70 lines
2.3 KiB
Diff
70 lines
2.3 KiB
Diff
From 1932abe3d0db719b0676afdad14f1716ef9387ee Mon Sep 17 00:00:00 2001
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From: Olivier Fourdan <ofourdan@redhat.com>
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Date: Mon, 20 Jan 2025 16:52:01 +0100
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Subject: [PATCH xserver 10/13] sync: Do not let sync objects uninitialized
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When changing an alarm, the change mask values are evaluated one after
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the other, changing the trigger values as requested and eventually,
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SyncInitTrigger() is called.
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SyncInitTrigger() will evaluate the XSyncCACounter first and may free
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the existing sync object.
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Other changes are then evaluated and may trigger an error and an early
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return, not adding the new sync object.
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This can be used to cause a use after free when the alarm eventually
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triggers.
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To avoid the issue, delete the existing sync object as late as possible
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only once we are sure that no further error will cause an early exit.
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CVE-2025-26601, ZDI-CAN-25870
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This vulnerability was discovered by:
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Jan-Niklas Sohn working with Trend Micro Zero Day Initiative
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Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
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Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
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(cherry picked from commit 16a1242d0ffc7f45ed3c595ee7564b5c04287e0b)
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Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/1831>
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---
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Xext/sync.c | 13 ++++++++-----
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1 file changed, 8 insertions(+), 5 deletions(-)
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diff --git a/Xext/sync.c b/Xext/sync.c
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index 8da5bf616..1c186095d 100644
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--- a/Xext/sync.c
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+++ b/Xext/sync.c
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@@ -330,11 +330,6 @@ SyncInitTrigger(ClientPtr client, SyncTrigger * pTrigger, XID syncObject,
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client->errorValue = syncObject;
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return rc;
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}
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- if (pSync != pTrigger->pSync) { /* new counter for trigger */
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- SyncDeleteTriggerFromSyncObject(pTrigger);
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- pTrigger->pSync = pSync;
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- newSyncObject = TRUE;
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- }
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}
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/* if system counter, ask it what the current value is */
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@@ -402,6 +397,14 @@ SyncInitTrigger(ClientPtr client, SyncTrigger * pTrigger, XID syncObject,
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}
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}
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+ if (changes & XSyncCACounter) {
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+ if (pSync != pTrigger->pSync) { /* new counter for trigger */
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+ SyncDeleteTriggerFromSyncObject(pTrigger);
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+ pTrigger->pSync = pSync;
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+ newSyncObject = TRUE;
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+ }
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+ }
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+
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/* we wait until we're sure there are no errors before registering
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* a new counter on a trigger
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*/
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--
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2.48.1
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