On 11/5/21 4:55 AM, Eric Dumazet wrote:

On 11/4/21 6:49 PM, Dmitry Safonov wrote:

quoted

static_branch_unlikely(&tcp_md5_needed) is enabled by
tcp_alloc_md5sig_pool(), so as long as the code doesn't change
tcp_md5sig_pool has been already populated if this code is being
executed.

In case tcptw->tw_md5_key allocaion failed - no reason to crash kernel:
tcp_{v4,v6}_send_ack() will send unsigned segment, the connection won't be
established, which is bad enough, but in OOM situation totally
acceptable and better than kernel crash.

Introduce tcp_md5sig_pool_ready() helper.
tcp_alloc_md5sig_pool() usage is intentionally avoided here as it's
fast-path here and it's check for sanity rather than point of actual
pool allocation. That will allow to have generic slow-path allocator
for tcp crypto pool.

Signed-off-by: Dmitry Safonov <redacted>
---
  include/net/tcp.h        | 1 +
  net/ipv4/tcp.c           | 5 +++++
  net/ipv4/tcp_minisocks.c | 5 +++--
  3 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 4da22b41bde6..3e5423a10a74 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h

@@ -1672,6 +1672,7 @@ tcp_md5_do_lookup(const struct sock *sk, int l3index,
  #endif
  
  bool tcp_alloc_md5sig_pool(void);
+bool tcp_md5sig_pool_ready(void);
  
  struct tcp_md5sig_pool *tcp_get_md5sig_pool(void);
  static inline void tcp_put_md5sig_pool(void)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index b7796b4cf0a0..c0856a6af9f5 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c

@@ -4314,6 +4314,11 @@ bool tcp_alloc_md5sig_pool(void)
  }
  EXPORT_SYMBOL(tcp_alloc_md5sig_pool);
  
+bool tcp_md5sig_pool_ready(void)
+{
+	return tcp_md5sig_pool_populated;
+}
+EXPORT_SYMBOL(tcp_md5sig_pool_ready);
  
  /**
   *	tcp_get_md5sig_pool - get md5sig_pool for this user

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index cf913a66df17..c99cdb529902 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c

@@ -293,11 +293,12 @@ void tcp_time_wait(struct sock *sk, int state, int timeo)
  			tcptw->tw_md5_key = NULL;
  			if (static_branch_unlikely(&tcp_md5_needed)) {
  				struct tcp_md5sig_key *key;
+				bool err = WARN_ON(!tcp_md5sig_pool_ready());
  
  				key = tp->af_specific->md5_lookup(sk, sk);
-				if (key) {
+				if (key && !err) {
  					tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC);
-					BUG_ON(tcptw->tw_md5_key && !tcp_alloc_md5sig_pool());
+					WARN_ON_ONCE(tcptw->tw_md5_key == NULL);
  				}
  			}
  		} while (0);

Hmmm.... how this BUG_ON() could trigger exactly ?

tcp_md5_needed can only be enabled after __tcp_alloc_md5sig_pool has succeeded.

The tcp_alloc_md5_pool here should just be removed, it no longer does 
anything since md5 pool reference counting and freeing were removed back 
in 2013 by commit 71cea17ed39f ("tcp: md5: remove spinlock usage in fast 
path").