[PATCH bpf 3/4] bpf, sockmap: zero-initialize pages allocated in bpf_msg_push_data

[Jiayuan Chen <jiayuan.chen@linux.dev>]

From: Weiming Shi <bestswngs@gmail.com>

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/20260424155913.A19FDC19425@smtp.kernel.org
Fixes: 6fff607e2f14 ("bpf: sk_msg program helper bpf_msg_push_data")
Tested-by: Xiang Mei <xmei5@asu.edu>
Tested-by: Xinyu Ma <mmmxny@gmail.com>
Reviewed-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
Cc: Jiayuan Chen <jiayuan.chen@linux.dev>
---
 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..982d59cf659f5 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2716,7 +2716,7 @@ BPF_CALL_4(bpf_msg_pull_data, struct sk_msg *, msg, u32, start,
 	if (unlikely(bytes_sg_total > 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));
 	if (unlikely(!page))
 		return -ENOMEM;
-- 
2.43.0