2023-07-05 06:41:54

by Jeff Xu

Subject: [PATCH v2 0/2] mm/memfd: fix sysctl MEMFD_NOEXEC_SCOPE_NOEXEC_ENFORCED

From: Jeff Xu <[email protected]>

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 <[email protected]> who reported the bug.
see [1] for context.

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

History:
V2: fix build error when CONFIG_SYSCTL is not defined.

V1: initial version
https://lore.kernel.org/linux-mm/[email protected]/T/

Jeff Xu (2):
mm/memfd: sysctl: fix MEMFD_NOEXEC_SCOPE_NOEXEC_ENFORCED
selftests/memfd: sysctl: fix MEMFD_NOEXEC_SCOPE_NOEXEC_ENFORCED

mm/memfd.c | 57 +++++++++++++---------
tools/testing/selftests/memfd/memfd_test.c | 5 ++
2 files changed, 38 insertions(+), 24 deletions(-)

--
2.41.0.255.g8b1d071c50-goog

2023-07-05 06:49:55

by Jeff Xu

Subject: [PATCH v2 1/2] mm/memfd: sysctl: fix MEMFD_NOEXEC_SCOPE_NOEXEC_ENFORCED

From: Jeff Xu <[email protected]>

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"

Fixes: 105ff5339f49 ("mm/memfd: add MFD_NOEXEC_SEAL and MFD_EXEC")
Reported-by: Dominique Martinet <[email protected]>
Closes: https://lore.kernel.org/linux-mm/CABi2SkXUX_QqTQ10Yx9bBUGpN1wByOi_=gZU6WEy5a8MaQY3Jw@mail.gmail.com/T/
Reported-by: kernel test robot <[email protected]>
Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
Signed-off-by: Jeff Xu <[email protected]>
---
mm/memfd.c | 57 +++++++++++++++++++++++++++++++-----------------------
1 file changed, 33 insertions(+), 24 deletions(-)

diff --git a/mm/memfd.c b/mm/memfd.c
index e763e76f1106..0bdbd2335af7 100644
--- 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)
--
2.41.0.255.g8b1d071c50-goog