thanks,
>
> > +                             goto fail;
> >                       acl->a_entries[i].e_gid =
> >                               make_kgid(&init_user_ns,
> >                                               le32_to_cpu(entry->e_id));
>


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