Message-ID: <2024122700-CVE-2024-56592-d4b2@gregkh>
Date: Fri, 27 Dec 2024 15:50:59 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2024-56592: bpf: Call free_htab_elem() after htab_unlock_bucket()

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

bpf: Call free_htab_elem() after htab_unlock_bucket()

For htab of maps, when the map is removed from the htab, it may hold the
last reference of the map. bpf_map_fd_put_ptr() will invoke
bpf_map_free_id() to free the id of the removed map element. However,
bpf_map_fd_put_ptr() is invoked while holding a bucket lock
(raw_spin_lock_t), and bpf_map_free_id() attempts to acquire map_idr_lock
(spinlock_t), triggering the following lockdep warning:

  =============================
  [ BUG: Invalid wait context ]
  6.11.0-rc4+ #49 Not tainted
  -----------------------------
  test_maps/4881 is trying to lock:
  ffffffff84884578 (map_idr_lock){+...}-{3:3}, at: bpf_map_free_id.part.0+0x21/0x70
  other info that might help us debug this:
  context-{5:5}
  2 locks held by test_maps/4881:
   #0: ffffffff846caf60 (rcu_read_lock){....}-{1:3}, at: bpf_fd_htab_map_update_elem+0xf9/0x270
   #1: ffff888149ced148 (&htab->lockdep_key#2){....}-{2:2}, at: htab_map_update_elem+0x178/0xa80
  stack backtrace:
  CPU: 0 UID: 0 PID: 4881 Comm: test_maps Not tainted 6.11.0-rc4+ #49
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), ...
  Call Trace:
   <TASK>
   dump_stack_lvl+0x6e/0xb0
   dump_stack+0x10/0x20
   __lock_acquire+0x73e/0x36c0
   lock_acquire+0x182/0x450
   _raw_spin_lock_irqsave+0x43/0x70
   bpf_map_free_id.part.0+0x21/0x70
   bpf_map_put+0xcf/0x110
   bpf_map_fd_put_ptr+0x9a/0xb0
   free_htab_elem+0x69/0xe0
   htab_map_update_elem+0x50f/0xa80
   bpf_fd_htab_map_update_elem+0x131/0x270
   htab_map_update_elem+0x50f/0xa80
   bpf_fd_htab_map_update_elem+0x131/0x270
   bpf_map_update_value+0x266/0x380
   __sys_bpf+0x21bb/0x36b0
   __x64_sys_bpf+0x45/0x60
   x64_sys_call+0x1b2a/0x20d0
   do_syscall_64+0x5d/0x100
   entry_SYSCALL_64_after_hwframe+0x76/0x7e

One way to fix the lockdep warning is using raw_spinlock_t for
map_idr_lock as well. However, bpf_map_alloc_id() invokes
idr_alloc_cyclic() after acquiring map_idr_lock, it will trigger a
similar lockdep warning because the slab's lock (s->cpu_slab->lock) is
still a spinlock.

Instead of changing map_idr_lock's type, fix the issue by invoking
htab_put_fd_value() after htab_unlock_bucket(). However, only deferring
the invocation of htab_put_fd_value() is not enough, because the old map
pointers in htab of maps can not be saved during batched deletion.
Therefore, also defer the invocation of free_htab_elem(), so these
to-be-freed elements could be linked together similar to lru map.

There are four callers for ->map_fd_put_ptr:

(1) alloc_htab_elem() (through htab_put_fd_value())
It invokes ->map_fd_put_ptr() under a raw_spinlock_t. The invocation of
htab_put_fd_value() can not simply move after htab_unlock_bucket(),
because the old element has already been stashed in htab->extra_elems.
It may be reused immediately after htab_unlock_bucket() and the
invocation of htab_put_fd_value() after htab_unlock_bucket() may release
the newly-added element incorrectly. Therefore, saving the map pointer
of the old element for htab of maps before unlocking the bucket and
releasing the map_ptr after unlock. Beside the map pointer in the old
element, should do the same thing for the special fields in the old
element as well.

(2) free_htab_elem() (through htab_put_fd_value())
Its caller includes __htab_map_lookup_and_delete_elem(),
htab_map_delete_elem() and __htab_map_lookup_and_delete_batch().

For htab_map_delete_elem(), simply invoke free_htab_elem() after
htab_unlock_bucket(). For __htab_map_lookup_and_delete_batch(), just
like lru map, linking the to-be-freed element into node_to_free list
and invoking free_htab_elem() for these element after unlock. It is safe
to reuse batch_flink as the link for node_to_free, because these
elements have been removed from the hash llist.

Because htab of maps doesn't support lookup_and_delete operation,
__htab_map_lookup_and_delete_elem() doesn't have the problem, so kept
it as is.

(3) fd_htab_map_free()
It invokes ->map_fd_put_ptr without raw_spinlock_t.

(4) bpf_fd_htab_map_update_elem()
It invokes ->map_fd_put_ptr without raw_spinlock_t.

After moving free_htab_elem() outside htab bucket lock scope, using
pcpu_freelist_push() instead of __pcpu_freelist_push() to disable
the irq before freeing elements, and protecting the invocations of
bpf_mem_cache_free() with migrate_{disable|enable} pair.

The Linux kernel CVE team has assigned CVE-2024-56592 to this issue.


Affected and fixed versions
===========================

	Fixed in 6.6.66 with commit 10e8a2dec9ff1b81de8e892b0850924038adbc6d
	Fixed in 6.12.5 with commit a50b4aa3007e63a590d501341f304676ebc74b3b
	Fixed in 6.13-rc1 with commit b9e9ed90b10c82a4e9d4d70a2890f06bfcdd3b78

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2024-56592
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	kernel/bpf/hashtab.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/10e8a2dec9ff1b81de8e892b0850924038adbc6d
	https://git.kernel.org/stable/c/a50b4aa3007e63a590d501341f304676ebc74b3b
	https://git.kernel.org/stable/c/b9e9ed90b10c82a4e9d4d70a2890f06bfcdd3b78

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