Bug 2400061 (CVE-2025-39793)

Summary: CVE-2025-39793 kernel: io_uring/memmap: cast nr_pages to size_t before shifting
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Version: unspecifiedKeywords: Security
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OS: Linux   
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Description OSIDB Bzimport 2025-09-29 07:02:15 UTC 
In the Linux kernel, the following vulnerability has been resolved:

io_uring/memmap: cast nr_pages to size_t before shifting

If the allocated size exceeds UINT_MAX, then it's necessary to cast
the mr->nr_pages value to size_t to prevent it from overflowing. In
practice this isn't much of a concern as the required memory size will
have been validated upfront, and accounted to the user. And > 4GB sizes
will be necessary to make the lack of a cast a problem, which greatly
exceeds normal user locked_vm settings that are generally in the kb to
mb range. However, if root is used, then accounting isn't done, and
then it's possible to hit this issue.
Comment 1 Jon Moroney 2025-09-29 18:04:18 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025091223-CVE-2025-39793-9d74@gregkh/T