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CVE Record

CVE-2021-47649: udmabuf: validate ubuf->pagecount

In the Linux kernel, the following vulnerability has been resolved: udmabuf: validate ubuf->pagecount Syzbot has reported GPF in sg_alloc_append_table_from_pages(). The problem was in ubuf->pages == ZERO_PTR. ubuf->pagecount is calculated from arguments passed from user-space. If user creates udmabuf with list.size == 0 then ubuf->pagecount will be also equal to zero; it causes kmalloc_array() to return ZERO_PTR. Fix it by validating ubuf->pagecount before passing it to kmalloc_array().

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

CVE-2021-47649 is a Linux kernel udmabuf bug triggered by invalid zero-size input from user space. The source reports a general protection fault, indicating possible system instability or crash. No CVSS score, CWE, or active exploitation evidence is provided.

Executive priority

Treat this as a kernel stability exposure with incomplete severity data. Patch through normal kernel maintenance, but accelerate where untrusted local users, containers, or shared workloads exist because the described failure occurs inside kernel memory handling.

Technical view

The kernel calculated ubuf->pagecount from user-space arguments. With list.size equal to zero, pagecount became zero, causing kmalloc_array() to return ZERO_PTR. That invalid pages pointer later reached sg_alloc_append_table_from_pages(), where syzbot observed a general protection fault. The fix validates pagecount before allocation.

Likely exposure

Exposure is limited to Linux systems with affected kernel code and reachable udmabuf functionality. The provided record lists Linux kernel involvement and stable kernel fix commits, but does not identify distributions, configurations, or package names.

Exploitation context

The record attributes discovery to syzbot and describes a user-space supplied zero-size list causing a kernel fault. It does not cite public exploitation, CISA KEV listing, exploit maturity, privilege requirements, or real-world incidents.

Researcher notes

The source evidence supports a bounds/validation flaw around zero pagecount handling in udmabuf. Impact should not be expanded beyond the reported general protection fault without additional vendor analysis. The affected-version data is sparse, so validation should rely on commit presence or distro backports.

Mitigation direction

  • Update to a kernel containing the referenced udmabuf pagecount validation fix.
  • Use Linux distribution advisories because kernel fixes are often backported.
  • Prioritize shared, multi-user, container-host, and workload-dense Linux systems.
  • Check vendor guidance if exact fixed package versions are unclear.

Validation and detection

  • Inventory Linux kernel versions across servers, hosts, and appliances.
  • Confirm whether the udmabuf fix commit is present or backported.
  • Check distribution CVE metadata for CVE-2021-47649 package status.
  • Verify whether udmabuf functionality is enabled or reachable on relevant systems.
Prepared
Confidence
medium
Sources
8

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

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CVE-2021-47649 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
3Timeline events
0ADP providers
7Source links

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxfbb0de795078190a9834b3409e4b009cfb18a6d4, fbb0de795078190a9834b3409e4b009cfb18a6d4, fbb0de795078190a9834b3409e4b009cfb18a6d4, fbb0de795078190a9834b3409e4b009cfb18a6d4, fbb0de795078190a9834b3409e4b009cfb18a6d4, fbb0de795078190a9834b3409e4b009cfb18a6d4unaffected
LinuxLinux4.20, 0, 5.4.189, 5.10.110, 5.15.33, 5.16.19, 5.17.2, 5.18affected
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.