Re: [PATCH net-next v1] net: sched: cls_u32: Avoid memcpy() false-positive warning in u32_init_knode()
From: Gustavo A. R. Silva <hidden>
Date: 2026-03-05 19:26:49
Also in:
linux-hardening, lkml
On 3/5/26 16:33, Jiayuan Chen wrote:
From: Jiayuan Chen <redacted>
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/ (local)
Signed-off-by: Jiayuan Chen <redacted>Acked-by: Gustavo A. R. Silva <gustavoars@kernel.org> Thanks -Gustavo
quoted hunk ↗ jump to hunk
Made-with: Cursor --- net/sched/cls_u32.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c index 9241c025aa74..8f30cc82181d 100644 --- 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);