map_write() silently truncates uid_map/gid_map/projid_map values above U32_MAX modulo 2^32 on 64-bit kernels, so e.g. "4294967301 1000 1" is installed as "5 1000 1" without an error. Patch 1 rejects such values with -EINVAL. Patch 2 adds a selftest for all three fields and for the unchanged in-range path.
This is hardening, not a security fix. The patch and the selftest were drafted by Claude Code (Claude Opus 5.5) in an interactive session; I reviewed, built and tested them. The assistant flagged the truncation while reading map_write(), and I confirmed it by writing to uid_map on a running kernel. Tested on v7.3-rc4-393-g165768bb7026 under virtme-ng, x86_64 defconfig with CONFIG_USER_NS: all five selftest cases pass on the patched kernel. On an unpatched 6.8 host, four of the five fail as expected. Natasha Klaus (2): userns: reject uid_map/gid_map values that do not fit in u32 selftests/namespaces: add uid_map/gid_map range tests kernel/user_namespace.c | 14 +- tools/testing/selftests/namespaces/.gitignore | 1 + tools/testing/selftests/namespaces/Makefile | 3 +- .../selftests/namespaces/uid_map_range_test.c | 155 ++++++++++++++++++ 4 files changed, 169 insertions(+), 4 deletions(-) create mode 100644 tools/testing/selftests/namespaces/uid_map_range_test.c base-commit: 165768bb70265b5c38cf0b73fafd75be235f8b14 -- 2.34.1
