Commit 69b736e7 authored by Kevin Wolf's avatar Kevin Wolf
Browse files

block: Make permission changes in reopen less wrong 



The way that reopen interacts with permission changes has one big
problem: Both operations are recursive, and the permissions are changes
for each node in the reopen queue.

For a simple graph that consists just of parent and child,
.bdrv_check_perm will be called twice for the child, once recursively
when adjusting the permissions of parent, and once again when the child
itself is reopened.

Even worse, the first .bdrv_check_perm call happens before
.bdrv_reopen_prepare was called for the child and the second one is
called afterwards.

Making sure that .bdrv_check_perm (and the other permission callbacks)
are called only once is hard. We can cope with multiple calls right now,
but as soon as file-posix gets a dynamic auto-read-only that may need to
open a new file descriptor, we get the additional requirement that all
of them are after the .bdrv_reopen_prepare call.

So reorder things in bdrv_reopen_multiple() to first call
.bdrv_reopen_prepare for all involved nodes and only then adjust
permissions.

Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
parent a4615ab3

block.c

+24 −11
Original line number Diff line number Diff line
@@ -1698,6 +1698,7 @@ static void bdrv_child_set_perm(BdrvChild *c, uint64_t perm, uint64_t shared); 


typedef struct BlockReopenQueueEntry {

     bool prepared;

     bool perms_checked;

     BDRVReopenState state;

     QSIMPLEQ_ENTRY(BlockReopenQueueEntry) entry;

} BlockReopenQueueEntry;
@@ -3166,6 +3167,16 @@ int bdrv_reopen_multiple(AioContext *ctx, BlockReopenQueue *bs_queue, Error **er 
        bs_entry->prepared = true;

    }



    QSIMPLEQ_FOREACH(bs_entry, bs_queue, entry) {

        BDRVReopenState *state = &bs_entry->state;

        ret = bdrv_check_perm(state->bs, bs_queue, state->perm,

                              state->shared_perm, NULL, errp);

        if (ret < 0) {

            goto cleanup_perm;

        }

        bs_entry->perms_checked = true;

    }



    /* If we reach this point, we have success and just need to apply the

     * changes

     */
@@ -3174,7 +3185,20 @@ int bdrv_reopen_multiple(AioContext *ctx, BlockReopenQueue *bs_queue, Error **er 
    }



    ret = 0;

cleanup_perm:

    QSIMPLEQ_FOREACH_SAFE(bs_entry, bs_queue, entry, next) {

        BDRVReopenState *state = &bs_entry->state;



        if (!bs_entry->perms_checked) {

            continue;

        }



        if (ret == 0) {

            bdrv_set_perm(state->bs, state->perm, state->shared_perm);

        } else {

            bdrv_abort_perm_update(state->bs);

        }

    }

cleanup:

    QSIMPLEQ_FOREACH_SAFE(bs_entry, bs_queue, entry, next) {

        if (ret) {
@@ -3428,12 +3452,6 @@ int bdrv_reopen_prepare(BDRVReopenState *reopen_state, BlockReopenQueue *queue, 
        } while ((entry = qdict_next(reopen_state->options, entry)));

    }



    ret = bdrv_check_perm(reopen_state->bs, queue, reopen_state->perm,

                          reopen_state->shared_perm, NULL, errp);

    if (ret < 0) {

        goto error;

    }



    ret = 0;



    /* Restore the original reopen_state->options QDict */
@@ -3500,9 +3518,6 @@ void bdrv_reopen_commit(BDRVReopenState *reopen_state) 


    bdrv_refresh_limits(bs, NULL);



    bdrv_set_perm(reopen_state->bs, reopen_state->perm,

                  reopen_state->shared_perm);



    new_can_write =

        !bdrv_is_read_only(bs) && !(bdrv_get_flags(bs) & BDRV_O_INACTIVE);

    if (!old_can_write && new_can_write && drv->bdrv_reopen_bitmaps_rw) {
@@ -3534,8 +3549,6 @@ void bdrv_reopen_abort(BDRVReopenState *reopen_state) 
    if (drv->bdrv_reopen_abort) {

        drv->bdrv_reopen_abort(reopen_state);

    }



    bdrv_abort_perm_update(reopen_state->bs);

}