CVE-2025-39840audit: fix out-of-bounds read in audit_compare_dname_path()

Official description

In the Linux kernel, the following vulnerability has been resolved: audit: fix out-of-bounds read in audit_compare_dname_path() When a watch on dir=/ is combined with an fsnotify event for a single-character name directly under / (e.g., creating /a), an out-of-bounds read can occur in audit_compare_dname_path(). The helper parent_len() returns 1 for "/". In audit_compare_dname_path(), when parentlen equals the full path length (1), the code sets p = path + 1 and pathlen = 1 - 1 = 0. The subsequent loop then dereferences p[pathlen - 1] (i.e., p[-1]), causing an out-of-bounds read. Fix this by adding a pathlen > 0 check to the while loop condition to prevent the out-of-bounds access. [PM: subject tweak, sign-off email fixes]

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/9735a9dcc307427e7d6336c54171682f1bac9789
• https://git.kernel.org/stable/c/4540f1d23e7f387880ce46d11b5cd3f27248bf8d