[CRIU] [PATCH] report the potential selinux problem if mmap_seized() fails

[Oleg Nesterov]

selinux can deny mmap(PROT_WRITE | PROT_EXEC) and in this case it is
not clear why CRIU fails, "Can't allocate memory for parasite blob"
doesn't tell too much. Add a pr_warn() hint for the user.

Signed-off-by: Oleg Nesterov <oleg at redhat.com>
---
 arch/x86/crtools.c |   11 +++++++++--
 1 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/x86/crtools.c b/arch/x86/crtools.c
index 02ce2e5..06d824a 100644
--- a/arch/x86/crtools.c
+++ b/arch/x86/crtools.c
@@ -445,8 +445,15 @@ void *mmap_seized(struct parasite_ctl *ctl,
 
 	err = syscall_seized(ctl, __NR_mmap, &map,
 			(unsigned long)addr, length, prot, flags, fd, offset);
-	if (err < 0 || map > TASK_SIZE)
-		map = 0;
+	if (err < 0)
+		return NULL;
+
+	if (IS_ERR_VALUE(map)) {
+		if (map == -EACCES && (prot & PROT_WRITE) && (prot & PROT_EXEC))
+			pr_warn("mmap(PROT_WRITE | PROT_EXEC) failed for %d, "
+				"check selinux execmem policy\n", ctl->pid.real);
+		return NULL;
+	}
 
 	return (void *)map;
 }
-- 
1.5.5.1