Re: [PATCH] security/keys: fix slab-out-of-bounds in key_task_permission

[chenridong]

On 2024/10/8 7:15, Jarkko Sakkinen wrote:
> Hi,
>
> Revisit...
>
> On Fri, 2024-09-13 at 07:09 +0000, Chen Ridong wrote:
> > We meet the same issue with the LINK, which reads memory out of
> > bounds:
>
> Never ever use pronoun "we" in a commit message in any possible
> sentence. Instead always use passive imperative.
>
> What you probably want to say is:
>
> "KASAN reports an out of bounds read:"
>
> Right?

Yes.

> > BUG: KASAN: slab-out-of-bounds in __kuid_val
> > include/linux/uidgid.h:36
> > BUG: KASAN: slab-out-of-bounds in uid_eq include/linux/uidgid.h:63
> > [inline]
> > BUG: KASAN: slab-out-of-bounds in key_task_permission+0x394/0x410
> > security/keys/permission.c:54
> > Read of size 4 at addr ffff88813c3ab618 by task stress-ng/4362
> >
> > CPU: 2 PID: 4362 Comm: stress-ng Not tainted 5.10.0-14930-
> > gafbffd6c3ede #15
> > Call Trace:
> >   __dump_stack lib/dump_stack.c:82 [inline]
> >   dump_stack+0x107/0x167 lib/dump_stack.c:123
> >   print_address_description.constprop.0+0x19/0x170
> > mm/kasan/report.c:400
> >   __kasan_report.cold+0x6c/0x84 mm/kasan/report.c:560
> >   kasan_report+0x3a/0x50 mm/kasan/report.c:585
> >   __kuid_val include/linux/uidgid.h:36 [inline]
> >   uid_eq include/linux/uidgid.h:63 [inline]
> >   key_task_permission+0x394/0x410 security/keys/permission.c:54
> >   search_nested_keyrings+0x90e/0xe90 security/keys/keyring.c:793
>
> Snip all below away:
>
> >   keyring_search_rcu+0x1b6/0x310 security/keys/keyring.c:922
> >   search_cred_keyrings_rcu+0x111/0x2e0
> > security/keys/process_keys.c:459
> >   search_process_keyrings_rcu+0x1d/0x310
> > security/keys/process_keys.c:544
> >   lookup_user_key+0x782/0x12e0 security/keys/process_keys.c:762
> >   keyctl_invalidate_key+0x20/0x190 security/keys/keyctl.c:434
> >   __do_sys_keyctl security/keys/keyctl.c:1978 [inline]
> >   __se_sys_keyctl+0x1de/0x5b0 security/keys/keyctl.c:1880
> >   do_syscall_64+0x30/0x40 arch/x86/entry/common.c:46
> >   entry_SYSCALL_64_after_hwframe+0x67/0xd1
>
> Remember to cut only the relevant part of the stack trace to make this
> commit message more compact and readable.
Thank you, I will do that.

> > However, we can't reproduce this issue.
> > After our analysis, it can make this issue by following steps.
> > 1.As syzkaller reported, the memory is allocated for struct
>
> "1."
>
> >    assoc_array_shortcut in the assoc_array_insert_into_terminal_node
> >    functions.
> > 2.In the search_nested_keyrings, when we go through the slots in a
> > node,
> >    (bellow tag ascend_to_node), and the slot ptr is meta and
> >    node->back_pointer != NULL, we will proceed to  descend_to_node.
> >    However, there is an exception. If node is the root, and one of the
> >    slots points to a shortcut, it will be treated as a keyring.
> > 3.Whether the ptr is keyring decided by keyring_ptr_is_keyring
> > function.
> >    However, KEYRING_PTR_SUBTYPE is 0x2UL, the same as
> >    ASSOC_ARRAY_PTR_SUBTYPE_MASK,
> > 4.As mentioned above, If a slot of the root is a shortcut, it may be
> >    mistakenly be transferred to a key*, leading to an read out-of-
> > bounds
> >    read.
>
> Delete the whole list and write a description of the problem and why
> your change resolves it.
>
> As per code change, let's layout it something more readable first:
>
> /* Traverse branches into depth: */
> if (assoc_array_ptr_is_meta(ptr)) {
> 	if (node->back_pointer || assoc_array_ptr_is_shortcut(ptr))
> 		goto descend_to_node;
> }
>
> So one thing that should be explained just to make the description
> rigid is why 'ptr' is passed to assoc_array_ptr_is_shortcut() and
> not 'node'. I'm actually 100% sure about that part, which kind
> of supports my view here, right? :-)
>
> The first part of the if-statement obviously filters out everything
> that is not root (when it comes to 'node'). Explain the second part.
> At that point it is know that node is a root node, so continue from
> there.
>
> BR, Jarkko

Thank you for your patience.
I will update soon.

Best regards,
Ridong