linux-kernel - [PATCH 5.9 22/49] ethtool: fix stack overflow in ethnl_parse

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Date:   Sat, 19 Dec 2020 13:58:26 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        syzbot+9d39fa49d4df294aab93@...kaller.appspotmail.com,
        Michal Kubecek <mkubecek@...e.cz>,
        Jakub Kicinski <kuba@...nel.org>
Subject: [PATCH 5.9 22/49] ethtool: fix stack overflow in ethnl_parse_bitset()

From: Michal Kubecek <mkubecek@...e.cz>

[ Upstream commit a770bf515613c6e12ae904c3593e26016de99448 ]

Syzbot reported a stack overflow in bitmap_from_arr32() called from
ethnl_parse_bitset() when bitset from netlink message is longer than
target bitmap length. While ethnl_compact_sanity_checks() makes sure that
trailing part is all zeros (i.e. the request does not try to touch bits
kernel does not recognize), we also need to cap change_bits to nbits so
that we don't try to write past the prepared bitmaps.

Fixes: 88db6d1e4f62 ("ethtool: add ethnl_parse_bitset() helper")
Reported-by: syzbot+9d39fa49d4df294aab93@...kaller.appspotmail.com
Signed-off-by: Michal Kubecek <mkubecek@...e.cz>
Link: https://lore.kernel.org/r/3487ee3a98e14cd526f55b6caaa959d2dcbcad9f.1607465316.git.mkubecek@suse.cz
Signed-off-by: Jakub Kicinski <kuba@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/ethtool/bitset.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/net/ethtool/bitset.c
+++ b/net/ethtool/bitset.c
@@ -630,6 +630,8 @@ int ethnl_parse_bitset(unsigned long *va
 			return ret;
 
 		change_bits = nla_get_u32(tb[ETHTOOL_A_BITSET_SIZE]);
+		if (change_bits > nbits)
+			change_bits = nbits;
 		bitmap_from_arr32(val, nla_data(tb[ETHTOOL_A_BITSET_VALUE]),
 				  change_bits);
 		if (change_bits < nbits)