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From 0dab0b527ac5c4fe0272ea679522bd87238a733b Mon Sep 17 00:00:00 2001
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From: Peter Hutterer <peter.hutterer@who-t.net>
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Date: Tue, 29 Nov 2022 13:55:32 +1000
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Subject: [PATCH xserver 4/7] Xi: disallow passive grabs with a detail > 255
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The XKB protocol effectively prevents us from ever using keycodes above
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255. For buttons it's theoretically possible but realistically too niche
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to worry about. For all other passive grabs, the detail must be zero
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anyway.
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This fixes an OOB write:
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ProcXIPassiveUngrabDevice() calls DeletePassiveGrabFromList with a
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temporary grab struct which contains tempGrab->detail.exact = stuff->detail.
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For matching existing grabs, DeleteDetailFromMask is called with the
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stuff->detail value. This function creates a new mask with the one bit
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representing stuff->detail cleared.
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However, the array size for the new mask is 8 * sizeof(CARD32) bits,
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thus any detail above 255 results in an OOB array write.
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CVE-2022-46341, ZDI-CAN 19381
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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: Peter Hutterer <peter.hutterer@who-t.net>
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Acked-by: Olivier Fourdan <ofourdan@redhat.com>
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---
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Xi/xipassivegrab.c | 12 ++++++++++++
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1 file changed, 12 insertions(+)
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diff --git a/Xi/xipassivegrab.c b/Xi/xipassivegrab.c
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index 65d5870f6f..89a591098a 100644
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--- a/Xi/xipassivegrab.c
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+++ b/Xi/xipassivegrab.c
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@@ -133,6 +133,12 @@ ProcXIPassiveGrabDevice(ClientPtr client)
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return BadValue;
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}
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+ /* XI2 allows 32-bit keycodes but thanks to XKB we can never
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+ * implement this. Just return an error for all keycodes that
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+ * cannot work anyway, same for buttons > 255. */
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+ if (stuff->detail > 255)
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+ return XIAlreadyGrabbed;
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+
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if (XICheckInvalidMaskBits(client, (unsigned char *) &stuff[1],
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stuff->mask_len * 4) != Success)
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return BadValue;
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@@ -313,6 +319,12 @@ ProcXIPassiveUngrabDevice(ClientPtr client)
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return BadValue;
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}
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+ /* We don't allow passive grabs for details > 255 anyway */
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+ if (stuff->detail > 255) {
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+ client->errorValue = stuff->detail;
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+ return BadValue;
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+ }
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+
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rc = dixLookupWindow(&win, stuff->grab_window, client, DixSetAttrAccess);
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if (rc != Success)
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return rc;
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--
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2.38.1
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