From: Jeff Xu jeffxu@google.com
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_=gZU6WEy5a...
History: V2: fix build error when CONFIG_SYSCTL is not defined.
V1: initial version https://lore.kernel.org/linux-mm/20230630031721.623955-3-jeffxu@google.com/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(-)
From: Jeff Xu jeffxu@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"
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_=gZU6WEy5a... 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 --- 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)
From: Jeff Xu jeffxu@google.com
Add selftest for sysctl vm.memfd_noexec is 2 (MEMFD_NOEXEC_SCOPE_NOEXEC_ENFORCED)
memfd_create(.., MFD_EXEC) should fail in this case.
Reported-by: Dominique Martinet asmadeus@codewreck.org Closes: https://lore.kernel.org/linux-mm/CABi2SkXUX_QqTQ10Yx9bBUGpN1wByOi_=gZU6WEy5a... Signed-off-by: Jeff Xu jeffxu@google.com --- tools/testing/selftests/memfd/memfd_test.c | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/tools/testing/selftests/memfd/memfd_test.c b/tools/testing/selftests/memfd/memfd_test.c index dba0e8ba002f..dbdd9ec5e397 100644 --- a/tools/testing/selftests/memfd/memfd_test.c +++ b/tools/testing/selftests/memfd/memfd_test.c @@ -1147,6 +1147,11 @@ static void test_sysctl_child(void) sysctl_assert_write("2"); mfd_fail_new("kern_memfd_sysctl_2", MFD_CLOEXEC | MFD_ALLOW_SEALING); + mfd_fail_new("kern_memfd_sysctl_2_MFD_EXEC", + MFD_CLOEXEC | MFD_EXEC); + fd = mfd_assert_new("", 0, MFD_NOEXEC_SEAL); + close(fd); + sysctl_fail_write("0"); sysctl_fail_write("1"); }
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