From: Cen Zhang (Microsoft) Date: Thu, 23 Jul 2026 04:49:55 +0000 (-0400) Subject: net/sched: cls_u32: validate offshift to prevent shift-out-of-bounds X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=aef96eead2860cbfa371e4471d4f04412213b958;p=thirdparty%2Fkernel%2Fstable.git net/sched: cls_u32: validate offshift to prevent shift-out-of-bounds u32_change() copies the user-provided tc_u32_sel.offshift (unsigned char, 0-255) into the kernel knode object without bounds validation. When a packet later hits u32_classify() with TC_U32_VAROFFSET set, it evaluates `ntohs(offmask & *data) >> offshift` where the left operand is a 16-bit value promoted to a 32-bit int. Any offshift >= 32 is undefined behavior per C11 6.5.7p3, triggerable by an unprivileged user via user/network namespaces. UBSAN: shift-out-of-bounds in net/sched/cls_u32.c:236:43 shift exponent 32 is too large for 32-bit type int Fix this by rejecting offshift >= 16 during filter creation in u32_change(). Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Reported-by: AutonomousCodeSecurity@microsoft.com Link: https://lore.kernel.org/all/20260720034514.23053-1-blbllhy@gmail.com Signed-off-by: Cen Zhang (Microsoft) Acked-by: Jamal Hadi Salim Tested-by: Jamal Hadi Salim Tested-by: Victor Nogueira Link: https://patch.msgid.link/20260723044955.89471-1-blbllhy@gmail.com Signed-off-by: Paolo Abeni --- diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c index 8f30cc82181d..ac98b1c2144a 100644 --- a/net/sched/cls_u32.c +++ b/net/sched/cls_u32.c @@ -1107,6 +1107,13 @@ static int u32_change(struct net *net, struct sk_buff *in_skb, goto erridr; } + if (s->offshift >= 16) { + NL_SET_ERR_MSG_MOD(extack, + "offshift must be less than 16"); + err = -EINVAL; + goto erridr; + } + n = kzalloc_flex(*n, sel.keys, s->nkeys); if (n == NULL) { err = -ENOBUFS;