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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id i7-20020a170902c94700b001754064ac31sm1720685pla.280.2022.09.27.08.37.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 27 Sep 2022 08:37:10 -0700 (PDT) From: Kees Cook To: Jamal Hadi Salim Cc: Kees Cook , Eric Dumazet , Cong Wang , Jiri Pirko , "David S. Miller" , Jakub Kicinski , Paolo Abeni , netdev@vger.kernel.org, syzbot+a2c4601efc75848ba321@syzkaller.appspotmail.com, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: [PATCH] net: sched: cls_u32: Avoid memcpy() false-positive warning Date: Tue, 27 Sep 2022 08:37:01 -0700 Message-Id: <20220927153700.3071688-1-keescook@chromium.org> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=1780; h=from:subject; bh=a5kfZGJ20b02uPWXgL+F0pZhrLA3yDR5ugsapwWzdVQ=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBjMxibiOsVeOwkPIgAZeyeGKuoXXag6IdhCVwdK/mY wPyLQjGJAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCYzMYmwAKCRCJcvTf3G3AJriyEA CPC7YSelum/IEpcDi7K97nEgWYsr8mtNQH1474+2H4xJLyhNW3HAMl1vTyCeMjvYmOD1aYN0xQ5teM LmKF6oPT44UK0btmPpAVOqyGNOV3/R8NvRRcCt3I/qv3AsQP6Ly3Ah4jaCYlNE5DYQsG+coJVVmJB7 535LwZTqcC9rI4xRNGfLr8af/UnLd9FGt2KbBnZ4NK5hiTgDET1qGYwK+EmgBpRtJZgN+SeagpND1b EdSXKgo7Zouz8Sh7xgWTYmHvOPDAbC3nb+oUmd+tg3rw9i2Cztj3UVHhxf8jQFJ1PNSi8Szmw5Edh/ DWl13x831rcqnPaIuaT8Abt4L+ypjwZZ6flOQxYCXGR5uIwLZBlpH65AMJJgRsZSsUJDrZd62N5V2w S39qNbLuiohGb+gBSPI/UpLSN5z1HeVvMkK+CfXq9Y7/R5xGKstH/COHXZDSoWjHNwYWV3xNeDWLCx 2JeNqT5Nfh7dI7MK6/RowSVlm4wFzOV+8sGJHeYY55Hebx8Ss4SGDx0VPWHJEVg9dEvIFJ/yARARp4 WEPBLJ2t2ncEXWLliNDmYK1gx6DaajGEZjW/c65rTBOUXqMA/r/6XPr38JGNyvHOiMyMfMQg+b2rE6 KknkWeeGmjYq1ZOABLLYpRno65rTj6e23knzZGqxvCR7zLXEsNl3ci2t24ZA== X-Developer-Key: i=keescook@chromium.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 Precedence: bulk List-ID: X-Mailing-List: linux-hardening@vger.kernel.org To work around a misbehavior of the compiler's ability to see into composite flexible array structs (as detailed in the coming memcpy() hardening series[1]), use unsafe_memcpy(), as the sizing, bounds-checking, and allocation are all very tightly coupled here. This silences the false-positive reported by syzbot: memcpy: detected field-spanning write (size 80) of single field "&n->sel" at net/sched/cls_u32.c:1043 (size 16) [1] https://lore.kernel.org/linux-hardening/20220901065914.1417829-2-keescook@chromium.org Cc: Jamal Hadi Salim Cc: Eric Dumazet Cc: Cong Wang Cc: Jiri Pirko Cc: "David S. Miller" Cc: Jakub Kicinski Cc: Paolo Abeni Cc: netdev@vger.kernel.org Reported-by: syzbot+a2c4601efc75848ba321@syzkaller.appspotmail.com Link: https://lore.kernel.org/lkml/000000000000a96c0b05e97f0444@google.com/ Signed-off-by: Kees Cook Reviewed-by: Jamal Hadi Salim --- net/sched/cls_u32.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c index 4d27300c287c..5f33472aad36 100644 --- a/net/sched/cls_u32.c +++ b/net/sched/cls_u32.c @@ -1040,7 +1040,11 @@ static int u32_change(struct net *net, struct sk_buff *in_skb, } #endif - memcpy(&n->sel, s, sel_size); + unsafe_memcpy(&n->sel, s, sel_size, + /* A composite flex-array structure destination, + * which was correctly sized with struct_size(), + * bounds-checked against nla_len(), and allocated + * above. */); RCU_INIT_POINTER(n->ht_up, ht); n->handle = handle; n->fshift = s->hmask ? ffs(ntohl(s->hmask)) - 1 : 0;