When refreshing after a reboot, force lock allocation

After a reboot, when we refresh Podman's state, we retrieved the
lock from the fresh SHM instance, but we did not mark it as
allocated to prevent it being handed out to other containers and
pods.

Provide a method for marking locks as in-use, and use it when we
refresh Podman state after a reboot.

Fixes #2900

Signed-off-by: Matthew Heon <matthew.heon@pm.me>

3 files changed, 73 insertions, 0 deletions

diff --git a/libpod/lock/shm/shm_lock.c b/libpod/lock/shm/shm_lock.c
index d11fce71a..047d3c417 100644
--- a/libpod/lock/shm/shm_lock.c
+++ b/libpod/lock/shm/shm_lock.c
@@ -354,6 +354,61 @@ int64_t allocate_semaphore(shm_struct_t *shm) {
   return -1 * ENOSPC;
 }
 
+// Allocate the semaphore with the given ID.
+// Returns an error if the semaphore with this ID does not exist, or has already
+// been allocated.
+// Returns 0 on success, or negative errno values on failure.
+int32_t allocate_given_semaphore(shm_struct_t *shm, uint32_t sem_index) {
+  int bitmap_index, index_in_bitmap, ret_code;
+  bitmap_t test_map;
+
+  if (shm == NULL) {
+    return -1 * EINVAL;
+  }
+
+  // Check if the lock index is valid
+  if (sem_index >= shm->num_locks) {
+    return -1 * EINVAL;
+  }
+
+  bitmap_index = sem_index / BITMAP_SIZE;
+  index_in_bitmap = sem_index % BITMAP_SIZE;
+
+  // This should never happen if the sem_index test above succeeded, but better
+  // safe than sorry
+  if (bitmap_index >= shm->num_bitmaps) {
+    return -1 * EFAULT;
+  }
+
+  test_map = 0x1 << index_in_bitmap;
+
+  // Lock the mutex controlling access to our shared memory
+  ret_code = take_mutex(&(shm->segment_lock));
+  if (ret_code != 0) {
+    return -1 * ret_code;
+  }
+
+  // Check if the semaphore is allocated
+  if ((test_map & shm->locks[bitmap_index].bitmap) != 0) {
+    ret_code = release_mutex(&(shm->segment_lock));
+    if (ret_code != 0) {
+      return -1 * ret_code;
+    }
+
+    return -1 * EEXIST;
+  }
+
+  // The semaphore is not allocated, allocate it
+  shm->locks[bitmap_index].bitmap = shm->locks[bitmap_index].bitmap | test_map;
+
+  ret_code = release_mutex(&(shm->segment_lock));
+  if (ret_code != 0) {
+    return -1 * ret_code;
+  }
+
+  return 0;
+}
+
 // Deallocate a given semaphore
 // Returns 0 on success, negative ERRNO values on failure
 int32_t deallocate_semaphore(shm_struct_t *shm, uint32_t sem_index) {
diff --git a/libpod/lock/shm/shm_lock.go b/libpod/lock/shm/shm_lock.go
index e70ea8743..c21e9a221 100644
--- a/libpod/lock/shm/shm_lock.go
+++ b/libpod/lock/shm/shm_lock.go
@@ -134,6 +134,23 @@ func (locks *SHMLocks) AllocateSemaphore() (uint32, error) {
 	return uint32(retCode), nil
 }
 
+// AllocateGivenSemaphore allocates the given semaphore from the shared-memory
+// segment for use by a container or pod.
+// If the semaphore is already in use or the index is invalid an error will be
+// returned.
+func (locks *SHMLocks) AllocateGivenSemaphore(sem uint32) error {
+	if !locks.valid {
+		return errors.Wrapf(syscall.EINVAL, "locks have already been closed")
+	}
+
+	retCode := C.allocate_given_semaphore(locks.lockStruct, C.uint32_t(sem))
+	if retCode < 0 {
+		return syscall.Errno(-1 * retCode)
+	}
+
+	return nil
+}
+
 // DeallocateSemaphore frees a semaphore in a shared-memory segment so it can be
 // reallocated to another container or pod.
 // The given semaphore must be already allocated, or an error will be returned.
diff --git a/libpod/lock/shm/shm_lock.h b/libpod/lock/shm/shm_lock.h
index 58e4297e2..759f8178a 100644
--- a/libpod/lock/shm/shm_lock.h
+++ b/libpod/lock/shm/shm_lock.h
@@ -39,6 +39,7 @@ shm_struct_t *setup_lock_shm(char *path, uint32_t num_locks, int *error_code);
 shm_struct_t *open_lock_shm(char *path, uint32_t num_locks, int *error_code);
 int32_t close_lock_shm(shm_struct_t *shm);
 int64_t allocate_semaphore(shm_struct_t *shm);
+int32_t allocate_given_semaphore(shm_struct_t *shm, uint32_t sem_index);
 int32_t deallocate_semaphore(shm_struct_t *shm, uint32_t sem_index);
 int32_t deallocate_all_semaphores(shm_struct_t *shm);
 int32_t lock_semaphore(shm_struct_t *shm, uint32_t sem_index);