From a652a4bc21695a57c3b8d13d222a6f8b41f100aa Mon Sep 17 00:00:00 2001 From: Trond Myklebust Date: Mon, 12 Nov 2018 15:30:52 -0500 Subject: [PATCH] SUNRPC: Fix a Oops when destroying the RPCSEC_GSS credential cache Commit 07d02a67b7fa causes a use-after free in the RPCSEC_GSS credential destroy code, because the call to get_rpccred() in gss_destroying_context() will now always fail to increment the refcount. While we could just replace the get_rpccred() with a refcount_set(), that would have the unfortunate consequence of resurrecting a credential in the credential cache for which we are in the process of destroying the RPCSEC_GSS context. Rather than do this, we choose to make a copy that is never added to the cache and use that to destroy the context. Fixes: 07d02a67b7fa ("SUNRPC: Simplify lookup code") Signed-off-by: Trond Myklebust --- net/sunrpc/auth_gss/auth_gss.c | 61 +++++++++++++++++++++++----------- 1 file changed, 42 insertions(+), 19 deletions(-) diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c index 30f970cdc7f6..5d3f252659f1 100644 --- a/net/sunrpc/auth_gss/auth_gss.c +++ b/net/sunrpc/auth_gss/auth_gss.c @@ -1239,36 +1239,59 @@ gss_create(const struct rpc_auth_create_args *args, struct rpc_clnt *clnt) return &gss_auth->rpc_auth; } +static struct gss_cred * +gss_dup_cred(struct gss_auth *gss_auth, struct gss_cred *gss_cred) +{ + struct gss_cred *new; + + /* Make a copy of the cred so that we can reference count it */ + new = kzalloc(sizeof(*gss_cred), GFP_NOIO); + if (new) { + struct auth_cred acred = { + .uid = gss_cred->gc_base.cr_uid, + }; + struct gss_cl_ctx *ctx = + rcu_dereference_protected(gss_cred->gc_ctx, 1); + + rpcauth_init_cred(&new->gc_base, &acred, + &gss_auth->rpc_auth, + &gss_nullops); + new->gc_base.cr_flags = 1UL << RPCAUTH_CRED_UPTODATE; + new->gc_service = gss_cred->gc_service; + new->gc_principal = gss_cred->gc_principal; + kref_get(&gss_auth->kref); + rcu_assign_pointer(new->gc_ctx, ctx); + gss_get_ctx(ctx); + } + return new; +} + /* - * gss_destroying_context will cause the RPCSEC_GSS to send a NULL RPC call + * gss_send_destroy_context will cause the RPCSEC_GSS to send a NULL RPC call * to the server with the GSS control procedure field set to * RPC_GSS_PROC_DESTROY. This should normally cause the server to release * all RPCSEC_GSS state associated with that context. */ -static int -gss_destroying_context(struct rpc_cred *cred) +static void +gss_send_destroy_context(struct rpc_cred *cred) { struct gss_cred *gss_cred = container_of(cred, struct gss_cred, gc_base); struct gss_auth *gss_auth = container_of(cred->cr_auth, struct gss_auth, rpc_auth); struct gss_cl_ctx *ctx = rcu_dereference_protected(gss_cred->gc_ctx, 1); + struct gss_cred *new; struct rpc_task *task; - if (test_bit(RPCAUTH_CRED_UPTODATE, &cred->cr_flags) == 0) - return 0; + new = gss_dup_cred(gss_auth, gss_cred); + if (new) { + ctx->gc_proc = RPC_GSS_PROC_DESTROY; - ctx->gc_proc = RPC_GSS_PROC_DESTROY; - cred->cr_ops = &gss_nullops; + task = rpc_call_null(gss_auth->client, &new->gc_base, + RPC_TASK_ASYNC|RPC_TASK_SOFT); + if (!IS_ERR(task)) + rpc_put_task(task); - /* Take a reference to ensure the cred will be destroyed either - * by the RPC call or by the put_rpccred() below */ - get_rpccred(cred); - - task = rpc_call_null(gss_auth->client, cred, RPC_TASK_ASYNC|RPC_TASK_SOFT); - if (!IS_ERR(task)) - rpc_put_task(task); - - put_rpccred(cred); - return 1; + put_rpccred(&new->gc_base); + } } /* gss_destroy_cred (and gss_free_ctx) are used to clean up after failure @@ -1330,8 +1353,8 @@ static void gss_destroy_cred(struct rpc_cred *cred) { - if (gss_destroying_context(cred)) - return; + if (test_and_clear_bit(RPCAUTH_CRED_UPTODATE, &cred->cr_flags) != 0) + gss_send_destroy_context(cred); gss_destroy_nullcred(cred); }