From 4794b5dd34688158fb51a2943032569d3780c4b8 Mon Sep 17 00:00:00 2001 From: Tobias Stoeckmann Date: Sat, 21 Oct 2017 23:47:52 +0200 Subject: [PATCH] Fix heap overflows when parsing malicious files. (CVE-2017-16612) It is possible to trigger heap overflows due to an integer overflow while parsing images and a signedness issue while parsing comments. The integer overflow occurs because the chosen limit 0x10000 for dimensions is too large for 32 bit systems, because each pixel takes 4 bytes. Properly chosen values allow an overflow which in turn will lead to less allocated memory than needed for subsequent reads. The signedness bug is triggered by reading the length of a comment as unsigned int, but casting it to int when calling the function XcursorCommentCreate. Turning length into a negative value allows the check against XCURSOR_COMMENT_MAX_LEN to pass, and the following addition of sizeof (XcursorComment) + 1 makes it possible to allocate less memory than needed for subsequent reads. CVE: CVE-2017-16612 Upstream-Status: Backport [https://cgit.freedesktop.org/xorg/lib/libXcursor/commit/?id=4794b5dd34688158fb51a2943032569d3780c4b8] Signed-off-by: Tobias Stoeckmann Reviewed-by: Matthieu Herrb Signed-off-by: Andreas Wellving --- src/file.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/src/file.c b/src/file.c index 43163c2..da16277 100644 --- a/src/file.c +++ b/src/file.c @@ -29,6 +29,11 @@ XcursorImageCreate (int width, int height) { XcursorImage *image; + if (width < 0 || height < 0) + return NULL; + if (width > XCURSOR_IMAGE_MAX_SIZE || height > XCURSOR_IMAGE_MAX_SIZE) + return NULL; + image = malloc (sizeof (XcursorImage) + width * height * sizeof (XcursorPixel)); if (!image) @@ -101,7 +106,7 @@ XcursorCommentCreate (XcursorUInt comment_type, int length) { XcursorComment *comment; - if (length > XCURSOR_COMMENT_MAX_LEN) + if (length < 0 || length > XCURSOR_COMMENT_MAX_LEN) return NULL; comment = malloc (sizeof (XcursorComment) + length + 1); @@ -448,7 +453,8 @@ _XcursorReadImage (XcursorFile *file, if (!_XcursorReadUInt (file, &head.delay)) return NULL; /* sanity check data */ - if (head.width >= 0x10000 || head.height > 0x10000) + if (head.width > XCURSOR_IMAGE_MAX_SIZE || + head.height > XCURSOR_IMAGE_MAX_SIZE) return NULL; if (head.width == 0 || head.height == 0) return NULL; @@ -457,6 +463,8 @@ _XcursorReadImage (XcursorFile *file, /* Create the image and initialize it */ image = XcursorImageCreate (head.width, head.height); + if (image == NULL) + return NULL; if (chunkHeader.version < image->version) image->version = chunkHeader.version; image->size = chunkHeader.subtype; -- 2.7.4