[PATCH] chcr_ktls: fix a possible null-pointer dereference in chcr_ktls_dev_add()

[Tuo Li <islituo@gmail.com>]

There is a possible null-pointer dereference related to the wait-completion
synchronization mechanism in the function chcr_ktls_dev_add().

Consider the following execution scenario:

  chcr_ktls_cpl_act_open_rpl()   //641
    u_ctx = adap->uld[CXGB4_ULD_KTLS].handle;   //686
    if (u_ctx) {  //687
    complete(&tx_info->completion);  //704

The variable u_ctx is checked by an if statement at Line 687, which means
it can be NULL. Then, complete() is called at Line 704, which will wake
up wait_for_completion_xxx().

Consider the wait_for_completion_timeout() in chcr_ktls_dev_add():

  chcr_ktls_dev_add()  //412
    u_ctx = adap->uld[CXGB4_ULD_KTLS].handle;  //432
    wait_for_completion_timeout(&tx_info->completion, 30 * HZ); //551
    xa_erase(&u_ctx->tid_list, tx_info->tid);  //580

The variable u_ctx is dereferenced without being rechecked at Line 580
after the wait_for_completion_timeout(), which can introduce a null-pointer
dereference. Besides, the variable u_ctx is also checked at Line 442 in
chcr_ktls_dev_add(), which indicates that u_ctx is likely to be NULL in
some execution contexts.

To fix this possible null-pointer dereference, a NULL check is put ahead of
the call to xa_erase().

This potential bug was discovered using an experimental static analysis
tool developed by our team. The tool deduces complete() and
wait_for_completion() pairs using alias analysis. It then applies data
flow analysis to detect null-pointer dereferences across synchronization
points.

Fixes: 65e302a9bd57 ("cxgb4/ch_ktls: Clear resources when pf4 device is removed") 
Signed-off-by: Tuo Li <islituo@gmail.com>
---
 drivers/net/ethernet/chelsio/inline_crypto/ch_ktls/chcr_ktls.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/chelsio/inline_crypto/ch_ktls/chcr_ktls.c b/drivers/net/ethernet/chelsio/inline_crypto/ch_ktls/chcr_ktls.c
index e8e460a92e0e..524c8e032bc8 100644
--- a/drivers/net/ethernet/chelsio/inline_crypto/ch_ktls/chcr_ktls.c
+++ b/drivers/net/ethernet/chelsio/inline_crypto/ch_ktls/chcr_ktls.c
@@ -577,7 +577,8 @@ static int chcr_ktls_dev_add(struct net_device *netdev, struct sock *sk,
 	cxgb4_remove_tid(&tx_info->adap->tids, tx_info->tx_chan,
 			 tx_info->tid, tx_info->ip_family);
 
-	xa_erase(&u_ctx->tid_list, tx_info->tid);
+	if (u_ctx)
+		xa_erase(&u_ctx->tid_list, tx_info->tid);
 
 put_module:
 	/* release module refcount */
-- 
2.43.0