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

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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
(cherry picked from commit 38f81e9374)
(cherry picked from commit d3e84e4703)
This commit is contained in:
Lennart Poettering 2022-08-02 18:16:21 +02:00 committed by Zbigniew Jędrzejewski-Szmek
parent a2fc30409d
commit 8e6ba03724
1 changed files with 2 additions and 2 deletions
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4
src/partition/repart.c
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@ -1593,9 +1593,9 @@ 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 */