From: Weiming Shi <[email protected]> When the scatterlist ring is full or nearly full, bpf_msg_push_data() enters a copy fallback path and computes copy + len for the page allocation size. Since len comes from BPF with arg3_type = ARG_ANYTHING and both are u32, a crafted len can wrap the sum to a small value, causing an undersized allocation followed by an out-of-bounds memcpy.
BUG: unable to handle page fault for address: ffffed104089a402 Oops: Oops: 0000 [#1] SMP KASAN NOPTI Call Trace: __asan_memcpy (mm/kasan/shadow.c:105) bpf_msg_push_data (net/core/filter.c:2852 net/core/filter.c:2788) bpf_prog_9ed8b5711920a7d7+0x2e/0x36 sk_psock_msg_verdict (net/core/skmsg.c:934) tcp_bpf_sendmsg (net/ipv4/tcp_bpf.c:421 net/ipv4/tcp_bpf.c:584) __sys_sendto (net/socket.c:2206) do_syscall_64 (arch/x86/entry/syscall_64.c:94) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130) Add an overflow check before the allocation. 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]> --- To sashiko: Regarding bpf_msg_push_data() reading "copy = msg->sg.data[i].length" with i == msg->sg.end (appending at the very end of a full/near-full ring): This is pre-existing code, not touched by this series, and reproducing it needs a narrow combination -- a pure append at the end so the loop exits with i == msg->sg.end, a full/near-full ring, plus a prior push/pop history that leaves a stale length in the otherwise-unused end slot. A freshly built ring zeroes that slot, so copy stays 0. We don't consider it practically reproducible. Even then it's already covered: the overflow check in patch 1 ("copy + len < copy") rejects the dangerous case, and __GFP_ZERO in patch 3 prevents any data exposure. Not worth fixing here. --- net/core/filter.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/net/core/filter.c b/net/core/filter.c index 9590877b0714f..3c8f1cedb217f 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -2829,6 +2829,9 @@ BPF_CALL_4(bpf_msg_push_data, struct sk_msg *, msg, u32, start, if (!space || (space == 1 && start != offset)) copy = msg->sg.data[i].length; + if (unlikely(copy + len < copy)) + return -EINVAL; + page = alloc_pages(__GFP_NOWARN | GFP_ATOMIC | __GFP_COMP, get_order(copy + len)); if (unlikely(!page)) -- 2.43.0
