[PATCH v2 12/16] device-mapper: inform caller about already-existing device

Demi Marie Obenour
2023-05-30T20:33:25Z

Not only is this helpful for debugging, it also saves the caller an
ioctl in the case where a device should be used if it exists or created
otherwise. To ensure existing userspace is not broken, this feature is
only enabled in strict mode.

Signed-off-by: Demi Marie Obenour <demi@invisiblethingslab.com>
---
drivers/md/dm-ioctl.c | 26 +++++++++++++++++++-------
1 file changed, 19 insertions(+), 7 deletions(-)

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index 17ece816d490b6c40d019da131ade44c9a201dab..44425093d3b908abf80e05e1fc99a26b17e18a42 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -256,11 +256,13 @@ static void free_cell(struct hash_cell *hc)
}
}

+static void __dev_status(struct mapped_device *md, struct dm_ioctl *param);
+
/*
* The kdev_t and uuid of a device can never change once it is
* initially inserted.
*/
-static int dm_hash_insert(const char *name, const char *uuid, struct mapped_device *md)
+static int dm_hash_insert(const char *name, const char *uuid, struct mapped_device *md, struct dm_ioctl *param)
{
struct hash_cell *cell, *hc;

@@ -277,6 +279,8 @@ static int dm_hash_insert(const char *name, const char *uuid, struct mapped_devi
down_write(&_hash_lock);
hc = __get_name_cell(name);
if (hc) {
+ if (param)
+ __dev_status(hc->md, param);
dm_put(hc->md);
goto bad;
}
@@ -287,6 +291,8 @@ static int dm_hash_insert(const char *name, const char *uuid, struct mapped_devi
hc = __get_uuid_cell(uuid);
if (hc) {
__unlink_name(cell);
+ if (param)
+ __dev_status(hc->md, param);
dm_put(hc->md);
goto bad;
}
@@ -901,12 +907,14 @@ static int dev_create(struct file *filp, struct dm_ioctl *param, size_t param_si
m = MINOR(huge_decode_dev(param->dev));

r = dm_create(m, &md, param->flags & DM_DISABLE_UEVENTS_FLAG);
- if (r)
+ if (r) {
+ DMERR("Could not create device-mapper device");
return r;
+ }

param->flags &= ~DM_INACTIVE_PRESENT_FLAG;

- r = dm_hash_insert(param->name, *param->uuid ? param->uuid : NULL, md);
+ r = dm_hash_insert(param->name, *param->uuid ? param->uuid : NULL, md, param);
if (r) {
dm_put(md);
dm_destroy(md);
@@ -2269,7 +2277,6 @@ static int ctl_ioctl(struct file *file, uint command, struct dm_ioctl __user *us
goto out;
/* This XOR keeps only the flags validate_params has changed. */
old_flags ^= param->flags;
-
param->data_size = sloppy_checks(param) ? offsetof(struct dm_ioctl, data) : sizeof(struct dm_ioctl);
r = fn(file, param, input_param_size);

@@ -2284,9 +2291,14 @@ static int ctl_ioctl(struct file *file, uint command, struct dm_ioctl __user *us
param->flags |= old_flags;

/*
- * Copy the results back to userland.
+ * Copy the results back to userland if either:
+ *
+ * - The ioctl succeeded.
+ * - The ioctl is DM_DEV_CREATE, the return value is -EBUSY,
+ * and strict parameter checking is enabled.
*/
- if (!r && copy_to_user(user, param, param->data_size))
+ if ((!r || (!sloppy_checks(param) && cmd == DM_DEV_CREATE_CMD && r == -EBUSY)) &&
+ copy_to_user(user, param, param->data_size))
r = -EFAULT;

out:
@@ -2465,7 +2477,7 @@ int __init dm_early_create(struct dm_ioctl *dmi,
return r;

/* hash insert */
- r = dm_hash_insert(dmi->name, *dmi->uuid ? dmi->uuid : NULL, md);
+ r = dm_hash_insert(dmi->name, *dmi->uuid ? dmi->uuid : NULL, md, NULL);
if (r)
goto err_destroy_dm;