linux-cve-announce - CVE-2021-47656: jffs2: fix use-after-free in jffs2_clear_xattr

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Message-ID: <2025022650-CVE-2021-47656-0abd@gregkh>
Date: Wed, 26 Feb 2025 02:54:07 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2021-47656: jffs2: fix use-after-free in jffs2_clear_xattr_subsystem

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

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

jffs2: fix use-after-free in jffs2_clear_xattr_subsystem

When we mount a jffs2 image, assume that the first few blocks of
the image are normal and contain at least one xattr-related inode,
but the next block is abnormal. As a result, an error is returned
in jffs2_scan_eraseblock(). jffs2_clear_xattr_subsystem() is then
called in jffs2_build_filesystem() and then again in
jffs2_do_fill_super().

Finally we can observe the following report:
 ==================================================================
 BUG: KASAN: use-after-free in jffs2_clear_xattr_subsystem+0x95/0x6ac
 Read of size 8 at addr ffff8881243384e0 by task mount/719

 Call Trace:
  dump_stack+0x115/0x16b
  jffs2_clear_xattr_subsystem+0x95/0x6ac
  jffs2_do_fill_super+0x84f/0xc30
  jffs2_fill_super+0x2ea/0x4c0
  mtd_get_sb+0x254/0x400
  mtd_get_sb_by_nr+0x4f/0xd0
  get_tree_mtd+0x498/0x840
  jffs2_get_tree+0x25/0x30
  vfs_get_tree+0x8d/0x2e0
  path_mount+0x50f/0x1e50
  do_mount+0x107/0x130
  __se_sys_mount+0x1c5/0x2f0
  __x64_sys_mount+0xc7/0x160
  do_syscall_64+0x45/0x70
  entry_SYSCALL_64_after_hwframe+0x44/0xa9

 Allocated by task 719:
  kasan_save_stack+0x23/0x60
  __kasan_kmalloc.constprop.0+0x10b/0x120
  kasan_slab_alloc+0x12/0x20
  kmem_cache_alloc+0x1c0/0x870
  jffs2_alloc_xattr_ref+0x2f/0xa0
  jffs2_scan_medium.cold+0x3713/0x4794
  jffs2_do_mount_fs.cold+0xa7/0x2253
  jffs2_do_fill_super+0x383/0xc30
  jffs2_fill_super+0x2ea/0x4c0
 [...]

 Freed by task 719:
  kmem_cache_free+0xcc/0x7b0
  jffs2_free_xattr_ref+0x78/0x98
  jffs2_clear_xattr_subsystem+0xa1/0x6ac
  jffs2_do_mount_fs.cold+0x5e6/0x2253
  jffs2_do_fill_super+0x383/0xc30
  jffs2_fill_super+0x2ea/0x4c0
 [...]

 The buggy address belongs to the object at ffff8881243384b8
  which belongs to the cache jffs2_xattr_ref of size 48
 The buggy address is located 40 bytes inside of
  48-byte region [ffff8881243384b8, ffff8881243384e8)
 [...]
 ==================================================================

The triggering of the BUG is shown in the following stack:
-----------------------------------------------------------
jffs2_fill_super
  jffs2_do_fill_super
    jffs2_do_mount_fs
      jffs2_build_filesystem
        jffs2_scan_medium
          jffs2_scan_eraseblock        <--- ERROR
        jffs2_clear_xattr_subsystem    <--- free
    jffs2_clear_xattr_subsystem        <--- free again
-----------------------------------------------------------

An error is returned in jffs2_do_mount_fs(). If the error is returned
by jffs2_sum_init(), the jffs2_clear_xattr_subsystem() does not need to
be executed. If the error is returned by jffs2_build_filesystem(), the
jffs2_clear_xattr_subsystem() also does not need to be executed again.
So move jffs2_clear_xattr_subsystem() from 'out_inohash' to 'out_root'
to fix this UAF problem.

The Linux kernel CVE team has assigned CVE-2021-47656 to this issue.


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

	Issue introduced in 2.6.18 with commit aa98d7cf59b5b0764d3502662053489585faf2fe and fixed in 4.9.311 with commit 9150cb625b46f68d524f4cfd491f1aafc23e10a9
	Issue introduced in 2.6.18 with commit aa98d7cf59b5b0764d3502662053489585faf2fe and fixed in 4.14.276 with commit 3bd2454162ec6bbb5503233c804fce6e4b6dcec5
	Issue introduced in 2.6.18 with commit aa98d7cf59b5b0764d3502662053489585faf2fe and fixed in 4.19.238 with commit c3b07c875fa8f906f932976460fd14798596f101
	Issue introduced in 2.6.18 with commit aa98d7cf59b5b0764d3502662053489585faf2fe and fixed in 5.4.189 with commit 30bf7244acf32f19cb722c39f7bc1c2a9f300422
	Issue introduced in 2.6.18 with commit aa98d7cf59b5b0764d3502662053489585faf2fe and fixed in 5.10.110 with commit 7bb7428dd73991bf4b3a7a61b493ca50046c2b13
	Issue introduced in 2.6.18 with commit aa98d7cf59b5b0764d3502662053489585faf2fe and fixed in 5.15.33 with commit 7a75740206af5f17e9f3efa384211cba70213da1
	Issue introduced in 2.6.18 with commit aa98d7cf59b5b0764d3502662053489585faf2fe and fixed in 5.16.19 with commit 22327bd7988f21de3a53c1373f3b81542bfe1f44
	Issue introduced in 2.6.18 with commit aa98d7cf59b5b0764d3502662053489585faf2fe and fixed in 5.17.2 with commit 8c0f024f29e055840a5a89fe23b96ae3f921afed
	Issue introduced in 2.6.18 with commit aa98d7cf59b5b0764d3502662053489585faf2fe and fixed in 5.18 with commit 4c7c44ee1650677fbe89d86edbad9497b7679b5c

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-2021-47656
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/jffs2/fs.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/9150cb625b46f68d524f4cfd491f1aafc23e10a9
	https://git.kernel.org/stable/c/3bd2454162ec6bbb5503233c804fce6e4b6dcec5
	https://git.kernel.org/stable/c/c3b07c875fa8f906f932976460fd14798596f101
	https://git.kernel.org/stable/c/30bf7244acf32f19cb722c39f7bc1c2a9f300422
	https://git.kernel.org/stable/c/7bb7428dd73991bf4b3a7a61b493ca50046c2b13
	https://git.kernel.org/stable/c/7a75740206af5f17e9f3efa384211cba70213da1
	https://git.kernel.org/stable/c/22327bd7988f21de3a53c1373f3b81542bfe1f44
	https://git.kernel.org/stable/c/8c0f024f29e055840a5a89fe23b96ae3f921afed
	https://git.kernel.org/stable/c/4c7c44ee1650677fbe89d86edbad9497b7679b5c