From fe11e5c40817b84abaa5d83bfb6586d8412bfd07 Mon Sep 17 00:00:00 2001 From: Kai Ma Date: Wed, 22 Apr 2026 22:54:18 +0800 Subject: [PATCH] netfilter: reject zero shift in nft_bitwise Reject zero shift operands for nft_bitwise left and right shift expressions during initialization. The carry propagation logic computes the carry from the adjacent 32-bit word using BITS_PER_TYPE(u32) - shift. A zero shift operand turns this into a 32-bit shift, which is undefined behaviour. Reject zero shift operands in the control plane, alongside the existing check for values greater than or equal to 32, so malformed rules never reach the packet path. Fixes: 567d746b55bc ("netfilter: bitwise: add support for shifts.") Cc: stable@kernel.org Reported-by: Yuan Tan Reported-by: Yifan Wu Reported-by: Juefei Pu Reported-by: Xin Liu Signed-off-by: Kai Ma Signed-off-by: Ren Wei Reviewed-by: Fernando Fernandez Mancera Signed-off-by: Pablo Neira Ayuso --- net/netfilter/nft_bitwise.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/net/netfilter/nft_bitwise.c b/net/netfilter/nft_bitwise.c index 13808e9cd999..94dccdcfa06b 100644 --- a/net/netfilter/nft_bitwise.c +++ b/net/netfilter/nft_bitwise.c @@ -196,7 +196,8 @@ static int nft_bitwise_init_shift(struct nft_bitwise *priv, if (err < 0) return err; - if (priv->data.data[0] >= BITS_PER_TYPE(u32)) { + if (!priv->data.data[0] || + priv->data.data[0] >= BITS_PER_TYPE(u32)) { nft_data_release(&priv->data, desc.type); return -EINVAL; }