CVE-2025-40124

Technical Description

In the Linux kernel, the following vulnerability has been resolved:

sparc: fix accurate exception reporting in copy_{from_to}_user for UltraSPARC III

Anthony Yznaga tracked down that a BUG_ON in ext4 code with large folios

enabled resulted from copy_from_user() returning impossibly large values

greater than the size to be copied. This lead to __copy_from_iter()

returning impossible values instead of the actual number of bytes it was

able to copy.

The BUG_ON has been reported in

https://lore.kernel.org/r/b14f55642207e63e907965e209f6323a0df6dcee.camel@physik.fu-berlin.de

The referenced commit introduced exception handlers on user-space memory

references in copy_from_user and copy_to_user. These handlers return from

the respective function and calculate the remaining bytes left to copy

using the current register contents. The exception handlers expect that

%o2 has already been masked during the bulk copy loop, but the masking was

performed after that loop. This will fix the return val

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References