tracing/probe: Have traceprobe_parse_probe_arg() take a const arg

The two places that call traceprobe_parse_probe_arg() allocate a temporary
buffer to copy the argv[i] into, because argv[i] is constant and the
traceprobe_parse_probe_arg() will modify it to do the parsing. These two
places allocate this buffer and then free it right after calling this
function, leaving the onus of this allocation to the caller.

As there's about to be a third user of this function that will have to do
the same thing, instead of having the caller allocate the temporary
buffer, simply move that allocation into the traceprobe_parse_probe_arg()
itself, which will simplify the code of the callers.

Link: https://lkml.kernel.org/r/20210817035027.385422828@goodmis.orgAcked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_kprobe.c

@@ -873,15 +873,8 @@ static int __trace_kprobe_create(int argc, const char *argv[])
 
 	/* parse arguments */
 	for (i = 0; i < argc && i < MAX_TRACE_ARGS; i++) {
-		tmp = kstrdup(argv[i], GFP_KERNEL);
-		if (!tmp) {
-			ret = -ENOMEM;
-			goto error;
-		}
-
 		trace_probe_log_set_index(i + 2);
-		ret = traceprobe_parse_probe_arg(&tk->tp, i, tmp, flags);
-		kfree(tmp);
+		ret = traceprobe_parse_probe_arg(&tk->tp, i, argv[i], flags);
 		if (ret)
 			goto error;	/* This can be -ENOMEM */
 	}

kernel/trace/trace_probe.c

@@ -540,26 +540,34 @@ static int __parse_bitfield_probe_arg(const char *bf,
 }
 
 /* String length checking wrapper */
-static int traceprobe_parse_probe_arg_body(char *arg, ssize_t *size,
+static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
 		struct probe_arg *parg, unsigned int flags, int offset)
 {
 	struct fetch_insn *code, *scode, *tmp = NULL;
 	char *t, *t2, *t3;
+	char *arg;
 	int ret, len;
 
+	arg = kstrdup(argv, GFP_KERNEL);
+	if (!arg)
+		return -ENOMEM;
+
+	ret = -EINVAL;
 	len = strlen(arg);
 	if (len > MAX_ARGSTR_LEN) {
 		trace_probe_log_err(offset, ARG_TOO_LONG);
-		return -EINVAL;
+		goto out;
 	} else if (len == 0) {
 		trace_probe_log_err(offset, NO_ARG_BODY);
-		return -EINVAL;
+		goto out;
 	}
 
+	ret = -ENOMEM;
 	parg->comm = kstrdup(arg, GFP_KERNEL);
 	if (!parg->comm)
-		return -ENOMEM;
+		goto out;
 
+	ret = -EINVAL;
 	t = strchr(arg, ':');
 	if (t) {
 		*t = '\0';
@@ -571,22 +579,22 @@ static int traceprobe_parse_probe_arg_body(char *arg, ssize_t *size,
 				offset += t2 + strlen(t2) - arg;
 				trace_probe_log_err(offset,
 						    ARRAY_NO_CLOSE);
-				return -EINVAL;
+				goto out;
 			} else if (t3[1] != '\0') {
 				trace_probe_log_err(offset + t3 + 1 - arg,
 						    BAD_ARRAY_SUFFIX);
-				return -EINVAL;
+				goto out;
 			}
 			*t3 = '\0';
 			if (kstrtouint(t2, 0, &parg->count) || !parg->count) {
 				trace_probe_log_err(offset + t2 - arg,
 						    BAD_ARRAY_NUM);
-				return -EINVAL;
+				goto out;
 			}
 			if (parg->count > MAX_ARRAY_LEN) {
 				trace_probe_log_err(offset + t2 - arg,
 						    ARRAY_TOO_BIG);
-				return -EINVAL;
+				goto out;
 			}
 		}
 	}
@@ -598,29 +606,30 @@ static int traceprobe_parse_probe_arg_body(char *arg, ssize_t *size,
 	if (strcmp(arg, "$comm") == 0 || strncmp(arg, "\\\"", 2) == 0) {
 		/* The type of $comm must be "string", and not an array. */
 		if (parg->count || (t && strcmp(t, "string")))
-			return -EINVAL;
+			goto out;
 		parg->type = find_fetch_type("string");
 	} else
 		parg->type = find_fetch_type(t);
 	if (!parg->type) {
 		trace_probe_log_err(offset + (t ? (t - arg) : 0), BAD_TYPE);
-		return -EINVAL;
+		goto out;
 	}
 	parg->offset = *size;
 	*size += parg->type->size * (parg->count ?: 1);
 
+	ret = -ENOMEM;
 	if (parg->count) {
 		len = strlen(parg->type->fmttype) + 6;
 		parg->fmt = kmalloc(len, GFP_KERNEL);
 		if (!parg->fmt)
-			return -ENOMEM;
+			goto out;
 		snprintf(parg->fmt, len, "%s[%d]", parg->type->fmttype,
 			 parg->count);
 	}
 
 	code = tmp = kcalloc(FETCH_INSN_MAX, sizeof(*code), GFP_KERNEL);
 	if (!code)
-		return -ENOMEM;
+		goto out;
 	code[FETCH_INSN_MAX - 1].op = FETCH_OP_END;
 
 	ret = parse_probe_arg(arg, parg->type, &code, &code[FETCH_INSN_MAX - 1],
@@ -628,6 +637,7 @@ static int traceprobe_parse_probe_arg_body(char *arg, ssize_t *size,
 	if (ret)
 		goto fail;
 
+	ret = -EINVAL;
 	/* Store operation */
 	if (!strcmp(parg->type->name, "string") ||
 	    !strcmp(parg->type->name, "ustring")) {
@@ -636,7 +646,6 @@ static int traceprobe_parse_probe_arg_body(char *arg, ssize_t *size,
 		    code->op != FETCH_OP_DATA) {
 			trace_probe_log_err(offset + (t ? (t - arg) : 0),
 					    BAD_STRING);
-			ret = -EINVAL;
 			goto fail;
 		}
 		if ((code->op == FETCH_OP_IMM || code->op == FETCH_OP_COMM ||
@@ -650,7 +659,6 @@ static int traceprobe_parse_probe_arg_body(char *arg, ssize_t *size,
 			code++;
 			if (code->op != FETCH_OP_NOP) {
 				trace_probe_log_err(offset, TOO_MANY_OPS);
-				ret = -EINVAL;
 				goto fail;
 			}
 		}
@@ -672,7 +680,6 @@ static int traceprobe_parse_probe_arg_body(char *arg, ssize_t *size,
 		code++;
 		if (code->op != FETCH_OP_NOP) {
 			trace_probe_log_err(offset, TOO_MANY_OPS);
-			ret = -EINVAL;
 			goto fail;
 		}
 		code->op = FETCH_OP_ST_RAW;
@@ -687,6 +694,7 @@ static int traceprobe_parse_probe_arg_body(char *arg, ssize_t *size,
 			goto fail;
 		}
 	}
+	ret = -EINVAL;
 	/* Loop(Array) operation */
 	if (parg->count) {
 		if (scode->op != FETCH_OP_ST_MEM &&
@@ -694,13 +702,11 @@ static int traceprobe_parse_probe_arg_body(char *arg, ssize_t *size,
 		    scode->op != FETCH_OP_ST_USTRING) {
 			trace_probe_log_err(offset + (t ? (t - arg) : 0),
 					    BAD_STRING);
-			ret = -EINVAL;
 			goto fail;
 		}
 		code++;
 		if (code->op != FETCH_OP_NOP) {
 			trace_probe_log_err(offset, TOO_MANY_OPS);
-			ret = -EINVAL;
 			goto fail;
 		}
 		code->op = FETCH_OP_LP_ARRAY;
@@ -709,6 +715,7 @@ static int traceprobe_parse_probe_arg_body(char *arg, ssize_t *size,
 	code++;
 	code->op = FETCH_OP_END;
 
+	ret = 0;
 	/* Shrink down the code buffer */
 	parg->code = kcalloc(code - tmp + 1, sizeof(*code), GFP_KERNEL);
 	if (!parg->code)
@@ -724,6 +731,8 @@ static int traceprobe_parse_probe_arg_body(char *arg, ssize_t *size,
 				kfree(code->data);
 	}
 	kfree(tmp);
+out:
+	kfree(arg);
 
 	return ret;
 }
@@ -745,11 +754,11 @@ static int traceprobe_conflict_field_name(const char *name,
 	return 0;
 }
 
-int traceprobe_parse_probe_arg(struct trace_probe *tp, int i, char *arg,
+int traceprobe_parse_probe_arg(struct trace_probe *tp, int i, const char *arg,
 				unsigned int flags)
 {
 	struct probe_arg *parg = &tp->args[i];
-	char *body;
+	const char *body;
 
 	/* Increment count for freeing args in error case */
 	tp->nr_args++;

kernel/trace/trace_probe.h

@@ -354,7 +354,7 @@ int trace_probe_create(const char *raw_command, int (*createfn)(int, const char
 #define TPARG_FL_MASK	GENMASK(2, 0)
 
 extern int traceprobe_parse_probe_arg(struct trace_probe *tp, int i,
-				char *arg, unsigned int flags);
+				const char *argv, unsigned int flags);
 
 extern int traceprobe_update_arg(struct probe_arg *arg);
 extern void traceprobe_free_probe_arg(struct probe_arg *arg);

kernel/trace/trace_uprobe.c

@@ -684,16 +684,9 @@ static int __trace_uprobe_create(int argc, const char **argv)
 
 	/* parse arguments */
 	for (i = 0; i < argc && i < MAX_TRACE_ARGS; i++) {
-		tmp = kstrdup(argv[i], GFP_KERNEL);
-		if (!tmp) {
-			ret = -ENOMEM;
-			goto error;
-		}
-
 		trace_probe_log_set_index(i + 2);
-		ret = traceprobe_parse_probe_arg(&tu->tp, i, tmp,
+		ret = traceprobe_parse_probe_arg(&tu->tp, i, argv[i],
 					is_return ? TPARG_FL_RETURN : 0);
-		kfree(tmp);
 		if (ret)
 			goto error;
 	}