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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Daniel Axtens <dja@axtens.net>
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Date: Thu, 21 Jan 2021 12:20:49 +1100
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Subject: [PATCH] io/gzio: Catch missing values in huft_build() and bail
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In huft_build(), "v" is a table of values in order of bit length.
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The code later (when setting up table entries in "r") assumes that all
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elements of this array corresponding to a code are initialized and less
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than N_MAX. However, it doesn't enforce this.
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With sufficiently manipulated inputs (e.g. from fuzzing), there can be
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elements of "v" that are not filled. Therefore a lookup into "e" or "d"
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will use an uninitialized value. This can lead to an invalid/OOB read on
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those values, often leading to a crash.
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Signed-off-by: Daniel Axtens <dja@axtens.net>
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Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
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---
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grub-core/io/gzio.c | 10 +++++++++-
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1 file changed, 9 insertions(+), 1 deletion(-)
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diff --git a/grub-core/io/gzio.c b/grub-core/io/gzio.c
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index d3b12a61e61..3e14347827b 100644
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--- a/grub-core/io/gzio.c
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+++ b/grub-core/io/gzio.c
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@@ -495,6 +495,7 @@ huft_build (unsigned *b, /* code lengths in bits (all assumed <= BMAX) */
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}
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/* Make a table of values in order of bit lengths */
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+ grub_memset (v, N_MAX, ARRAY_SIZE (v));
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p = b;
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i = 0;
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do
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@@ -576,11 +577,18 @@ huft_build (unsigned *b, /* code lengths in bits (all assumed <= BMAX) */
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r.v.n = (ush) (*p); /* simple code is just the value */
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p++; /* one compiler does not like *p++ */
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}
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- else
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+ else if (*p < N_MAX)
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{
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r.e = (uch) e[*p - s]; /* non-simple--look up in lists */
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r.v.n = d[*p++ - s];
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}
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+ else
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+ {
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+ /* Detected an uninitialised value, abort. */
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+ if (h)
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+ huft_free (u[0]);
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+ return 2;
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+ }
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/* fill code-like entries with r */
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f = 1 << (k - w);
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