[PATCH] kernel: reduce required permission for prctl_set_mm

[Andrey Vagin <avagin@openvz.org>]

Currently prctl_set_mm requires the global CAP_SYS_RESOURCE,
this patch reduce requiremence to CAP_SYS_RESOURCE in the current
namespace.

When we restore a task we need to set up text, data and data heap sizes
from userspace to the values a task had at checkpoint time.

Currently we can not restore these parameters, if a task lives in
a non-root user name space, because it has no capabilities in the
parent namespace.

prctl_set_mm() changes parameters of the current task and doesn't affect
other tasks.

This patch affects the RLIMIT_DATA limit, because a consumtiuon is
calculated relatively to mm->end_data, mm->start_data, mm->start_brk.

rlim = rlimit(RLIMIT_DATA);
if (rlim < RLIM_INFINITY && (brk - mm->start_brk) +
		(mm->end_data - mm->start_data) > rlim)
	goto out;

This limit affects calls to brk() and sbrk(), but it doesn't affect
mmap. So I think requirement of CAP_SYS_RESOURCE in the current
namespace is enough for this limit.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Robin Holt <holt@sgi.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Kees Cook <keescook@chromium.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Chen Gang <gang.chen@asianux.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Aditya Kali <adityakali@google.com>
Cc: security@kernel.org
Signed-off-by: Andrey Vagin <avagin@openvz.org>
---
 kernel/sys.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sys.c b/kernel/sys.c
index c0a58be..6f36fb3 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1701,7 +1701,7 @@ static int prctl_set_mm(int opt, unsigned long addr,
 	if (arg5 || (arg4 && opt != PR_SET_MM_AUXV))
 		return -EINVAL;
 
-	if (!capable(CAP_SYS_RESOURCE))
+	if (!ns_capable(current_user_ns(), CAP_SYS_RESOURCE))
 		return -EPERM;
 
 	if (opt == PR_SET_MM_EXE_FILE)
-- 
1.8.5.3