repart: when keeping ref to backing inode/devnode, use fd_reopen() rathern than F_DUPFD

Via the "backing_fd" variable we intend to pin the backing inode through
our entire code. So far we typically created the fd via F_DUPFD_CLOEXEC,
and thus any BSD lock taken one the original fd is shared with our
backing_fd reference. And if the origina fd is closed but our backing_fd
is not, we'll keep the BSD lock open, even if we then reopen the block
device through the backing_fd. If hit, this results in a deadlock.

Let's fix that by creating the backing_fd via fd_reopen(), so that the
locks are no longer shared, and if the original fd is closed all BSD
locks on it that are in effect are auto-released.

(Note the deadlock is only triggered if multiple operations on the same
backing inode are executed, i.e. factory reset, resize and applying of
partitions.)

Replaces: #24181

diff --git a/src/partition/repart.c b/src/partition/repart.c
index 8044b2eef7eb17ce346c1bda192b0bbd1f8eadd7..893431da2a9c1a9a7af7debb7e74b6ed0a0fbcae 100644 (file)
--- a/src/partition/repart.c
+++ b/src/partition/repart.c
@@ -1612,9 +1612,9 @@ static int context_load_partition_table(
 
         if (*backing_fd < 0) {
                 /* If we have no fd referencing the device yet, make a copy of the fd now, so that we have one */
-                *backing_fd = fcntl(fdisk_get_devfd(c), F_DUPFD_CLOEXEC, 3);
+                *backing_fd = fd_reopen(fdisk_get_devfd(c), O_RDONLY|O_CLOEXEC);
                 if (*backing_fd < 0)
-                        return log_error_errno(errno, "Failed to duplicate fdisk fd: %m");
+                        return log_error_errno(*backing_fd, "Failed to duplicate fdisk fd: %m");
         }
 
         /* Tell udev not to interfere while we are processing the device */