lkml.org 
[lkml]   [2022]   [Sep]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [syzbot] WARNING in u32_change
On Sun, Sep 25, 2022 at 10:34:37AM -0700, Eric Dumazet wrote:
> Sure, please look at:
>
> commit 54d9469bc515dc5fcbc20eecbe19cea868b70d68
> Author: Kees Cook <keescook@chromium.org>
> Date: Thu Jun 24 15:39:26 2021 -0700
>
> fortify: Add run-time WARN for cross-field memcpy()
> [...]
> Here, we might switch to unsafe_memcpy() instead of memcpy()

I would tend to agree. Something like:

diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
index 4d27300c287c..21e0e6206ecc 100644
--- a/net/sched/cls_u32.c
+++ b/net/sched/cls_u32.c
@@ -1040,7 +1040,9 @@ 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 and allocated above. */);
RCU_INIT_POINTER(n->ht_up, ht);
n->handle = handle;
n->fshift = s->hmask ? ffs(ntohl(s->hmask)) - 1 : 0;
This alloc/partial-copy pattern is relatively common in the kernel, so
I've been considering adding a helper for it. It'd be like kmemdup(),
but more like kmemdup_offset(), which only the object from a certainly
point is copied.

--
Kees Cook

\
 
 \ /
  Last update: 2022-09-26 04:39    [W:0.194 / U:0.120 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site