setexpr: Split the core logic into its own function

At present this function always allocates a large amount of stack, and
selects its own size for buffers. This makes it hard to test the code
for buffer overflow.

Separate out the inner logic of the substitution so that tests can call
this directly. This will allow checking that the algorithm does not
overflow the buffer.

Fix up one of the error lines at the same time, since it should be
printing nbuf_size, not data_size.

Signed-off-by: Simon Glass <sjg@chromium.org>

1 files changed, 98 insertions, 58 deletions

diff --git a/cmd/setexpr.c b/cmd/setexpr.c
index dd9c2574fd..fe3435b4d9 100644
--- a/cmd/setexpr.c
+++ b/cmd/setexpr.c
@@ -58,9 +58,6 @@ static ulong get_arg(char *s, int w)
 
 #include <slre.h>
 
-#define SLRE_BUFSZ	16384
-#define SLRE_PATSZ	4096
-
 /*
  * memstr - Find the first substring in memory
  * @s1: The string to be searched
@@ -83,13 +80,24 @@ static char *memstr(const char *s1, int l1, const char *s2, int l2)
 	return NULL;
 }
 
-static char *substitute(char *string,	/* string buffer */
-			int *slen,	/* current string length */
-			int ssize,	/* string bufer size */
-			const char *old,/* old (replaced) string */
-			int olen,	/* length of old string */
-			const char *new,/* new (replacement) string */
-			int nlen)	/* length of new string */
+/**
+ * substitute() - Substitute part of one string with another
+ *
+ * This updates @string so that the first occurrence of @old is replaced with
+ * @new
+ *
+ * @string: String buffer containing string to update at the start
+ * @slen: Pointer to current string length, updated on success
+ * @ssize: Size of string buffer
+ * @old: Old string to find in the buffer (no terminator needed)
+ * @olen: Length of @old excluding terminator
+ * @new: New string to replace @old with
+ * @nlen: Length of @new excluding terminator
+ * @return pointer to immediately after the copied @new in @string, or NULL if
+ *	no replacement took place
+ */
+static char *substitute(char *string, int *slen, int ssize,
+			const char *old, int olen, const char *new, int nlen)
 {
 	char *p = memstr(string, *slen, old, olen);
 
@@ -118,7 +126,7 @@ static char *substitute(char *string,	/* string buffer */
 		memmove(p + nlen, p + olen, tail);
 	}
 
-	/* insert substitue */
+	/* insert substitute */
 	memcpy(p, new, nlen);
 
 	*slen += nlen - olen;
@@ -126,52 +134,33 @@ static char *substitute(char *string,	/* string buffer */
 	return p + nlen;
 }
 
-/*
- * Perform regex operations on a environment variable
+/**
+ * regex_sub() - Replace a regex pattern with a string
  *
- * Returns 0 if OK, 1 in case of errors.
+ * @data: Buffer containing the string to update
+ * @data_size: Size of buffer (must be large enough for the new string)
+ * @nbuf: Back-reference buffer
+ * @nbuf_size: Size of back-reference buffer (must be larger enough for @s plus
+ *	all back-reference expansions)
+ * @r: Regular expression to find
+ * @s: String to replace with
+ * @global: true to replace all matches in @data, false to replace just the
+ *	first
+ * @return 0 if OK, 1 on error
  */
-static int regex_sub(const char *name,
-	const char *r, const char *s, const char *t,
-	int global)
+static int regex_sub(char *data, uint data_size, char *nbuf, uint nbuf_size,
+		     const char *r, const char *s, bool global)
 {
 	struct slre slre;
-	char data[SLRE_BUFSZ];
 	char *datap = data;
-	const char *value;
 	int res, len, nlen, loop;
 
-	if (name == NULL)
-		return 1;
-
 	if (slre_compile(&slre, r) == 0) {
 		printf("Error compiling regex: %s\n", slre.err_str);
 		return 1;
 	}
 
-	if (t == NULL) {
-		value = env_get(name);
-
-		if (value == NULL) {
-			printf("## Error: variable \"%s\" not defined\n", name);
-			return 1;
-		}
-		t = value;
-	}
-
-	debug("REGEX on %s=%s\n", name, t);
-	debug("REGEX=\"%s\", SUBST=\"%s\", GLOBAL=%d\n",
-		r, s ? s : "<NULL>", global);
-
-	len = strlen(t);
-	if (len + 1 > SLRE_BUFSZ) {
-		printf("## error: subst buffer overflow: have %d, need %d\n",
-			SLRE_BUFSZ, len + 1);
-		return 1;
-	}
-
-	strcpy(data, t);
-
+	len = strlen(data);
 	if (s == NULL)
 		nlen = 0;
 	else
@@ -179,7 +168,6 @@ static int regex_sub(const char *name,
 
 	for (loop = 0;; loop++) {
 		struct cap caps[slre.num_caps + 2];
-		char nbuf[SLRE_PATSZ];
 		const char *old;
 		char *np;
 		int i, olen;
@@ -199,7 +187,7 @@ static int regex_sub(const char *name,
 
 		if (res == 0) {
 			if (loop == 0) {
-				printf("%s: No match\n", t);
+				printf("%s: No match\n", data);
 				return 1;
 			} else {
 				break;
@@ -208,17 +196,15 @@ static int regex_sub(const char *name,
 
 		debug("## MATCH ## %s\n", data);
 
-		if (s == NULL) {
-			printf("%s=%s\n", name, t);
+		if (!s)
 			return 1;
-		}
 
 		old = caps[0].ptr;
 		olen = caps[0].len;
 
-		if (nlen + 1 >= SLRE_PATSZ) {
+		if (nlen + 1 >= nbuf_size) {
 			printf("## error: pattern buffer overflow: have %d, need %d\n",
-				SLRE_BUFSZ, nlen + 1);
+			       nbuf_size, nlen + 1);
 			return 1;
 		}
 		strcpy(nbuf, s);
@@ -263,7 +249,7 @@ static int regex_sub(const char *name,
 					break;
 
 				np = substitute(np, &nlen,
-					SLRE_PATSZ,
+					nbuf_size,
 					backref, 2,
 					caps[i].ptr, caps[i].len);
 
@@ -273,9 +259,8 @@ static int regex_sub(const char *name,
 		}
 		debug("## SUBST(2) ## %s\n", nbuf);
 
-		datap = substitute(datap, &len, SLRE_BUFSZ,
-				old, olen,
-				nbuf, nlen);
+		datap = substitute(datap, &len, data_size, old, olen,
+				   nbuf, nlen);
 
 		if (datap == NULL)
 			return 1;
@@ -289,6 +274,61 @@ static int regex_sub(const char *name,
 	}
 	debug("## FINAL (now env_set()) :  %s\n", data);
 
+	return 0;
+}
+
+#define SLRE_BUFSZ	16384
+#define SLRE_PATSZ	4096
+
+/*
+ * Perform regex operations on a environment variable
+ *
+ * Returns 0 if OK, 1 in case of errors.
+ */
+static int regex_sub_var(const char *name, const char *r, const char *s,
+			 const char *t, int global)
+{
+	struct slre slre;
+	char data[SLRE_BUFSZ];
+	char nbuf[SLRE_PATSZ];
+	const char *value;
+	int len;
+	int ret;
+
+	if (!name)
+		return 1;
+
+	if (slre_compile(&slre, r) == 0) {
+		printf("Error compiling regex: %s\n", slre.err_str);
+		return 1;
+	}
+
+	if (!t) {
+		value = env_get(name);
+		if (!value) {
+			printf("## Error: variable \"%s\" not defined\n", name);
+			return 1;
+		}
+		t = value;
+	}
+
+	debug("REGEX on %s=%s\n", name, t);
+	debug("REGEX=\"%s\", SUBST=\"%s\", GLOBAL=%d\n", r, s ? s : "<NULL>",
+	      global);
+
+	len = strlen(t);
+	if (len + 1 > SLRE_BUFSZ) {
+		printf("## error: subst buffer overflow: have %d, need %d\n",
+		       SLRE_BUFSZ, len + 1);
+		return 1;
+	}
+
+	strcpy(data, t);
+
+	ret = regex_sub(data, SLRE_BUFSZ, nbuf, SLRE_PATSZ, r, s, global);
+	if (ret)
+		return 1;
+
 	printf("%s=%s\n", name, data);
 
 	return env_set(name, data);
@@ -331,10 +371,10 @@ static int do_setexpr(struct cmd_tbl *cmdtp, int flag, int argc,
 	 * with 5 args, "t" will be NULL
 	 */
 	if (strcmp(argv[2], "gsub") == 0)
-		return regex_sub(argv[1], argv[3], argv[4], argv[5], 1);
+		return regex_sub_var(argv[1], argv[3], argv[4], argv[5], 1);
 
 	if (strcmp(argv[2], "sub") == 0)
-		return regex_sub(argv[1], argv[3], argv[4], argv[5], 0);
+		return regex_sub_var(argv[1], argv[3], argv[4], argv[5], 0);
 #endif
 
 	/* standard operators: "setexpr name val1 op val2" */