net: sched: cls_u32: Avoid memcpy() false-positive warning in u32_init_knode()

Syzbot reported a warning in u32_init_knode() [1].

Similar to commit 7cba18332e36 ("net: sched: cls_u32: Avoid memcpy()
false-positive warning") which addressed the same issue in u32_change(),
use unsafe_memcpy() in u32_init_knode() to work around the compiler's
inability to see into composite flexible array structs.

This silences the false-positive reported by syzbot:

  memcpy: detected field-spanning write (size 32) of single field
  "&new->sel" at net/sched/cls_u32.c:855 (size 16)

Since the memory is correctly allocated with kzalloc_flex() using
s->nkeys, this is purely a false positive and does not need a Fixes tag.

[1] https://syzkaller.appspot.com/bug?extid=d5ace703ed883df56e42

Reported-by: syzbot+d5ace703ed883df56e42@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/69a811b9.a70a0220.b118c.0019.GAE@google.com/T/
Reviewed-by: Simon Horman <horms@kernel.org>
Acked-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Jiayuan Chen <jiayuan.chen@shopee.com>
Link: https://patch.msgid.link/20260309123917.402183-1-jiayuan.chen@linux.dev
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
index 9241c025aa741964080d895422795a7396ffb543..8f30cc82181d9cfbc0a6ea4c8e8775aa77708b5f 100644 (file)
--- a/net/sched/cls_u32.c
+++ b/net/sched/cls_u32.c
@@ -852,7 +852,10 @@ static struct tc_u_knode *u32_init_knode(struct net *net, struct tcf_proto *tp,
        /* Similarly success statistics must be moved as pointers */
        new->pcpu_success = n->pcpu_success;
 #endif
-       memcpy(&new->sel, s, struct_size(s, keys, s->nkeys));
+       unsafe_memcpy(&new->sel, s, struct_size(s, keys, s->nkeys),
+                     /* A composite flex-array structure destination,
+                      * which was correctly sized with kzalloc_flex(),
+                      * above. */);
 
        if (tcf_exts_init(&new->exts, net, TCA_U32_ACT, TCA_U32_POLICE)) {
                kfree(new);