From: Jiayuan Chen <[email protected]> Date: Fri, 12 Jun 2026 21:07:50 +0800 > From: Sechang Lim <[email protected]> > > start and len are u32, so > > u64 last = start + len; > > evaluates start + len in 32-bit and wraps before storing it in last. > The bounds check > > if (start >= offset + l || last > msg->sg.size) > return -EINVAL; > > can then be passed with an out-of-range start/len, after which the pop > loop runs off the end of the scatterlist and sk_msg_shift_left() calls > put_page() on the empty msg->sg.end slot: > > Oops: general protection fault, probably for non-canonical address > 0xdffffc0000000001: 0000 [#1] SMP KASAN PTI > KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f] > RIP: 0010:sk_msg_shift_left net/core/filter.c:2957 [inline] > RIP: 0010:____bpf_msg_pop_data net/core/filter.c:3103 [inline] > RIP: 0010:bpf_msg_pop_data+0x753/0x1a10 net/core/filter.c:2984 > Call Trace: > <TASK> > bpf_prog_4cc92c278f4d5d56+0x1b1/0x1e8 > bpf_prog_run_pin_on_cpu+0x107/0x320 include/linux/filter.h:746 > sk_psock_msg_verdict+0x357/0x7f0 net/core/skmsg.c:934 > tcp_bpf_send_verdict net/ipv4/tcp_bpf.c:420 [inline] > tcp_bpf_sendmsg+0x766/0x1ae0 net/ipv4/tcp_bpf.c:583 > __sock_sendmsg+0x153/0x1c0 net/socket.c:802 > __sys_sendto+0x326/0x430 net/socket.c:2265 > __x64_sys_sendto+0xe3/0x100 net/socket.c:2268 > do_syscall_64+0x14c/0x480 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > </TASK> > > Widen the addition with a (u64) cast so the bound is evaluated in > 64-bit and a len near U32_MAX no longer wraps below msg->sg.size. > > While here, change pop from int to u32. It counts bytes against the > unsigned scatterlist lengths and can never be negative, so the signed > type only invites sign-confusion in the pop loop. > > Fixes: 7246d8ed4dcc ("bpf: helper to pop data from messages") > Reviewed-by: Jiayuan Chen <[email protected]> > Reviewed-by: Emil Tsalapatis <[email protected]> > Signed-off-by: Sechang Lim <[email protected]> > Signed-off-by: Jiayuan Chen <[email protected]>
Reviewed-by: Kuniyuki Iwashima <[email protected]>
