linux-cve-announce - CVE-2024-53216: nfsd: release svc_expkey/svc_export with rcu

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Message-ID: <2024122732-CVE-2024-53216-ba8b@gregkh>
Date: Fri, 27 Dec 2024 14:53:02 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2024-53216: nfsd: release svc_expkey/svc_export with rcu_work

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

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

nfsd: release svc_expkey/svc_export with rcu_work

The last reference for `cache_head` can be reduced to zero in `c_show`
and `e_show`(using `rcu_read_lock` and `rcu_read_unlock`). Consequently,
`svc_export_put` and `expkey_put` will be invoked, leading to two
issues:

1. The `svc_export_put` will directly free ex_uuid. However,
   `e_show`/`c_show` will access `ex_uuid` after `cache_put`, which can
   trigger a use-after-free issue, shown below.

   ==================================================================
   BUG: KASAN: slab-use-after-free in svc_export_show+0x362/0x430 [nfsd]
   Read of size 1 at addr ff11000010fdc120 by task cat/870

   CPU: 1 UID: 0 PID: 870 Comm: cat Not tainted 6.12.0-rc3+ #1
   Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
   1.16.1-2.fc37 04/01/2014
   Call Trace:
    <TASK>
    dump_stack_lvl+0x53/0x70
    print_address_description.constprop.0+0x2c/0x3a0
    print_report+0xb9/0x280
    kasan_report+0xae/0xe0
    svc_export_show+0x362/0x430 [nfsd]
    c_show+0x161/0x390 [sunrpc]
    seq_read_iter+0x589/0x770
    seq_read+0x1e5/0x270
    proc_reg_read+0xe1/0x140
    vfs_read+0x125/0x530
    ksys_read+0xc1/0x160
    do_syscall_64+0x5f/0x170
    entry_SYSCALL_64_after_hwframe+0x76/0x7e

   Allocated by task 830:
    kasan_save_stack+0x20/0x40
    kasan_save_track+0x14/0x30
    __kasan_kmalloc+0x8f/0xa0
    __kmalloc_node_track_caller_noprof+0x1bc/0x400
    kmemdup_noprof+0x22/0x50
    svc_export_parse+0x8a9/0xb80 [nfsd]
    cache_do_downcall+0x71/0xa0 [sunrpc]
    cache_write_procfs+0x8e/0xd0 [sunrpc]
    proc_reg_write+0xe1/0x140
    vfs_write+0x1a5/0x6d0
    ksys_write+0xc1/0x160
    do_syscall_64+0x5f/0x170
    entry_SYSCALL_64_after_hwframe+0x76/0x7e

   Freed by task 868:
    kasan_save_stack+0x20/0x40
    kasan_save_track+0x14/0x30
    kasan_save_free_info+0x3b/0x60
    __kasan_slab_free+0x37/0x50
    kfree+0xf3/0x3e0
    svc_export_put+0x87/0xb0 [nfsd]
    cache_purge+0x17f/0x1f0 [sunrpc]
    nfsd_destroy_serv+0x226/0x2d0 [nfsd]
    nfsd_svc+0x125/0x1e0 [nfsd]
    write_threads+0x16a/0x2a0 [nfsd]
    nfsctl_transaction_write+0x74/0xa0 [nfsd]
    vfs_write+0x1a5/0x6d0
    ksys_write+0xc1/0x160
    do_syscall_64+0x5f/0x170
    entry_SYSCALL_64_after_hwframe+0x76/0x7e

2. We cannot sleep while using `rcu_read_lock`/`rcu_read_unlock`.
   However, `svc_export_put`/`expkey_put` will call path_put, which
   subsequently triggers a sleeping operation due to the following
   `dput`.

   =============================
   WARNING: suspicious RCU usage
   5.10.0-dirty #141 Not tainted
   -----------------------------
   ...
   Call Trace:
   dump_stack+0x9a/0xd0
   ___might_sleep+0x231/0x240
   dput+0x39/0x600
   path_put+0x1b/0x30
   svc_export_put+0x17/0x80
   e_show+0x1c9/0x200
   seq_read_iter+0x63f/0x7c0
   seq_read+0x226/0x2d0
   vfs_read+0x113/0x2c0
   ksys_read+0xc9/0x170
   do_syscall_64+0x33/0x40
   entry_SYSCALL_64_after_hwframe+0x67/0xd1

Fix these issues by using `rcu_work` to help release
`svc_expkey`/`svc_export`. This approach allows for an asynchronous
context to invoke `path_put` and also facilitates the freeing of
`uuid/exp/key` after an RCU grace period.

The Linux kernel CVE team has assigned CVE-2024-53216 to this issue.


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

	Issue introduced in 4.20 with commit 9ceddd9da13434a5906255c0fc528c385aded283 and fixed in 6.6.64 with commit bd8524148dd8c123334b066faa90590ba2ef8e6f
	Issue introduced in 4.20 with commit 9ceddd9da13434a5906255c0fc528c385aded283 and fixed in 6.11.11 with commit 2e4854599200f4d021df8ae17e69221d7c149f3e
	Issue introduced in 4.20 with commit 9ceddd9da13434a5906255c0fc528c385aded283 and fixed in 6.12.2 with commit ad4363a24a5746b257c0beb5d8cc68f9b62c173f
	Issue introduced in 4.20 with commit 9ceddd9da13434a5906255c0fc528c385aded283 and fixed in 6.13-rc1 with commit f8c989a0c89a75d30f899a7cabdc14d72522bb8d

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-2024-53216
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:
	fs/nfsd/export.c
	fs/nfsd/export.h


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/bd8524148dd8c123334b066faa90590ba2ef8e6f
	https://git.kernel.org/stable/c/2e4854599200f4d021df8ae17e69221d7c149f3e
	https://git.kernel.org/stable/c/ad4363a24a5746b257c0beb5d8cc68f9b62c173f
	https://git.kernel.org/stable/c/f8c989a0c89a75d30f899a7cabdc14d72522bb8d