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From 61f4928dcc31b91aaf3bcbcf2898f8f09586a213 Mon Sep 17 00:00:00 2001
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From: "Richard W.M. Jones" <rjones@redhat.com>
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Date: Thu, 15 Apr 2021 15:50:13 +0100
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Subject: [PATCH] lib/handle.c: Bounds check for block exceeding page length
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(CVE-2021-3504)
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Hives are encoded as fixed-sized pages containing smaller variable-
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length blocks:
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+-------------------+-------------------+-------------------+--
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| header |[ blk ][blk][ blk ]|[blk][blk][blk] |
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+-------------------+-------------------+-------------------+--
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Blocks should not straddle a page boundary. However because blocks
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contain a 32 bit length field it is possible to construct an invalid
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hive where the last block in a page overlaps either the next page or
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the end of the file:
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+-------------------+-------------------+
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| header |[ blk ][blk][ blk ..... ]
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+-------------------+-------------------+
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Hivex lacked a bounds check and would process the registry. Because
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the rest of the code assumes this situation can never happen it was
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possible to have a block containing some field (eg. a registry key
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name) which would extend beyond the end of the file. Hivex mmaps or
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mallocs the file, causing hivex to read memory beyond the end of the
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mapped region, resulting in reading other memory structures or a
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crash. (Writing beyond the end of the mapped region seems to be
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impossible because we always allocate a new page before writing.)
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This commit adds a check which rejects the malformed registry on
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hivex_open.
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Credit: Jeremy Galindo, Sr Security Engineer, Datto.com
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Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
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Fixes: CVE-2021-3504
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Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1949687
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---
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lib/handle.c | 12 ++++++++++--
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1 file changed, 10 insertions(+), 2 deletions(-)
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diff --git a/lib/handle.c b/lib/handle.c
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index 88b1563f..2e4231a5 100644
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--- a/lib/handle.c
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+++ b/lib/handle.c
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@@ -353,8 +353,8 @@ hivex_open (const char *filename, int flags)
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#pragma GCC diagnostic pop
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if (is_root || !h->unsafe) {
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SET_ERRNO (ENOTSUP,
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- "%s, the block at 0x%zx has invalid size %" PRIu32
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- ", bad registry",
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+ "%s, the block at 0x%zx size %" PRIu32
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+ " <= 4 or not a multiple of 4, bad registry",
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filename, blkoff, le32toh (block->seg_len));
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goto error;
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} else {
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@@ -365,6 +365,14 @@ hivex_open (const char *filename, int flags)
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}
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}
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+ if (blkoff + seg_len > off + page_size) {
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+ SET_ERRNO (ENOTSUP,
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+ "%s, the block at 0x%zx size %" PRIu32
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+ " extends beyond the current page, bad registry",
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+ filename, blkoff, le32toh (block->seg_len));
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+ goto error;
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+ }
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+
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if (h->msglvl >= 2) {
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unsigned char *id = (unsigned char *) block->id;
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int id0 = id[0], id1 = id[1];
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--
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2.29.2
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