Bug 2347642 (CVE-2022-49077)

Summary: CVE-2022-49077 kernel: mmmremap.c: avoid pointless invalidate_range_start/end on mremap(old_size=0)
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: medium    
Version: unspecifiedCC: dfreiber, drow, jburrell, vkumar
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Hardware: All   
OS: Linux   
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Description OSIDB Bzimport 2025-02-26 03:01:27 UTC 
In the Linux kernel, the following vulnerability has been resolved:

mmmremap.c: avoid pointless invalidate_range_start/end on mremap(old_size=0)

If an mremap() syscall with old_size=0 ends up in move_page_tables(), it
will call invalidate_range_start()/invalidate_range_end() unnecessarily,
i.e.  with an empty range.

This causes a WARN in KVM's mmu_notifier.  In the past, empty ranges
have been diagnosed to be off-by-one bugs, hence the WARNing.  Given the
low (so far) number of unique reports, the benefits of detecting more
buggy callers seem to outweigh the cost of having to fix cases such as
this one, where userspace is doing something silly.  In this particular
case, an early return from move_page_tables() is enough to fix the
issue.
Comment 1 Mauro Matteo Cascella 2025-02-26 15:03:29 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025022656-CVE-2022-49077-6e0c@gregkh/T