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Date: Fri, 4 Jul 2014 00:34:28 +0400
From: Cyrill Gorcunov <gorcunov@...il.com>
To: linux-kernel@...r.kernel.org
Cc: Kees Cook <keescook@...omium.org>, Tejun Heo <tj@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Andrew Vagin <avagin@...nvz.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Serge Hallyn <serge.hallyn@...onical.com>,
Pavel Emelyanov <xemul@...allels.com>,
Vasiliy Kulikov <segoon@...nwall.com>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
Michael Kerrisk <mtk.manpages@...il.com>
Subject: [RFC 2/2] prctl: PR_SET_MM -- Introduce PR_SET_MM_MAP operation
On Thu, Jul 03, 2014 at 06:33:20PM +0400, Cyrill Gorcunov wrote:
> During development of c/r we've noticed that in case if we need to
> support user namespaces we face a problem with capabilities in
> prctl(PR_SET_MM, ...) call.
Sigh, I updated changelog after I started writting the 0/0 message,
here is an updated variant (only patch description is changed code
remains the same). Sorry for inconvenience.
---
From: Cyrill Gorcunov <gorcunov@...nvz.org>
Subject: [RFC 2/2] prctl: PR_SET_MM -- Introduce PR_SET_MM_MAP operation
During development of c/r we've noticed that in case if we need to
support user namespaces we face a problem with capabilities in
prctl(PR_SET_MM, ...) call.
Current PR_SET_MM code forbids to modify fields if no CAP_SYS_RESOURCE
granted, but rather relies on one who use this interface is passing
more-less sane values (though the values must pass the basic validation
procedure).
It seems a better approach is to eliminate CAP_SYS_RESOURCE check but
provide all new values in one bundle, which would allow the kernel to make
more intensive test for sanity of values and same time allow us to
support checkpoint/restore of user namespaces.
Thus a new command (PR_SET_MM_MAP) introduced. It takes a pointer of
prctl_mm_map structure which carries all members to be updated.
Most intensive work is done in validate_prctl_map_locked helper,
because we need to make sure the values are valid. Thus we do
- check the values are laying inside available user address space
- stack, brk, command line arguments and evnironment variables
must point to already existing VMA
- values must be ordered (start < end)
- if RLIMITs are defined don't allow to exceed it with new values
Since it uses prctl_set_mm_exe_file_locked helper, updating the
exe-file link remains one-shot action.
Still note that updating exe-file link now doesn't require
sys-resource capability anymore, after all there is no much
profit in preventing setup own file link (there are a number
of ways to execute own code -- ptrace, ld-preload, so that
the only reliable way to find which exactly code is executed
is to inspect running program memory).
I believe the old interface should be deprecated and ripped off
in a couple of kernel releases if noone against.
To test if new interface is implemented in the kernel one
can pass PR_SET_MM_MAP_SIZE opcode and the kernel returns
the size of currently supported struct prctl_mm_map.
Signed-off-by: Cyrill Gorcunov <gorcunov@...nvz.org>
Cc: Kees Cook <keescook@...omium.org>
Cc: Tejun Heo <tj@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Andrew Vagin <avagin@...nvz.org>
Cc: Eric W. Biederman <ebiederm@...ssion.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Serge Hallyn <serge.hallyn@...onical.com>
Cc: Pavel Emelyanov <xemul@...allels.com>
Cc: Vasiliy Kulikov <segoon@...nwall.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: Michael Kerrisk <mtk.manpages@...il.com>
---
include/uapi/linux/prctl.h | 19 ++++
kernel/sys.c | 188 ++++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 206 insertions(+), 1 deletion(-)
Index: linux-2.6.git/include/uapi/linux/prctl.h
===================================================================
--- linux-2.6.git.orig/include/uapi/linux/prctl.h
+++ linux-2.6.git/include/uapi/linux/prctl.h
@@ -119,6 +119,25 @@
# define PR_SET_MM_ENV_END 11
# define PR_SET_MM_AUXV 12
# define PR_SET_MM_EXE_FILE 13
+# define PR_SET_MM_MAP 14
+# define PR_SET_MM_MAP_SIZE 15
+
+struct prctl_mm_map {
+ unsigned long start_code;
+ unsigned long end_code;
+ unsigned long start_data;
+ unsigned long end_data;
+ unsigned long start_brk;
+ unsigned long brk;
+ unsigned long start_stack;
+ unsigned long arg_start;
+ unsigned long arg_end;
+ unsigned long env_start;
+ unsigned long env_end;
+ unsigned long *auxv;
+ unsigned int auxv_size;
+ int exe_fd;
+};
/*
* Set specific pid that is allowed to ptrace the current task.
Index: linux-2.6.git/kernel/sys.c
===================================================================
--- linux-2.6.git.orig/kernel/sys.c
+++ linux-2.6.git/kernel/sys.c
@@ -1687,6 +1687,187 @@ exit:
return err;
}
+/*
+ * WARNING: we don't require any capability here so be very careful
+ * in what is allowed for modification from userspace.
+ */
+static int validate_prctl_map_locked(struct prctl_mm_map *prctl_map)
+{
+ unsigned long mmap_max_addr = TASK_SIZE;
+ struct mm_struct *mm = current->mm;
+ struct vm_area_struct *stack_vma;
+ unsigned long rlim;
+ int error = 0;
+
+ /*
+ * Make sure the members are not somewhere outside
+ * of allowed address space.
+ */
+#define __prctl_check_addr_space(__map, __member) \
+ ({ \
+ int __rc; \
+ if ((unsigned long)__map->__member < mmap_max_addr && \
+ (unsigned long)__map->__member >= mmap_min_addr) \
+ __rc = 0; \
+ else \
+ __rc = -EINVAL; \
+ __rc; \
+ })
+
+ error |= __prctl_check_addr_space(prctl_map, start_code);
+ error |= __prctl_check_addr_space(prctl_map, end_code);
+ error |= __prctl_check_addr_space(prctl_map, start_data);
+ error |= __prctl_check_addr_space(prctl_map, end_data);
+ error |= __prctl_check_addr_space(prctl_map, start_stack);
+ error |= __prctl_check_addr_space(prctl_map, start_brk);
+ error |= __prctl_check_addr_space(prctl_map, brk);
+ error |= __prctl_check_addr_space(prctl_map, arg_start);
+ error |= __prctl_check_addr_space(prctl_map, arg_end);
+ error |= __prctl_check_addr_space(prctl_map, env_start);
+ error |= __prctl_check_addr_space(prctl_map, env_end);
+ if (error)
+ goto out;
+#undef __prctl_check_addr_space
+
+ /*
+ * Stack, brk, command line arguments and environment must exist.
+ */
+ stack_vma = find_vma(mm, prctl_map->start_stack);
+ if (!stack_vma) {
+ error = -EINVAL;
+ goto out;
+ }
+#define __prctl_check_vma(mm, addr) find_vma(mm, addr) ? 0 : -EINVAL
+ error |= __prctl_check_vma(mm, prctl_map->start_brk);
+ error |= __prctl_check_vma(mm, prctl_map->brk);
+ error |= __prctl_check_vma(mm, prctl_map->arg_start);
+ error |= __prctl_check_vma(mm, prctl_map->arg_end);
+ error |= __prctl_check_vma(mm, prctl_map->env_start);
+ error |= __prctl_check_vma(mm, prctl_map->env_end);
+ if (error)
+ goto out;
+#undef __prctl_check_vma
+
+ /*
+ * Make sure the pairs are ordered.
+ */
+#define __prctl_check_order(__map, __m1, __m2) \
+ __map->__m2 <= __map->__m1
+ if (__prctl_check_order(prctl_map, start_code, end_code) ||
+ __prctl_check_order(prctl_map, start_data, end_data) ||
+ __prctl_check_order(prctl_map, arg_start, arg_end) ||
+ __prctl_check_order(prctl_map, env_start, env_end))
+ goto out;
+#undef __prctl_check_order
+
+ error = -EINVAL;
+
+ /*
+ * @brk should be after @end_data in traditional maps.
+ */
+ if (prctl_map->start_brk <= prctl_map->end_data ||
+ prctl_map->brk <= prctl_map->end_data)
+ goto out;
+
+ /*
+ * Neither we should allow to override limits if they set.
+ */
+ rlim = rlimit(RLIMIT_DATA);
+ if (rlim < RLIM_INFINITY) {
+ if ((prctl_map->brk - prctl_map->start_brk) +
+ (prctl_map->end_data - prctl_map->start_data) > rlim)
+ goto out;
+ }
+
+ rlim = rlimit(RLIMIT_STACK);
+ if (rlim < RLIM_INFINITY) {
+#ifdef CONFIG_STACK_GROWSUP
+ unsigned long left = stack_vma->vm_end - prctl_map->start_stack;
+#else
+ unsigned long left = prctl_map->start_stack - stack_vma->vm_start;
+#endif
+ if (left > rlim)
+ goto out;
+ }
+
+ /*
+ * Someone is trying to cheat the auxv vector.
+ */
+ if (prctl_map->auxv && prctl_map->auxv_size > sizeof(mm->saved_auxv))
+ goto out;
+ error = 0;
+out:
+ return error;
+}
+
+static int prctl_set_mm_map(int opt, const void __user *addr, unsigned long data_size)
+{
+ struct prctl_mm_map prctl_map = { .exe_fd = (u32)-1, };
+ unsigned long user_auxv[AT_VECTOR_SIZE];
+ struct mm_struct *mm = current->mm;
+ int error = -EINVAL;
+
+ BUILD_BUG_ON(sizeof(user_auxv) != sizeof(mm->saved_auxv));
+
+ if (opt == PR_SET_MM_MAP_SIZE)
+ return put_user((unsigned int)sizeof(prctl_map),
+ (unsigned int __user *)addr);
+
+ if (data_size != sizeof(prctl_map))
+ return -EINVAL;
+
+ if (copy_from_user(&prctl_map, addr, sizeof(prctl_map)))
+ return -EFAULT;
+
+ down_read(&mm->mmap_sem);
+
+ if (validate_prctl_map_locked(&prctl_map))
+ goto out;
+
+ if (prctl_map.auxv && prctl_map.auxv_size) {
+ up_read(&mm->mmap_sem);
+ memset(user_auxv, 0, sizeof(user_auxv));
+ error = copy_from_user(user_auxv,
+ (const void __user *)prctl_map.auxv,
+ prctl_map.auxv_size);
+ down_read(&mm->mmap_sem);
+ if (error)
+ goto out;
+ }
+
+ if (prctl_map.exe_fd != (u32)-1) {
+ error = prctl_set_mm_exe_file_locked(mm, prctl_map.exe_fd);
+ if (error)
+ goto out;
+ }
+
+ if (prctl_map.auxv && prctl_map.auxv_size) {
+ user_auxv[AT_VECTOR_SIZE - 2] = 0;
+ user_auxv[AT_VECTOR_SIZE - 1] = 0;
+
+ task_lock(current);
+ memcpy(mm->saved_auxv, user_auxv, sizeof(user_auxv));
+ task_unlock(current);
+ }
+
+ mm->start_code = prctl_map.start_code;
+ mm->end_code = prctl_map.end_code;
+ mm->start_data = prctl_map.start_data;
+ mm->end_data = prctl_map.end_data;
+ mm->start_brk = prctl_map.start_brk;
+ mm->brk = prctl_map.brk;
+ mm->start_stack = prctl_map.start_stack;
+ mm->arg_start = prctl_map.arg_start;
+ mm->arg_end = prctl_map.arg_end;
+ mm->env_start = prctl_map.env_start;
+ mm->env_end = prctl_map.env_end;
+
+ error = 0;
+out:
+ up_read(&mm->mmap_sem);
+ return error;
+}
+
static int prctl_set_mm(int opt, unsigned long addr,
unsigned long arg4, unsigned long arg5)
{
@@ -1695,9 +1876,14 @@ static int prctl_set_mm(int opt, unsigne
struct vm_area_struct *vma;
int error;
- if (arg5 || (arg4 && opt != PR_SET_MM_AUXV))
+ if (arg5 || (arg4 && (opt != PR_SET_MM_AUXV &&
+ opt != PR_SET_MM_MAP &&
+ opt != PR_SET_MM_MAP_SIZE)))
return -EINVAL;
+ if (opt == PR_SET_MM_MAP || opt == PR_SET_MM_MAP_SIZE)
+ return prctl_set_mm_map(opt, (const void __user *)addr, arg4);
+
if (!capable(CAP_SYS_RESOURCE))
return -EPERM;
--
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