On 3/10/2021 10:17 AM, Mickaël Salaün wrote: > On 10/03/2021 18:22, Casey Schaufler wrote: >> On 3/10/2021 8:09 AM, Mickaël Salaün wrote: >>> Hi, >>> >>> The chroot system call is currently limited to be used by processes with >>> the CAP_SYS_CHROOT capability. This protects against malicious >>> procesess willing to trick SUID-like binaries. The following patch >>> allows unprivileged users to safely use chroot(2). >> Mount namespaces have pretty well obsoleted chroot(). CAP_SYS_CHROOT is >> one of the few fine grained capabilities. We're still finding edge cases >> (e.g. ptrace) where no_new_privs is imperfect. I doesn't seem that there >> is a compelling reason to remove the privilege requirement on chroot(). > What is the link between chroot and ptrace? The possibility of sophisticated interactions with no_new_privs. > What is interesting with CAP_SYS_CHROOT? CAP_SYS_CHROOT is specific to chroot. It doesn't give you privilege beyond what you expect, unlike CAP_CHOWN or CAP_SYS_ADMIN. Making chroot unprivileged is silly when it's possibly the best example of how the capability mechanism is supposed to work. > >>> This patch is a follow-up of a previous one sent by Andy Lutomirski some >>> time ago: >>> https://lore.kernel.org/lkml/0e2f0f54e19bff53a3739ecfddb4ffa9a6dbde4d.1327858005.git.luto@xxxxxxxxxxxxxx/ >>> >>> This patch can be applied on top of v5.12-rc2 . I would really >>> appreciate constructive reviews. >>> >>> Regards, >>> >>> Mickaël Salaün (1): >>> fs: Allow no_new_privs tasks to call chroot(2) >>> >>> fs/open.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++++++++--- >>> 1 file changed, 61 insertions(+), 3 deletions(-) >>> >>> >>> base-commit: a38fd8748464831584a19438cbb3082b5a2dab15
