60 lines
2.3 KiB
Diff
60 lines
2.3 KiB
Diff
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From d69dd6b341594c338fa6c7b327fd7f201eb37bc1 Mon Sep 17 00:00:00 2001
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From: Uli Schlachter <psychon@znc.in>
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Date: Sat, 18 Jun 2016 15:08:52 +0200
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Subject: [PATCH] xlib: Fix double free in _get_image_surface()
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If XShmGetImage() fails, the code tries to continue with its normal,
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non-shared-memory path. However, the image variable, which was previously set to
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NULL, now points to an already-destroyed surface, causing a double-free when the
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function cleans up after itself (actually, its an assertion failure because the
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reference count of the surface is zero, but technically this is still a double
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free).
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Fix this by setting image=NULL after destroying the surface that this refers to,
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to make sure this surface will not be destroyed again.
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While we are here (multiple changes in a single commit are bad...), also fix the
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cleanup done in bail. In practice, &image->base should be safe when image==NULL,
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because this just adds some offset to the pointer (the offset here is actually
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zero, so this doesn't do anything at all). However, the C standard does not
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require this to be safe, so let's handle this case specially.
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Note that anything that is fixed by this change is still buggy, because the only
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reason why XShmGetImage() could fail would be BadDrawable, meaning that the
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target we draw to does not exist or was already destroyed. This patch will
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likely just cause X11 errors elsewhere and drawing to (possible) invalid
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drawables is not supported by cairo anyway. This means that if SHM fails, the
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following fallback code has a high chance of failing, too.
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Fixes: https://bugs.freedesktop.org/show_bug.cgi?id=91967
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Signed-off-by: Uli Schlachter <psychon@znc.in>
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---
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src/cairo-xlib-surface.c | 4 +++-
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1 file changed, 3 insertions(+), 1 deletion(-)
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diff --git a/src/cairo-xlib-surface.c b/src/cairo-xlib-surface.c
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index 3f407c3..555c1fe 100644
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--- a/src/cairo-xlib-surface.c
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+++ b/src/cairo-xlib-surface.c
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@@ -807,6 +807,7 @@ _get_image_surface (cairo_xlib_surface_t *surface,
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}
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cairo_surface_destroy (&image->base);
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+ image = NULL;
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}
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}
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@@ -1011,7 +1012,8 @@ _get_image_surface (cairo_xlib_surface_t *surface,
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cairo_device_release (&display->base);
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if (unlikely (status)) {
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- cairo_surface_destroy (&image->base);
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+ if (image)
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+ cairo_surface_destroy (&image->base);
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return _cairo_surface_create_in_error (status);
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}
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--
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2.7.4
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