int sd_memfd_new_from_fd(sd_memfd **m, int fd) {
sd_memfd *n;
+ int r;
assert_return(m, -EINVAL);
assert_return(fd >= 0, -EINVAL);
- /* Check if this is a sealable fd */
- if (fcntl(fd, F_GET_SEALS) < 0)
+ /* Check if this is a sealable fd. The kernel sets F_SEAL_SEAL on memfds
+ * that don't support sealing, so check for that, too. A file with
+ * *only* F_SEAL_SEAL set is the same as a random shmem file, so no
+ * reason to allow opening it as memfd. */
+ r = fcntl(fd, F_GET_SEALS);
+ if (r < 0 || r == F_SEAL_SEAL)
return -ENOTTY;
n = new0(struct sd_memfd, 1);
if (sealed < 0)
return sealed;
- q = mmap(NULL, size, sealed ? PROT_READ : PROT_READ|PROT_WRITE, MAP_PRIVATE, m->fd, offset);
+ if (sealed)
+ q = mmap(NULL, size, PROT_READ, MAP_PRIVATE, m->fd, offset);
+ else
+ q = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, m->fd, offset);
+
if (q == MAP_FAILED)
return -errno;