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render: Avoid 0 or less animated cursors

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Animated cursors use a series of cursors that the client can set.

By default, the Xserver assumes at least one cursor is specified
while a client may actually pass no cursor at all.

That causes an out-of-bound read creating the animated cursor and a
crash of the Xserver:

 | Invalid read of size 8
 |    at 0x5323F4: AnimCursorCreate (animcur.c:325)
 |    by 0x52D4C5: ProcRenderCreateAnimCursor (render.c:1817)
 |    by 0x52DC80: ProcRenderDispatch (render.c:1999)
 |    by 0x4A1E9D: Dispatch (dispatch.c:560)
 |    by 0x4B0169: dix_main (main.c:284)
 |    by 0x4287F5: main (stubmain.c:34)
 |  Address 0x59aa010 is 0 bytes after a block of size 0 alloc'd
 |    at 0x48468D3: reallocarray (vg_replace_malloc.c:1803)
 |    by 0x52D3DA: ProcRenderCreateAnimCursor (render.c:1802)
 |    by 0x52DC80: ProcRenderDispatch (render.c:1999)
 |    by 0x4A1E9D: Dispatch (dispatch.c:560)
 |    by 0x4B0169: dix_main (main.c:284)
 |    by 0x4287F5: main (stubmain.c:34)
 |
 | Invalid read of size 2
 |    at 0x5323F7: AnimCursorCreate (animcur.c:325)
 |    by 0x52D4C5: ProcRenderCreateAnimCursor (render.c:1817)
 |    by 0x52DC80: ProcRenderDispatch (render.c:1999)
 |    by 0x4A1E9D: Dispatch (dispatch.c:560)
 |    by 0x4B0169: dix_main (main.c:284)
 |    by 0x4287F5: main (stubmain.c:34)
 |  Address 0x8 is not stack'd, malloc'd or (recently) free'd

To avoid the issue, check the number of cursors specified and return a
BadValue error in both the proc handler (early) and the animated cursor
creation (as this is a public function) if there is 0 or less cursor.

CVE-2025-49175

This issue was discovered by Nils Emmerich <nemmerich@ernw.de> and
reported by Julian Suleder via ERNW Vulnerability Disclosure.

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Reviewed-by: José Expósito <jexposit@redhat.com>
(cherry picked from commit 0885e0b262)

Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/2026>
This commit is contained in:
Olivier Fourdan 2025-03-28 09:43:52 +01:00
parent 34ef671aa5
commit fa6b40037a
2 changed files with 5 additions and 0 deletions
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3
render/animcur.c
View file

@ -304,6 +304,9 @@ AnimCursorCreate(CursorPtr *cursors, CARD32 *deltas, int ncursor,
int rc = BadAlloc, i;
AnimCurPtr ac;
if (ncursor <= 0)
return BadValue;
for (i = 0; i < screenInfo.numScreens; i++)
if (!GetAnimCurScreen(screenInfo.screens[i]))
return BadImplementation;

2
render/render.c
View file

@ -1795,6 +1795,8 @@ ProcRenderCreateAnimCursor(ClientPtr client)
ncursor =
(client->req_len -
(bytes_to_int32(sizeof(xRenderCreateAnimCursorReq)))) >> 1;
if (ncursor <= 0)
return BadValue;
cursors = xallocarray(ncursor, sizeof(CursorPtr) + sizeof(CARD32));
if (!cursors)
return BadAlloc;