> On Dec 12, 2022, at 01:03, minoura <minoura@xxxxxxxxxxxxx> wrote:
>
> From: minoura makoto <minoura@xxxxxxxxxxxxx>
>
> Commit 9130b8dbc6ac ("SUNRPC: allow for upcalls for the same uid
> but different gss service") introduced `auth` argument to
> __gss_find_upcall(), but in gss_pipe_downcall() it was left as NULL
> since it (and auth->service) was not (yet) determined.
>
> When multiple upcalls with the same uid and different service are
> ongoing, it could happen that __gss_find_upcall(), which returns the
> first match found in the pipe->in_downcall list, could not find the
> correct gss_msg corresponding to the downcall we are looking for.
> Moreover, it might return a msg which is not sent to rpc.gssd yet.
>
> We could see mount.nfs process hung in D state with multiple mount.nfs
> are executed in parallel. The call trace below is of CentOS 7.9
> kernel-3.10.0-1160.24.1.el7.x86_64 but we observed the same hang w/
> elrepo kernel-ml-6.0.7-1.el7.
>
> PID: 71258 TASK: ffff91ebd4be0000 CPU: 36 COMMAND: "mount.nfs"
> #0 [ffff9203ca3234f8] __schedule at ffffffffa3b8899f
> #1 [ffff9203ca323580] schedule at ffffffffa3b88eb9
> #2 [ffff9203ca323590] gss_cred_init at ffffffffc0355818 [auth_rpcgss]
> #3 [ffff9203ca323658] rpcauth_lookup_credcache at ffffffffc0421ebc [sunrpc]
> #4 [ffff9203ca3236d8] gss_lookup_cred at ffffffffc0353633 [auth_rpcgss]
> #5 [ffff9203ca3236e8] rpcauth_lookupcred at ffffffffc0421581 [sunrpc]
> #6 [ffff9203ca323740] rpcauth_refreshcred at ffffffffc04223d3 [sunrpc]
> #7 [ffff9203ca3237a0] call_refresh at ffffffffc04103dc [sunrpc]
> #8 [ffff9203ca3237b8] __rpc_execute at ffffffffc041e1c9 [sunrpc]
> #9 [ffff9203ca323820] rpc_execute at ffffffffc0420a48 [sunrpc]
>
> The scenario is like this. Let's say there are two upcalls for
> services A and B, A -> B in pipe->in_downcall, B -> A in pipe->pipe.
>
> When rpc.gssd reads pipe to get the upcall msg corresponding to
> service B from pipe->pipe and then writes the response, in
> gss_pipe_downcall the msg corresponding to service A will be picked
> because only uid is used to find the msg and it is before the one for
> B in pipe->in_downcall. And the process waiting for the msg
> corresponding to service A will be woken up.
>
> Actual scheduing of that process might be after rpc.gssd processes the
> next msg. In rpc_pipe_generic_upcall it clears msg->errno (for A).
> The process is scheduled to see gss_msg->ctx == NULL and
> gss_msg->msg.errno == 0, therefore it cannot break the loop in
> gss_create_upcall and is never woken up after that.
>
> This patch adds a simple check to ensure that a msg which is not
> sent to rpc.gssd yet is not chosen as the matching upcall upon
> receiving a downcall.
>
> Fixes: Commit 9130b8dbc6ac ("SUNRPC: allow for upcalls for the same uid but different gss service")
> Signed-off-by: minoura makoto <minoura@xxxxxxxxxxxxx>
> Signed-off-by: Hiroshi Shimamoto <h-shimamoto@xxxxxxx>
> Tested-by: Hiroshi Shimamoto <h-shimamoto@xxxxxxx>
> Cc: Trond Myklebust <trondmy@xxxxxxxxxxxxxxx>
> ---
> v2: use gss_release_msg instead of refcount_dec in fatal_signal_pending case
> v3: just ensure the msg is already sent instead of serialization (based on Trond's advice)
> ---
> include/linux/sunrpc/rpc_pipe_fs.h | 5 +++++
> net/sunrpc/auth_gss/auth_gss.c | 19 +++++++++++++++++--
> 2 files changed, 22 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/sunrpc/rpc_pipe_fs.h b/include/linux/sunrpc/rpc_pipe_fs.h
> index cd188a527d16..6a29682cb857 100644
> --- a/include/linux/sunrpc/rpc_pipe_fs.h
> +++ b/include/linux/sunrpc/rpc_pipe_fs.h
> @@ -92,6 +92,11 @@ extern ssize_t rpc_pipe_generic_upcall(struct file *, struct rpc_pipe_msg *,
> char __user *, size_t);
> extern int rpc_queue_upcall(struct rpc_pipe *, struct rpc_pipe_msg *);
>
> +/* returns true if the msg is in-flight, i.e., already eaten by the peer */
> +static inline bool rpc_msg_is_inflight(struct rpc_pipe_msg *msg) {
Nit: please make that a ‘const struct rpc_pipe_msg *’ argument.
> + return (msg->copied != 0 && list_empty(&msg->list));
> +}
> +
> struct rpc_clnt;
> extern struct dentry *rpc_create_client_dir(struct dentry *, const char *, struct rpc_clnt *);
> extern int rpc_remove_client_dir(struct rpc_clnt *);
> diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c
> index 7bb247c51e2f..51b67ebe09bf 100644
> --- a/net/sunrpc/auth_gss/auth_gss.c
> +++ b/net/sunrpc/auth_gss/auth_gss.c
> @@ -302,7 +302,7 @@ __gss_find_upcall(struct rpc_pipe *pipe, kuid_t uid, const struct gss_auth *auth
> list_for_each_entry(pos, &pipe->in_downcall, list) {
> if (!uid_eq(pos->uid, uid))
> continue;
> - if (auth && pos->auth->service != auth->service)
> + if (pos->auth->service != auth->service)
> continue;
> refcount_inc(&pos->count);
> return pos;
> @@ -686,6 +686,21 @@ gss_create_upcall(struct gss_auth *gss_auth, struct gss_cred *gss_cred)
> return err;
> }
>
> +static struct gss_upcall_msg *
> +gss_find_matching_upcall(struct rpc_pipe *pipe, kuid_t uid)
Could we please call this ‘gss_find_downcall()’ in order to clarify the use case?
> +{
> + struct gss_upcall_msg *pos;
> + list_for_each_entry(pos, &pipe->in_downcall, list) {
> + if (!uid_eq(pos->uid, uid))
> + continue;
> + if (!rpc_msg_is_inflight(&pos->msg))
> + continue;
> + refcount_inc(&pos->count);
> + return pos;
> + }
> + return NULL;
> +}
> +
> #define MSG_BUF_MAXSIZE 1024
>
> static ssize_t
> @@ -732,7 +747,7 @@ gss_pipe_downcall(struct file *filp, const char __user *src, size_t mlen)
> err = -ENOENT;
> /* Find a matching upcall */
> spin_lock(&pipe->lock);
> - gss_msg = __gss_find_upcall(pipe, uid, NULL);
> + gss_msg = gss_find_matching_upcall(pipe, uid);
> if (gss_msg == NULL) {
> spin_unlock(&pipe->lock);
> goto err_put_ctx;
> --
> 2.25.1
>
Otherwise, this looks great.
_________________________________
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@xxxxxxxxxxxxxxx
