mm/memfd: sysctl: fix MEMFD_NOEXEC_SCOPE_NOEXEC_ENFORCED

Patch series "mm/memfd: fix sysctl MEMFD_NOEXEC_SCOPE_NOEXEC_ENFORCED", v2.

When sysctl 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"

Thanks to Dominique Martinet <asmadeus@codewreck.org> who reported the bug.
see [1] for context.

[1] https://lore.kernel.org/linux-mm/CABi2SkXUX_QqTQ10Yx9bBUGpN1wByOi_=gZU6WEy5a8MaQY3Jw@mail.gmail.com/T/

This patch (of 2):

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://lkml.kernel.org/r/20230705063315.3680666-1-jeffxu@google.com
Link: https://lkml.kernel.org/r/20230705063315.3680666-2-jeffxu@google.com
Fixes: 105ff5339f49 ("mm/memfd: add MFD_NOEXEC_SEAL and MFD_EXEC")
Reported-by: Dominique Martinet <asmadeus@codewreck.org>
Closes: https://lore.kernel.org/linux-mm/CABi2SkXUX_QqTQ10Yx9bBUGpN1wByOi_=gZU6WEy5a8MaQY3Jw@mail.gmail.com/T/
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202306301351.kkbSegQW-lkp@intel.com/
Signed-off-by: Jeff Xu <jeffxu@google.com>
Cc: Daniel Verkamp <dverkamp@chromium.org>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jorge Lucangeli Obes <jorgelo@chromium.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/memfd.c b/mm/memfd.c
index e763e76f11064586faad35bb3d2831c6ddda23cf..0bdbd2335af751b3c85a97251daccaecbd86a9c3 100644 (file)
--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -268,6 +268,36 @@ 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 check_sysctl_memfd_noexec(unsigned int *flags)
+{
+#ifdef CONFIG_SYSCTL
+       char comm[TASK_COMM_LEN];
+       int sysctl = MEMFD_NOEXEC_SCOPE_EXEC;
+       struct pid_namespace *ns;
+
+       ns = task_active_pid_ns(current);
+       if (ns)
+               sysctl = ns->memfd_noexec_scope;
+
+       if (!(*flags & (MFD_EXEC | MFD_NOEXEC_SEAL))) {
+               if (sysctl == MEMFD_NOEXEC_SCOPE_NOEXEC_SEAL)
+                       *flags |= MFD_NOEXEC_SEAL;
+               else
+                       *flags |= MFD_EXEC;
+       }
+
+       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;
+       }
+#endif
+
+       return 0;
+}
+
 SYSCALL_DEFINE2(memfd_create,
                const char __user *, uname,
                unsigned int, flags)
@@ -294,35 +324,14 @@ 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:
-                       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
                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 (check_sysctl_memfd_noexec(&flags) < 0)
+               return -EACCES;
+
        /* length includes terminating zero */
        len = strnlen_user(uname, MFD_NAME_MAX_LEN + 1);
        if (len <= 0)