From: John Fastabend john.fastabend@gmail.com
[ Upstream commit 81aabbb9fb7b4b1efd073b62f0505d3adad442f3 ]
In bpf_tcp_ingress we used apply_bytes to subtract bytes from sg.size which is used to track total bytes in a message. But this is not correct because apply_bytes is itself modified in the main loop doing the mem_charge.
Then at the end of this we have sg.size incorrectly set and out of sync with actual sk values. Then we can get a splat if we try to cork the data later and again try to redirect the msg to ingress. To fix instead of trying to track msg.size do the easy thing and include it as part of the sk_msg_xfer logic so that when the msg is moved the sg.size is always correct.
To reproduce the below users will need ingress + cork and hit an error path that will then try to 'free' the skmsg.
[ 173.699981] BUG: KASAN: null-ptr-deref in sk_msg_free_elem+0xdd/0x120 [ 173.699987] Read of size 8 at addr 0000000000000008 by task test_sockmap/5317
[ 173.700000] CPU: 2 PID: 5317 Comm: test_sockmap Tainted: G I 5.7.0-rc1+ #43 [ 173.700005] Hardware name: Dell Inc. Precision 5820 Tower/002KVM, BIOS 1.9.2 01/24/2019 [ 173.700009] Call Trace: [ 173.700021] dump_stack+0x8e/0xcb [ 173.700029] ? sk_msg_free_elem+0xdd/0x120 [ 173.700034] ? sk_msg_free_elem+0xdd/0x120 [ 173.700042] __kasan_report+0x102/0x15f [ 173.700052] ? sk_msg_free_elem+0xdd/0x120 [ 173.700060] kasan_report+0x32/0x50 [ 173.700070] sk_msg_free_elem+0xdd/0x120 [ 173.700080] __sk_msg_free+0x87/0x150 [ 173.700094] tcp_bpf_send_verdict+0x179/0x4f0 [ 173.700109] tcp_bpf_sendpage+0x3ce/0x5d0
Fixes: 604326b41a6fb ("bpf, sockmap: convert to generic sk_msg interface") Signed-off-by: John Fastabend john.fastabend@gmail.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Reviewed-by: Jakub Sitnicki jakub@cloudflare.com Acked-by: Martin KaFai Lau kafai@fb.com Link: https://lore.kernel.org/bpf/158861290407.14306.5327773422227552482.stgit@joh... Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/skmsg.h | 1 + net/ipv4/tcp_bpf.c | 1 - 2 files changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h index 7eb6a8754f19a..a3adbe593505d 100644 --- a/include/linux/skmsg.h +++ b/include/linux/skmsg.h @@ -186,6 +186,7 @@ static inline void sk_msg_xfer(struct sk_msg *dst, struct sk_msg *src, dst->sg.data[which] = src->sg.data[which]; dst->sg.data[which].length = size; dst->sg.size += size; + src->sg.size -= size; src->sg.data[which].length -= size; src->sg.data[which].offset += size; } diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c index 8a01428f80c1c..19bd10e6ab830 100644 --- a/net/ipv4/tcp_bpf.c +++ b/net/ipv4/tcp_bpf.c @@ -200,7 +200,6 @@ static int bpf_tcp_ingress(struct sock *sk, struct sk_psock *psock,
if (!ret) { msg->sg.start = i; - msg->sg.size -= apply_bytes; sk_psock_queue_msg(psock, tmp); sk_psock_data_ready(sk, psock); } else {