[PATCH v1 1/2] mm/memfd: sysctl: fix MEMFD_NOEXEC_SCOPE_NOEXEC_ENFORCED

[jeffxu at chromium.org]

From: Jeff Xu <jeffxu at google.com>

When vm.memfd_noexec is 2 (MEMFD_NOEXEC_SCOPE_NOEXEC_ENFORCED),
memfd_create(.., MFD_EXEC) should fail.

This complies with how MEMFD_NOEXEC_SCOPE_NOEXEC_ENFORCED is
defined - "memfd_create() without MFD_NOEXEC_SEAL will be rejected"

Link:https://lore.kernel.org/linux-mm/CABi2SkXUX_QqTQ10Yx9bBUGpN1wByOi_=gZU6WEy5a8MaQY3Jw@mail.gmail.com/T/
Fixes: 105ff5339f49 ("mm/memfd: add MFD_NOEXEC_SEAL and MFD_EXEC")
Reported-by: Dominique Martinet <asmadeus at codewreck.org>
Signed-off-by: Jeff Xu <jeffxu at google.com>
---
 mm/memfd.c | 48 +++++++++++++++++++++++++-----------------------
 1 file changed, 25 insertions(+), 23 deletions(-)

diff --git a/mm/memfd.c b/mm/memfd.c
index e763e76f1106..812750298e8a 100644
--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -268,6 +268,19 @@ long memfd_fcntl(struct file *file, unsigned int cmd, unsigned int arg)
 
 #define MFD_ALL_FLAGS (MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_HUGETLB | MFD_NOEXEC_SEAL | MFD_EXEC)
 
+static int sysctl_memfd_noexec(void)
+{
+	int sysctl = MEMFD_NOEXEC_SCOPE_EXEC;
+#ifdef CONFIG_SYSCTL
+	struct pid_namespace *ns;
+
+	ns = task_active_pid_ns(current);
+	if (ns)
+		sysctl = ns->memfd_noexec_scope;
+#endif
+	return sysctl;
+}
+
 SYSCALL_DEFINE2(memfd_create,
 		const char __user *, uname,
 		unsigned int, flags)
@@ -278,6 +291,7 @@ SYSCALL_DEFINE2(memfd_create,
 	int fd, error;
 	char *name;
 	long len;
+	int sysctl = sysctl_memfd_noexec();
 
 	if (!(flags & MFD_HUGETLB)) {
 		if (flags & ~(unsigned int)MFD_ALL_FLAGS)
@@ -294,35 +308,23 @@ SYSCALL_DEFINE2(memfd_create,
 		return -EINVAL;
 
 	if (!(flags & (MFD_EXEC | MFD_NOEXEC_SEAL))) {
-#ifdef CONFIG_SYSCTL
-		int sysctl = MEMFD_NOEXEC_SCOPE_EXEC;
-		struct pid_namespace *ns;
-
-		ns = task_active_pid_ns(current);
-		if (ns)
-			sysctl = ns->memfd_noexec_scope;
-
-		switch (sysctl) {
-		case MEMFD_NOEXEC_SCOPE_EXEC:
-			flags |= MFD_EXEC;
-			break;
-		case MEMFD_NOEXEC_SCOPE_NOEXEC_SEAL:
+		if (sysctl == MEMFD_NOEXEC_SCOPE_NOEXEC_SEAL)
 			flags |= MFD_NOEXEC_SEAL;
-			break;
-		default:
-			pr_warn_once(
-				"memfd_create(): MFD_NOEXEC_SEAL is enforced, pid=%d '%s'\n",
-				task_pid_nr(current), get_task_comm(comm, current));
-			return -EINVAL;
-		}
-#else
-		flags |= MFD_EXEC;
-#endif
+		else
+			flags |= MFD_EXEC;
+
 		pr_warn_once(
 			"memfd_create() without MFD_EXEC nor MFD_NOEXEC_SEAL, pid=%d '%s'\n",
 			task_pid_nr(current), get_task_comm(comm, current));
 	}
 
+	if (flags & MFD_EXEC && sysctl >= MEMFD_NOEXEC_SCOPE_NOEXEC_ENFORCED) {
+		pr_warn_once(
+			"memfd_create(): MFD_NOEXEC_SEAL is enforced, pid=%d '%s'\n",
+			task_pid_nr(current), get_task_comm(comm, current));
+		return -EACCES;
+	}
+
 	/* length includes terminating zero */
 	len = strnlen_user(uname, MFD_NAME_MAX_LEN + 1);
 	if (len <= 0)
-- 
2.41.0.255.g8b1d071c50-goog