63 lines
2.6 KiB
Diff
63 lines
2.6 KiB
Diff
From b1f0827c30f59a2dcbc8a39e42cace7a1de35f7f Mon Sep 17 00:00:00 2001
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From: Ken Sharp <Ken.Sharp@artifex.com>
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Date: Mon, 2 Sep 2024 15:14:01 +0100
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Subject: [PATCH] PDF interpreter - sanitise W array values in Xref streams
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Bug #708001 "Buffer overflow in PDF XRef stream"
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See bug report. I've chosen to fix this by checking the values in the
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W array; these can (currently at least) only have certain relatively
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small values.
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As a future proofing fix I've also updated field_size in
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pdf_xref_stream_entries() to be a 64-bit integer. This is far bigger
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than required, but matches the W array values and so prevents the
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mismatch which could lead to a buffer overrun.
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CVE-2024-46952
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---
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pdf/pdf_xref.c | 20 +++++++++++++++++++-
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1 file changed, 19 insertions(+), 1 deletion(-)
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diff --git a/pdf/pdf_xref.c b/pdf/pdf_xref.c
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index fefd08abe..4ad0f548f 100644
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--- a/pdf/pdf_xref.c
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+++ b/pdf/pdf_xref.c
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@@ -53,7 +53,7 @@ static int resize_xref(pdf_context *ctx, uint64_t new_size)
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static int read_xref_stream_entries(pdf_context *ctx, pdf_c_stream *s, int64_t first, int64_t last, int64_t *W)
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{
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uint i, j;
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- uint field_width = 0;
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+ uint64_t field_width = 0;
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uint32_t type = 0;
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uint64_t objnum = 0, gen = 0;
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byte *Buffer;
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@@ -305,6 +305,24 @@ static int pdfi_process_xref_stream(pdf_context *ctx, pdf_stream *stream_obj, pd
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}
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pdfi_countdown(a);
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+ /* W[0] is either:
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+ * 0 (no type field) or a single byte with the type.
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+ * W[1] is either:
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+ * The object number of the next free object, the byte offset of this object in the file or the object5 number of the object stream where this object is stored.
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+ * W[2] is either:
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+ * The generation number to use if this object is used again, the generation number of the object or the index of this object within the object stream.
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+ *
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+ * Object and generation numbers are limited to unsigned 64-bit values, as are bytes offsets in the file, indexes of objects within the stream likewise (actually
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+ * most of these are generally 32-bit max). So we can limit the field widths to 8 bytes, enough to hold a 64-bit number.
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+ * Even if a later version of the spec makes these larger (which seems unlikely!) we still cna't cope with integers > 64-bits.
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+ */
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+ if (W[0] > 1 || W[1] > 8 || W[2] > 8) {
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+ pdfi_close_file(ctx, XRefStrm);
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+ pdfi_countdown(ctx->xref_table);
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+ ctx->xref_table = NULL;
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+ return code;
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+ }
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+
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code = pdfi_dict_get_type(ctx, sdict, "Index", PDF_ARRAY, (pdf_obj **)&a);
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if (code == gs_error_undefined) {
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code = read_xref_stream_entries(ctx, XRefStrm, 0, size - 1, W);
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--
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2.49.0
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