From f64042620963059859d0bbae60e8655ccc44736e Mon Sep 17 00:00:00 2001
From: Kevin Wolf <kwolf@redhat.com>
Date: Fri, 15 Mar 2019 18:10:01 +0100
Subject: [PATCH 005/163] block: Make permission changes in reopen less wrong

RH-Author: Kevin Wolf <kwolf@redhat.com>
Message-id: <20190315181010.14964-6-kwolf@redhat.com>
Patchwork-id: 84882
O-Subject: [RHEL-7.7 qemu-kvm-rhev PATCH 05/14] block: Make permission changes in reopen less wrong
Bugzilla: 1685989
RH-Acked-by: John Snow <jsnow@redhat.com>
RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>

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: Kevin Wolf <kwolf@redhat.com>
(cherry picked from commit 69b736e76567ecbc9b9e55570bc0afc840614a98)
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 block.c | 35 ++++++++++++++++++++++++-----------
 1 file changed, 24 insertions(+), 11 deletions(-)

diff --git a/block.c b/block.c
index 2f1b4d1..b31124c 100644
--- a/block.c
+++ b/block.c
@@ -1661,6 +1661,7 @@ 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;
@@ -3072,6 +3073,16 @@ 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
      */
@@ -3080,7 +3091,20 @@ 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) {
@@ -3297,12 +3321,6 @@ 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;
 
 error:
@@ -3352,9 +3370,6 @@ 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) {
@@ -3386,8 +3401,6 @@ 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);
 }
 
 
-- 
1.8.3.1