Messages in this thread | | | Date | Thu, 6 Jul 2017 07:47:31 +0200 | From | Willy Tarreau <> | Subject | Re: [RFC][PATCH] exec: Use init rlimits for setuid exec |
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On Wed, Jul 05, 2017 at 09:32:35PM -0700, Kees Cook wrote: > In an attempt to provide sensible rlimit defaults for setuid execs, this > inherits the namespace's init rlimits: > > $ ulimit -s > 8192 > $ ulimit -s unlimited > $ /bin/sh -c 'ulimit -s' > unlimited > $ sudo /bin/sh -c 'ulimit -s' > 8192 > > This is modified from Brad Spengler/PaX Team's hard-coded setuid exec > stack rlimit (8MB) in the last public patch of grsecurity/PaX based on > my understanding of the code. Changes or omissions from the original > code are mine and don't reflect the original grsecurity/PaX code. > > Signed-off-by: Kees Cook <keescook@chromium.org> > --- > Instead of copying all rlimits, we could also pick specific ones to copy > (e.g. RLIMIT_STACK, or ones from Andy's list) or exclude from copying > (probably better to blacklist than whitelist). > > I think this is the right way to find the ns init task, but maybe it > needs locking? > --- > fs/exec.c | 34 ++++++++++++++++++++++++++++++---- > 1 file changed, 30 insertions(+), 4 deletions(-) > > diff --git a/fs/exec.c b/fs/exec.c > index 904199086490..80e8b2bd4284 100644 > --- a/fs/exec.c > +++ b/fs/exec.c > @@ -1675,6 +1675,12 @@ static int exec_binprm(struct linux_binprm *bprm) > return ret; > } > > +static inline bool is_setuid_exec(struct linux_binprm *bprm) > +{ > + return (!uid_eq(bprm->cred->euid, current_euid()) || > + !gid_eq(bprm->cred->egid, current_egid())); > +} > + > /* > * sys_execve() executes a new program. > */ > @@ -1687,6 +1693,7 @@ static int do_execveat_common(int fd, struct filename *filename, > struct linux_binprm *bprm; > struct file *file; > struct files_struct *displaced; > + struct rlimit saved_rlim[RLIM_NLIMITS]; > int retval; > > if (IS_ERR(filename)) > @@ -1771,24 +1778,38 @@ static int do_execveat_common(int fd, struct filename *filename, > if (retval < 0) > goto out; > > + /* > + * From here forward, we've got credentials set up and we're > + * using resources, so do rlimit replacement before we start > + * copying strings. (Note that the RLIMIT_NPROC check has > + * already happened.) > + */ > + BUILD_BUG_ON(sizeof(saved_rlim) != sizeof(current->signal->rlim)); > + if (is_setuid_exec(bprm)) { > + memcpy(saved_rlim, current->signal->rlim, sizeof(saved_rlim)); > + memcpy(current->signal->rlim, > + task_active_pid_ns(current)->child_reaper->signal->rlim, > + sizeof(current->signal->rlim)); > + } > +
But you're not replacing just RLIMIT_STACK but all rlimits here. Please don't do this, as I mentionned elsewhere in the thread it will really become a pain at least for RLIMIT_CORE and RLIMIT_NOFILE. Better only apply RLIMIT_STACK as the commit message mentions it.
Willy
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