staging: lustre: mgc: fix potential use after free in error path

The config_log_add() function first calls config_log_put() with the
variable 'cld' and then jumps to label 'out_cld', which will call
the same function with the same 'cld' variable. However, at this
point, 'cld' might have been already freed by the first invocation
of config_log_put(). Even if we remove the invocation at that point,
we will still get into trouble. This is because, in the error path,
just below the label 'out_cld', we try to put 'params_cls' and
'sptlrpc_cld', which might also have been freed by config_log_put().

The point is that, config_llog_data::cld_sptlrpc and
config_llog_data::cld_params members are assigned at the beginning
of this function.

To avoid this, do not call config_log_put() inside the else block,
immediately jump to 'out_cld' instead. Moreover, remove assignments
to config_llog_data::cld_sptlrpc and config_llog_data::cld_params at
the beginning, since we already assign them below in the function
with 'cld_lock' held.

As an additional benefit, code size gets smaller.

before:
text    data     bss     dec     hex filename
26188   2256    4208   32652    7f8c drivers/staging/lustre/lustre/mgc/mgc_request.o

after:
text    data     bss     dec     hex filename
26092   2256    4208   32556    7f2c drivers/staging/lustre/lustre/mgc/mgc_request.o

Signed-off-by: Cihangir Akturk <cakturk@gmail.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lustre/mgc/mgc_request.c

@@ -288,7 +288,7 @@ config_log_add(struct obd_device *obd, char *logname,
 	struct config_llog_data *cld;
 	struct config_llog_data *sptlrpc_cld;
 	struct config_llog_data *params_cld;
-	bool locked = false;
+	struct config_llog_data *recover_cld = NULL;
 	char			seclogname[32];
 	char			*ptr;
 	int			rc;
@@ -333,20 +333,14 @@ config_log_add(struct obd_device *obd, char *logname,
 		goto out_params;
 	}
 
-	cld->cld_sptlrpc = sptlrpc_cld;
-	cld->cld_params = params_cld;
-
 	LASSERT(lsi->lsi_lmd);
 	if (!(lsi->lsi_lmd->lmd_flags & LMD_FLG_NOIR)) {
-		struct config_llog_data *recover_cld;
-
 		ptr = strrchr(seclogname, '-');
 		if (ptr) {
 			*ptr = 0;
 		} else {
 			CERROR("%s: sptlrpc log name not correct, %s: rc = %d\n",
 			       obd->obd_name, seclogname, -EINVAL);
-			config_log_put(cld);
 			rc = -EINVAL;
 			goto out_cld;
 		}
@@ -355,14 +349,10 @@ config_log_add(struct obd_device *obd, char *logname,
 			rc = PTR_ERR(recover_cld);
 			goto out_cld;
 		}
-
-		mutex_lock(&cld->cld_lock);
-		locked = true;
-		cld->cld_recover = recover_cld;
 	}
 
-	if (!locked)
-		mutex_lock(&cld->cld_lock);
+	mutex_lock(&cld->cld_lock);
+	cld->cld_recover = recover_cld;
 	cld->cld_params = params_cld;
 	cld->cld_sptlrpc = sptlrpc_cld;
 	mutex_unlock(&cld->cld_lock);