From: Davide Ornaghi Date: Wed, 10 Jun 2026 10:39:13 +0000 (+0200) Subject: netfilter: nft_meta_bridge: fix stale stack leak via IIFHWADDR register X-Git-Url: http://git.ipfire.org/gitweb/?a=commitdiff_plain;h=c7d573551f9286100a055ef696cde6af54549677;p=thirdparty%2Fkernel%2Flinux.git netfilter: nft_meta_bridge: fix stale stack leak via IIFHWADDR register NFT_META_BRI_IIFHWADDR declares its destination register with len = ETH_ALEN (6 bytes), which the register-init tracking rounds up to two 32-bit registers (8 bytes). nft_meta_bridge_get_eval() then does memcpy(dest, br_dev->dev_addr, ETH_ALEN), writing only 6 bytes and leaving the upper 2 bytes of the second register as uninitialised nft_do_chain() stack. A downstream load of that register span leaks those stale bytes to userspace. Zero the second register before the memcpy so the full declared span is written. Fixes: cbd2257dc96e ("netfilter: nft_meta_bridge: introduce NFT_META_BRI_IIFHWADDR support") Cc: stable@vger.kernel.org Signed-off-by: Davide Ornaghi Signed-off-by: Pablo Neira Ayuso --- diff --git a/net/bridge/netfilter/nft_meta_bridge.c b/net/bridge/netfilter/nft_meta_bridge.c index 7763e78abb00..219c40680260 100644 --- a/net/bridge/netfilter/nft_meta_bridge.c +++ b/net/bridge/netfilter/nft_meta_bridge.c @@ -64,6 +64,8 @@ static void nft_meta_bridge_get_eval(const struct nft_expr *expr, if (!br_dev) goto err; + /* ETH_ALEN (6) is shorter than the destination register span (8) */ + dest[1] = 0; memcpy(dest, br_dev->dev_addr, ETH_ALEN); return; default: