CVE-2022-50487
Description
A buffer management flaw was found in the Linux kernel's NFS server implementation in the NFSv3 READDIR operation handling. A remote client can trigger this issue by crafting an RPC call with an oversized RPC record header, which forces the server to shrink its response buffer allocation. This causes the READDIR response construction to write beyond the available buffer space, resulting in a send buffer overflow that leads to memory corruption, denial of service via crash, or potential data integrity issues.
Statement
NFSD optimizes memory usage by sharing the same page array for both receiving RPC calls and sending replies, since operations typically don't need large buffers simultaneously. When an RPC call arrives, the response buffer size is calculated based on remaining pages after accounting for the received data. A malicious client can send a correctly-formed but deliberately oversized RPC record containing a small actual RPC call. The NFSD thread processes this normally, but the response buffer (rq_res) is now constrained. When constructing a READDIR reply, which can be quite large, the encoder writes past the truncated buffer boundary into adjacent kernel memory.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.5 | N/A | N/A |
| Attack Vector | Network | N/A | N/A |
| Attack Complexity | Low | N/A | N/A |
| Privileges Required | None | N/A | N/A |
| User Interaction | None | N/A | N/A |
| Scope | Unchanged | N/A | N/A |
| Confidentiality | None | N/A | N/A |
| Integrity Impact | None | N/A | N/A |
| Availability Impact | High | N/A | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Integrity,Availability,Confidentiality
Technical Impact: DoS: Crash, Exit, or Restart; Execute Unauthorized Code or Commands; Read Memory; Modify Memory
If the incorrect calculation is used in the context of memory allocation, then the software may create a buffer that is smaller or larger than expected. If the allocated buffer is smaller than expected, this could lead to an out-of-bounds read or write (CWE-119), possibly causing a crash, allowing arbitrary code execution, or exposing sensitive data.
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