linux-cve-announce - CVE-2021-47636: ubifs: Fix read out-of-bounds in ubifs_wbuf_write

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Message-ID: <2025022646-CVE-2021-47636-09a4@gregkh>
Date: Wed, 26 Feb 2025 02:53:47 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2021-47636: ubifs: Fix read out-of-bounds in ubifs_wbuf_write_nolock()

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

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

ubifs: Fix read out-of-bounds in ubifs_wbuf_write_nolock()

Function ubifs_wbuf_write_nolock() may access buf out of bounds in
following process:

ubifs_wbuf_write_nolock():
  aligned_len = ALIGN(len, 8);   // Assume len = 4089, aligned_len = 4096
  if (aligned_len <= wbuf->avail) ... // Not satisfy
  if (wbuf->used) {
    ubifs_leb_write()  // Fill some data in avail wbuf
    len -= wbuf->avail;   // len is still not 8-bytes aligned
    aligned_len -= wbuf->avail;
  }
  n = aligned_len >> c->max_write_shift;
  if (n) {
    n <<= c->max_write_shift;
    err = ubifs_leb_write(c, wbuf->lnum, buf + written,
                          wbuf->offs, n);
    // n > len, read out of bounds less than 8(n-len) bytes
  }

, which can be catched by KASAN:
  =========================================================
  BUG: KASAN: slab-out-of-bounds in ecc_sw_hamming_calculate+0x1dc/0x7d0
  Read of size 4 at addr ffff888105594ff8 by task kworker/u8:4/128
  Workqueue: writeback wb_workfn (flush-ubifs_0_0)
  Call Trace:
    kasan_report.cold+0x81/0x165
    nand_write_page_swecc+0xa9/0x160
    ubifs_leb_write+0xf2/0x1b0 [ubifs]
    ubifs_wbuf_write_nolock+0x421/0x12c0 [ubifs]
    write_head+0xdc/0x1c0 [ubifs]
    ubifs_jnl_write_inode+0x627/0x960 [ubifs]
    wb_workfn+0x8af/0xb80

Function ubifs_wbuf_write_nolock() accepts that parameter 'len' is not 8
bytes aligned, the 'len' represents the true length of buf (which is
allocated in 'ubifs_jnl_xxx', eg. ubifs_jnl_write_inode), so
ubifs_wbuf_write_nolock() must handle the length read from 'buf' carefully
to write leb safely.

Fetch a reproducer in [Link].

The Linux kernel CVE team has assigned CVE-2021-47636 to this issue.


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

	Issue introduced in 2.6.27 with commit 1e51764a3c2ac05a23a22b2a95ddee4d9bffb16d and fixed in 4.19.238 with commit 5343575aa11c5d7044107d59d43f84aec01312b0
	Issue introduced in 2.6.27 with commit 1e51764a3c2ac05a23a22b2a95ddee4d9bffb16d and fixed in 5.4.189 with commit b80ccbec0e4804436c382d7dd60e943c386ed83a
	Issue introduced in 2.6.27 with commit 1e51764a3c2ac05a23a22b2a95ddee4d9bffb16d and fixed in 5.10.110 with commit 07a209fadee7b53b46858538e1177597273862e4
	Issue introduced in 2.6.27 with commit 1e51764a3c2ac05a23a22b2a95ddee4d9bffb16d and fixed in 5.15.33 with commit a7054aaf1909cf40489c0ec1b728fdcf79c751a6
	Issue introduced in 2.6.27 with commit 1e51764a3c2ac05a23a22b2a95ddee4d9bffb16d and fixed in 5.16.19 with commit e09fa5318d51f522e1af4fbaf8f74999355980c8
	Issue introduced in 2.6.27 with commit 1e51764a3c2ac05a23a22b2a95ddee4d9bffb16d and fixed in 5.17.2 with commit 3b7fb89135a20587d57f8877c02e25003e9edbdf
	Issue introduced in 2.6.27 with commit 1e51764a3c2ac05a23a22b2a95ddee4d9bffb16d and fixed in 5.18 with commit 4f2262a334641e05f645364d5ade1f565c85f20b

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-2021-47636
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/ubifs/io.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/5343575aa11c5d7044107d59d43f84aec01312b0
	https://git.kernel.org/stable/c/b80ccbec0e4804436c382d7dd60e943c386ed83a
	https://git.kernel.org/stable/c/07a209fadee7b53b46858538e1177597273862e4
	https://git.kernel.org/stable/c/a7054aaf1909cf40489c0ec1b728fdcf79c751a6
	https://git.kernel.org/stable/c/e09fa5318d51f522e1af4fbaf8f74999355980c8
	https://git.kernel.org/stable/c/3b7fb89135a20587d57f8877c02e25003e9edbdf
	https://git.kernel.org/stable/c/4f2262a334641e05f645364d5ade1f565c85f20b