Bug 2524477 (CVE-2026-80578)

Summary: CVE-2026-80578 kernel: fbdev: core: Fix pointer desynchronization in fb_io_read()
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's fbdev core. A local user could trigger an out-of-bounds read vulnerability in the fb_io_read() function. This occurs due to a pointer desynchronization when handling partial copies from a faulty user buffer, allowing the system to read beyond intended memory boundaries. This could lead to information disclosure or system instability.
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Description OSIDB Bzimport 2026-08-26 14:58:27 UTC 
In the Linux kernel, the following vulnerability has been resolved:

fbdev: core: Fix pointer desynchronization in fb_io_read()

In fb_io_read(), if copy_to_user() performs a partial copy (e.g., due to
a faulty user buffer), the loop adjusts the chunk size 'c' and updates
the remaining 'count'. However, the hardware 'src' pointer has already
been eagerly advanced by the original chunk size.

If the loop is allowed to continue, the read will resume from an
incorrect, over-advanced offset. Since the remaining 'count' was only
decremented by the successful bytes, this desynchronization causes the
next iterations to execute more hardware reads than originally bounded,
eventually leading to out-of-bounds I/O reads.

Fix this by breaking out of the loop immediately upon a partial
copy_to_user(). A partial copy indicates a faulty user buffer, making
subsequent read attempts futile. Breaking out ensures we return the
number of successfully read bytes without risking out-of-bounds hardware
accesses in subsequent mismatched iterations.
Comment 1 gkamathe 2026-08-27 11:00:54 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026082614-CVE-2026-80578-dcae@gregkh/T