Re: [PATCH bpf 1/2] bpf, sockmap: Don't leak UDP socks on lookup-bind-release
From: Jiayuan Chen <jiayuan.chen@linux.dev>
Date: 2026-06-24 01:36:31
Also in:
bpf, linux-kselftest, lkml
On 6/24/26 2:03 AM, Michal Luczaj wrote:
UDP sockets get SOCK_RCU_FREE set when (auto-)bound. This means
sk_is_refcounted(unbound) = true, while sk_is_refcounted(bound) = false.
Because sockmap accepts unbound UDP sockets, a BPF program can increment a
socket's refcount via lookup. If the socket is subsequently bound, the
transition from unbound to bound causes bpf_sk_release() to skip the
decrement of the refcount, causing a memory leak.
unreferenced object 0xffff88810bc2eb40 (size 1984):
comm "test_progs", pid 2451, jiffies 4295320596
hex dump (first 32 bytes):
7f 00 00 01 7f 00 00 01 d2 04 1b b7 04 d2 00 00 ................
02 00 01 40 00 00 00 00 00 00 00 00 00 00 00 00 ...@............
backtrace (crc bdee079d):
kmem_cache_alloc_noprof+0x557/0x660
sk_prot_alloc+0x69/0x240
sk_alloc+0x30/0x460
inet_create+0x2ce/0xf80
__sock_create+0x25b/0x5c0
__sys_socket+0x119/0x1d0
__x64_sys_socket+0x72/0xd0
do_syscall_64+0xa1/0x5f0
entry_SYSCALL_64_after_hwframe+0x76/0x7e
Maintain balanced refcounts across sk lookup/release: (re-)set
SOCK_RCU_FREE on proto update to treat the socket (whether bound or
unbound) as not requiring a refcount increment on (a RCU protected) lookup.
Fixes: 0c48eefae712 ("sock_map: Lift socket state restriction for datagram sockets")
Signed-off-by: Michal Luczaj <redacted>Reviewed-by: Jiayuan Chen <jiayuan.chen@linux.dev>