CVE-2021-47656

HIGH EPSS 14.5%
Published Feb 26, 20251y ago · Modified Jun 17, 20261w ago
7.8 CVSS 3.1
High
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Published Feb 26, 2025 1y ago
Last Modified Jun 17, 2026 1w ago

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.

CVSS Details

Base Score
7.8
Exploitability
1.8
Impact
5.9
Vector string
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Attack Vector Local
Attack Complexity Low
Privileges Required Low
User Interaction None
Scope Unchanged
Confidentiality High
Integrity High
Availability High

Threat Intelligence

EPSS Exploit Probability
14.5% percentile
Exploit & Patch Status
No Known Exploit
Patch Available

Weaknesses 1

CWE-416 Use After Free Memory Safety

Affected Products 8

VendorProductVersionRange
linuxlinux_kernel*≥2.6.18  –  <4.9.311
linuxlinux_kernel*≥4.10  –  <4.14.276
linuxlinux_kernel*≥4.15  –  <4.19.238
linuxlinux_kernel*≥4.20  –  <5.4.189
linuxlinux_kernel*≥5.5  –  <5.10.110
linuxlinux_kernel*≥5.11  –  <5.15.33
linuxlinux_kernel*≥5.16  –  <5.16.19
linuxlinux_kernel*≥5.17  –  <5.17.2

References 9

  • git.kernel.org https://git.kernel.org/stable/c/22327bd7988f21de3a53c1373f3b81542bfe1f44
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/30bf7244acf32f19cb722c39f7bc1c2a9f300422
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/3bd2454162ec6bbb5503233c804fce6e4b6dcec5
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/4c7c44ee1650677fbe89d86edbad9497b7679b5c
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/7a75740206af5f17e9f3efa384211cba70213da1
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/7bb7428dd73991bf4b3a7a61b493ca50046c2b13
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/8c0f024f29e055840a5a89fe23b96ae3f921afed
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/9150cb625b46f68d524f4cfd491f1aafc23e10a9
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/c3b07c875fa8f906f932976460fd14798596f101
    Patch

Remediation

  • git.kernel.org https://git.kernel.org/stable/c/22327bd7988f21de3a53c1373f3b81542bfe1f44
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/30bf7244acf32f19cb722c39f7bc1c2a9f300422
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/3bd2454162ec6bbb5503233c804fce6e4b6dcec5
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/4c7c44ee1650677fbe89d86edbad9497b7679b5c
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/7a75740206af5f17e9f3efa384211cba70213da1
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/7bb7428dd73991bf4b3a7a61b493ca50046c2b13
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/8c0f024f29e055840a5a89fe23b96ae3f921afed
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/9150cb625b46f68d524f4cfd491f1aafc23e10a9
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/c3b07c875fa8f906f932976460fd14798596f101
    Patch