Re: [PATCH] iscsi: iscsi_tcp: Avoid holding spinlock while calling getpeername

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On 9/27/20 11:33 PM, Mark Mielke wrote:
> Kernel may fail to boot or devices may fail to come up when
> initializing iscsi_tcp devices starting with Linux 5.8.
> 
> Marc Dionne identified the cause in RHBZ#1877345.
> 
> Commit a79af8a64d39 ("[SCSI] iscsi_tcp: use iscsi_conn_get_addr_param
> libiscsi function") introduced getpeername() within the session spinlock.
> 
> Commit 1b66d253610c ("bpf: Add get{peer, sock}name attach types for
> sock_addr") introduced BPF_CGROUP_RUN_SA_PROG_LOCK() within getpeername,
> which acquires a mutex and when used from iscsi_tcp devices can now lead
> to "BUG: scheduling while atomic:" and subsequent damage.
> 
> This commit ensures that the spinlock is released before calling
> getpeername() or getsockname(). sock_hold() and sock_put() are
> used to ensure that the socket reference is preserved until after
> the getpeername() or getsockname() complete.
> 
> Reported-by: Marc Dionne <marc.c.dionne@xxxxxxxxx>
> Link: https://urldefense.com/v3/__https://bugzilla.redhat.com/show_bug.cgi?id=1877345__;!!GqivPVa7Brio!IykqCqCEtE_EyrhXerYzj_cIlmkenkaAVddyoEOw9T6n4nExSaGFHkn0ZQrLBVSUtxQ_$ 
> Link: https://urldefense.com/v3/__https://lkml.org/lkml/2020/7/28/1085__;!!GqivPVa7Brio!IykqCqCEtE_EyrhXerYzj_cIlmkenkaAVddyoEOw9T6n4nExSaGFHkn0ZQrLBRT9NL69$ 
> Link: https://urldefense.com/v3/__https://lkml.org/lkml/2020/8/31/459__;!!GqivPVa7Brio!IykqCqCEtE_EyrhXerYzj_cIlmkenkaAVddyoEOw9T6n4nExSaGFHkn0ZQrLBfxZYLKs$ 
> Fixes: a79af8a64d39 ("[SCSI] iscsi_tcp: use iscsi_conn_get_addr_param libiscsi function")
> Fixes: 1b66d253610c ("bpf: Add get{peer, sock}name attach types for sock_addr")
> Signed-off-by: Mark Mielke <mark.mielke@xxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> ---
>  drivers/scsi/iscsi_tcp.c | 22 +++++++++++++++-------
>  1 file changed, 15 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/scsi/iscsi_tcp.c b/drivers/scsi/iscsi_tcp.c
> index b5dd1caae5e9..d10efb66cf19 100644
> --- a/drivers/scsi/iscsi_tcp.c
> +++ b/drivers/scsi/iscsi_tcp.c
> @@ -736,6 +736,7 @@ static int iscsi_sw_tcp_conn_get_param(struct iscsi_cls_conn *cls_conn,
>  	struct iscsi_tcp_conn *tcp_conn = conn->dd_data;
>  	struct iscsi_sw_tcp_conn *tcp_sw_conn = tcp_conn->dd_data;
>  	struct sockaddr_in6 addr;
> +	struct socket *sock;
>  	int rc;
>  
>  	switch(param) {
> @@ -747,13 +748,17 @@ static int iscsi_sw_tcp_conn_get_param(struct iscsi_cls_conn *cls_conn,
>  			spin_unlock_bh(&conn->session->frwd_lock);
>  			return -ENOTCONN;
>  		}
> +		sock = tcp_sw_conn->sock;
> +		sock_hold(sock->sk);
> +		spin_unlock_bh(&conn->session->frwd_lock);
> +
>  		if (param == ISCSI_PARAM_LOCAL_PORT)
> -			rc = kernel_getsockname(tcp_sw_conn->sock,
> +			rc = kernel_getsockname(sock,
>  						(struct sockaddr *)&addr);
>  		else
> -			rc = kernel_getpeername(tcp_sw_conn->sock,
> +			rc = kernel_getpeername(sock,
>  						(struct sockaddr *)&addr);
> -		spin_unlock_bh(&conn->session->frwd_lock);
> +		sock_put(sock->sk);
>  		if (rc < 0)
>  			return rc;
>  
> @@ -775,6 +780,7 @@ static int iscsi_sw_tcp_host_get_param(struct Scsi_Host *shost,
>  	struct iscsi_tcp_conn *tcp_conn;
>  	struct iscsi_sw_tcp_conn *tcp_sw_conn;
>  	struct sockaddr_in6 addr;
> +	struct socket *sock;
>  	int rc;
>  
>  	switch (param) {
> @@ -789,16 +795,18 @@ static int iscsi_sw_tcp_host_get_param(struct Scsi_Host *shost,
>  			return -ENOTCONN;
>  		}
>  		tcp_conn = conn->dd_data;
> -
>  		tcp_sw_conn = tcp_conn->dd_data;
> -		if (!tcp_sw_conn->sock) {
> +		sock = tcp_sw_conn->sock;
> +		if (!sock) {
>  			spin_unlock_bh(&session->frwd_lock);
>  			return -ENOTCONN;
>  		}
> +		sock_hold(sock->sk);
> +		spin_unlock_bh(&session->frwd_lock);
>  
> -		rc = kernel_getsockname(tcp_sw_conn->sock,
> +		rc = kernel_getsockname(sock,
>  					(struct sockaddr *)&addr);
> -		spin_unlock_bh(&session->frwd_lock);
> +		sock_put(sock->sk);
>  		if (rc < 0)
>  			return rc;
>  
> 

Reviewed-by: Mike Christie <michael.christie@xxxxxxxxxx>



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