From: Michal Luczaj Date: Mon, 9 Jun 2025 17:08:03 +0000 (+0200) Subject: net: Fix TOCTOU issue in sk_is_readable() X-Git-Tag: v6.12.34~62 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1e0de7582ceccbdbb227d4e0ddf65732f92526da;p=thirdparty%2Fkernel%2Fstable.git net: Fix TOCTOU issue in sk_is_readable() [ Upstream commit 2660a544fdc0940bba15f70508a46cf9a6491230 ] sk->sk_prot->sock_is_readable is a valid function pointer when sk resides in a sockmap. After the last sk_psock_put() (which usually happens when socket is removed from sockmap), sk->sk_prot gets restored and sk->sk_prot->sock_is_readable becomes NULL. This makes sk_is_readable() racy, if the value of sk->sk_prot is reloaded after the initial check. Which in turn may lead to a null pointer dereference. Ensure the function pointer does not turn NULL after the check. Fixes: 8934ce2fd081 ("bpf: sockmap redirect ingress support") Suggested-by: Jakub Sitnicki Signed-off-by: Michal Luczaj Reviewed-by: Willem de Bruijn Link: https://patch.msgid.link/20250609-skisreadable-toctou-v1-1-d0dfb2d62c37@rbox.co Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- diff --git a/include/net/sock.h b/include/net/sock.h index fa9b9dadbe170..b7270b6b9e9cc 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -2942,8 +2942,11 @@ int sock_ioctl_inout(struct sock *sk, unsigned int cmd, int sk_ioctl(struct sock *sk, unsigned int cmd, void __user *arg); static inline bool sk_is_readable(struct sock *sk) { - if (sk->sk_prot->sock_is_readable) - return sk->sk_prot->sock_is_readable(sk); + const struct proto *prot = READ_ONCE(sk->sk_prot); + + if (prot->sock_is_readable) + return prot->sock_is_readable(sk); + return false; } #endif /* _SOCK_H */