From: Weiming Shi <[email protected]> bpf_msg_push_data() allocates pages via alloc_pages() without __GFP_ZERO. In the non-copy path, the entire page of uninitialized heap content is added directly to the sk_msg scatterlist, which is then transmitted over TCP to userspace via tcp_bpf_push(). In the copy path, a gap of len bytes between the front and back memcpy regions is similarly left uninitialized.
This leads to a kernel heap information leak: stale page content including kernel pointers from the direct-map and vmemmap regions is transmitted to userspace, which can be used to defeat KASLR. Add __GFP_ZERO to the alloc_pages() call to ensure the allocated page is always zeroed before it enters the scatterlist. Link: https://lore.kernel.org/all/[email protected] Fixes: 6fff607e2f14 ("bpf: sk_msg program helper bpf_msg_push_data") Tested-by: Xiang Mei <[email protected]> Tested-by: Xinyu Ma <[email protected]> Reviewed-by: Jiayuan Chen <[email protected]> Reviewed-by: Emil Tsalapatis <[email protected]> Signed-off-by: Weiming Shi <[email protected]> Signed-off-by: Jiayuan Chen <[email protected]> --- net/core/filter.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/core/filter.c b/net/core/filter.c index 3e555f276ba80..6e345ca65ca14 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -2832,7 +2832,7 @@ BPF_CALL_4(bpf_msg_push_data, struct sk_msg *, msg, u32, start, if (unlikely(copy + len < copy)) return -EINVAL; - page = alloc_pages(__GFP_NOWARN | GFP_ATOMIC | __GFP_COMP, + page = alloc_pages(__GFP_NOWARN | GFP_ATOMIC | __GFP_COMP | __GFP_ZERO, get_order(copy + len)); if (unlikely(!page)) return -ENOMEM; -- 2.43.0
