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dissect: make --detach work when passed the backing block device of a loopback device

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When systemd-loop@.service is instantiated for a block device (e.g. a
CD-ROM drive, which is the primary usecase now that --relax is used),
%f resolves to the backing block device rather than to the loopback
block device that was attached on top of it. In that case ExecStop=
hence invoked --detach on a block device that is not a loopback device
at all, which made loop_device_set_autoclear() a silent no-op, leaking
the attachment.

Hence, if --detach is passed a block device that is not a loopback
block device itself, search for the loopback block device backed by it,
the same way we already do for regular files. The kernel reports the
backing inode for block device nodes too, so the same inode matching
logic applies.
This commit is contained in:
Lennart Poettering
2026-09-22 16:04:26 +02:00
committed by Luca Boccassi
parent 6a16394cd6
commit b8ee13613c
1 changed files with 16 additions and 2 deletions
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src/dissect/dissect.c
+16 -2
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@@ -1855,10 +1855,24 @@ static int action_detach(const char *path) {
if (r < 0)
return log_error_errno(r, "Failed to open '%s' as loopback block device: %m", path);
} else if (S_ISREG(st.st_mode)) {
/* If the specified block device is not a loopback block device itself, it might be the
* backing device of one (this is the case when systemd-loop@.service is instantiated for a
* block device, e.g. a CD-ROM drive, in which case it is passed the backing device on
* ExecStop= too). Hence, in that case search for the loopback block device backed by it
* below, the same way as we do for regular files. */
if (LOOP_DEVICE_IS_FOREIGN(loop))
loop = loop_device_unref(loop);
} else if (!S_ISREG(st.st_mode))
return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "'%s' is neither a block device nor a regular file, refusing.", path);
if (!loop) {
_cleanup_(sd_device_enumerator_unrefp) sd_device_enumerator *e = NULL;
/* If a regular file is specified, search for a loopback block device that is backed by it */
/* If a regular file (or a block device that is not a loopback block device) is specified,
* search for a loopback block device that is backed by it. Note that the kernel reports
* the backing inode of a loopback device both for regular files and for block device
* nodes, hence we can match by inode in both cases. */
r = sd_device_enumerator_new(&e);
if (r < 0)