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

[Jarkko Sakkinen]

On Tue, 2024-10-08 at 09:40 +0800, chenridong wrote:
> 
> 
> 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.

Yeah of course, and I did low quality job earlier no issues admitting
that, so let's do this correct this time. I just try to describe
what I'm seeing as accurately as I can :-) 

Here it is just important to get the explanation and the code change
in-sync so that it is easy to verify and compare them, given that it
is quite sensitive functionality and somewhat obfuscated peace of code
showing age. 

Also I think a good is to make sure that every fix will leave it at
least a bit cleaner state. From this basis I proposed a bit different
layout for the code.

> 
> Best regards,
> Ridong

BR,Jarkko