[Libguestfs] [PATCH hivex] lib/node.c: Limit recursion in ri-records (CVE-2021-3622)

Windows Registry hive "ri"-records are arbitrarily nested B-tree-like structures: +-------------+ | ri | |-------------| | nr_offsets | | offset[0] ------> points to another lf/lh/li/ri block | offset[1] ------> | offset[2] ------> +-------------+ It is possible to construct a hive with a very deeply nested tree of ri-records, causing the internal _get_children function to recurse to any depth which can cause programs linked to hivex to crash with a stack overflow. Since it is not thought that deeply nested ri-records occur in real hives, limit recursion depth. If you hit this limit you will see the following error and the operation will return an error instead of crashing: \> ls hivex: _get_children: returning EINVAL because: ri-record nested to depth >= 32 ls: Invalid argument Thanks to Jeremy Galindo for finding and reporting this bug. Reported-by: Jeremy Galindo, Sr Security Engineer, Datto.com Signed-off-by: Richard W.M. Jones <rjones(a)redhat.com&gt; Fixes: CVE-2021-3622 Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1975489 (cherry picked from commit 781a12c4a49dd81365c9c567c5aa5e19e894ba0e) --- lib/node.c | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-) diff --git a/lib/node.c b/lib/node.c index 7b002a46..eb7fe93c 100644 --- a/lib/node.c +++ b/lib/node.c @@ -203,7 +203,7 @@ hivex_node_classname (hive_h *h, hive_node_h node) static int _get_children (hive_h *h, hive_node_h blkoff, offset_list *children, offset_list *blocks, - int flags); + int flags, unsigned depth); static int check_child_is_nk_block (hive_h *h, hive_node_h child, int flags); /* Iterate over children (ie. subkeys of a node), returning child @@ -335,7 +335,7 @@ _hivex_get_children (hive_h *h, hive_node_h node, goto error; } - if (_get_children (h, subkey_lf, &children, &blocks, flags) == -1) + if (_get_children (h, subkey_lf, &children, &blocks, flags, 0) == -1) goto error; /* Check the number of children we ended up reading matches @@ -383,7 +383,7 @@ _hivex_get_children (hive_h *h, hive_node_h node, static int _get_children (hive_h *h, hive_node_h blkoff, offset_list *children, offset_list *blocks, - int flags) + int flags, unsigned depth) { /* Add this intermediate block. */ if (_hivex_add_to_offset_list (blocks, blkoff) == -1) @@ -486,7 +486,17 @@ _get_children (hive_h *h, hive_node_h blkoff, } } - if (_get_children (h, offset, children, blocks, flags) == -1) + /* Although in theory hive ri records might be nested to any + * depth, in practice this is unlikely. Recursing here caused + * CVE-2021-3622. Thus limit the depth we will recurse to + * something small. + */ + if (depth >= 32) { + SET_ERRNO (EINVAL, "ri-record nested to depth >= %u", depth); + return -1; + } + + if (_get_children (h, offset, children, blocks, flags, depth+1) == -1) return -1; } } -- 2.32.0