CVE-2026-46253: pstore/ram: fix buffer overflow in persistent_ram_save_old()

CVE-2026-46253: pstore/ram: fix buffer overflow in persistent_ram_save_old()

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

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

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

pstore/ram: fix buffer overflow in persistent_ram_save_old()

persistent_ram_save_old() can be called multiple times for the same
persistent_ram_zone (e.g., via ramoops_pstore_read -> ramoops_get_next_prz
for PSTORE_TYPE_DMESG records).

Currently, the function only allocates prz->old_log when it is NULL,
but it unconditionally updates prz->old_log_size to the current buffer
size and then performs memcpy_fromio() using this new size. If the
buffer size has grown since the first allocation (which can happen
across different kernel boot cycles), this leads to:

1. A heap buffer overflow (OOB write) in the memcpy_fromio() calls
2. A subsequent OOB read when ramoops_pstore_read() accesses the buffer
   using the incorrect (larger) old_log_size

The KASAN splat would look similar to:
  BUG: KASAN: slab-out-of-bounds in ramoops_pstore_read+0x...
  Read of size N at addr ... by task ...

The conditions are likely extremely hard to hit:

  0. Crash with a ramoops write of less-than-record-max-size bytes.
  1. Reboot: ramoops registers, pstore_get_records(0) reads old crash,
     allocates old_log with size X
  2. Crash handler registered, timer started (if pstore_update_ms >= 0)
  3. Oops happens (non-fatal, system continues)
  4. pstore_dump() writes oops via ramoops_pstore_write() size Y (>X)
  5. pstore_new_entry = 1, pstore_timer_kick() called
  6. System continues running (not a panic oops)
  7. Timer fires after pstore_update_ms milliseconds
  8. pstore_timefunc() → schedule_work() → pstore_dowork() → pstore_get_records(1)
  9. ramoops_get_next_prz() → persistent_ram_save_old()
 10. buffer_size() returns Y, but old_log is X bytes
 11. Y > X: memcpy_fromio() overflows heap

  Requirements:
  - a prior crash record exists that did not fill the record size
    (almost impossible since the crash handler writes as much as it
    can possibly fit into the record, capped by max record size and
    the kmsg buffer almost always exceeds the max record size)
  - pstore_update_ms >= 0 (disabled by default)
  - Non-fatal oops (system survives)

Free and reallocate the buffer when the new size differs from the
previously allocated size. This ensures old_log always has sufficient
space for the data being copied.

The Linux kernel CVE team has assigned CVE-2026-46253 to this issue.


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

	Issue introduced in 3.5 with commit 201e4aca5aa179e6c69a4dcd36a3562e56b8d670 and fixed in 5.10.252 with commit 58bda5a1d1ee98254383ef34f76b2c35140513ea
	Issue introduced in 3.5 with commit 201e4aca5aa179e6c69a4dcd36a3562e56b8d670 and fixed in 5.15.202 with commit 06d2c8bd108cea503f6f6e13e47495ed1085275f
	Issue introduced in 3.5 with commit 201e4aca5aa179e6c69a4dcd36a3562e56b8d670 and fixed in 6.1.165 with commit 2fa9a047c6a50ec80c3890dd623b85e237f0d1fd
	Issue introduced in 3.5 with commit 201e4aca5aa179e6c69a4dcd36a3562e56b8d670 and fixed in 6.6.128 with commit cff0ef043e16feb5a02307c8f9d0117a96c5587c
	Issue introduced in 3.5 with commit 201e4aca5aa179e6c69a4dcd36a3562e56b8d670 and fixed in 6.12.75 with commit 9a6fc69a570c0780834246d52c856cc3dbc2605f
	Issue introduced in 3.5 with commit 201e4aca5aa179e6c69a4dcd36a3562e56b8d670 and fixed in 6.18.14 with commit 4f73486ca822305c1cf5b8ebc0b53a6ab3801a81
	Issue introduced in 3.5 with commit 201e4aca5aa179e6c69a4dcd36a3562e56b8d670 and fixed in 6.19.4 with commit 7cfe964e61c0ab667abd5f5b68e0acbf783efa4f
	Issue introduced in 3.5 with commit 201e4aca5aa179e6c69a4dcd36a3562e56b8d670 and fixed in 7.0 with commit 5669645c052f235726a85f443769b6fc02f66762

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-2026-46253
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/pstore/ram_core.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/58bda5a1d1ee98254383ef34f76b2c35140513ea
	https://git.kernel.org/stable/c/06d2c8bd108cea503f6f6e13e47495ed1085275f
	https://git.kernel.org/stable/c/2fa9a047c6a50ec80c3890dd623b85e237f0d1fd
	https://git.kernel.org/stable/c/cff0ef043e16feb5a02307c8f9d0117a96c5587c
	https://git.kernel.org/stable/c/9a6fc69a570c0780834246d52c856cc3dbc2605f
	https://git.kernel.org/stable/c/4f73486ca822305c1cf5b8ebc0b53a6ab3801a81
	https://git.kernel.org/stable/c/7cfe964e61c0ab667abd5f5b68e0acbf783efa4f
	https://git.kernel.org/stable/c/5669645c052f235726a85f443769b6fc02f66762