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net: Fix TOCTOU issue in sk_is_readable()

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[ Upstream commit 2660a544fd ]

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: 8934ce2fd0 ("bpf: sockmap redirect ingress support")
Suggested-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Michal Luczaj <mhal@rbox.co>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20250609-skisreadable-toctou-v1-1-d0dfb2d62c37@rbox.co
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Michal Luczaj
2025-06-09 19:08:03 +02:00
committed by Greg Kroah-Hartman
parent c6dad167aa
commit ff55c85a92
1 changed files with 5 additions and 2 deletions
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include/net/sock.h
+5 -2
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@@ -3043,8 +3043,11 @@ 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 */