klibc - Mar 2020 - [klibc:update-dash] dash: exec: Do not allocate stack string in padvance

Commit-ID:  6e48f19172d90268f524bf1a3788f7c023b24391
Gitweb:    
http://git.kernel.org/?p=libs/klibc/klibc.git;a=commit;h=6e48f19172d90268f524bf1a3788f7c023b24391
Author:     Herbert Xu <herbert at gondor.apana.org.au>
AuthorDate: Sat, 19 May 2018 02:39:48 +0800
Committer:  Ben Hutchings <ben at decadent.org.uk>
CommitDate: Sat, 28 Mar 2020 21:42:55 +0000

[klibc] dash: exec: Do not allocate stack string in padvance

[ dash commit 4f7527f8e49276894751a9b100e68bc46568bb85 ]

Many callers of padvance immediately free the allocated string
so this patch moves the stalloc call to the caller.  Instead of
returning the allocated string, padvance now returns the length
to allocate (this may be longer than the actual string length,
even including the NUL).  For the case where we would previously
return NULL, we now return -1.

Signed-off-by: Herbert Xu <herbert at gondor.apana.org.au>
Signed-off-by: Ben Hutchings <ben at decadent.org.uk>

---
 usr/dash/cd.c   |  8 +++++---
 usr/dash/exec.c | 26 +++++++++++++-------------
 usr/dash/exec.h |  2 +-
 usr/dash/mail.c |  7 +++++--
 usr/dash/main.c | 12 +++++-------
 5 files changed, 29 insertions(+), 26 deletions(-)

diff --git a/usr/dash/cd.c b/usr/dash/cd.c
index a4e024d8..610a4fa8 100644
--- a/usr/dash/cd.c
+++ b/usr/dash/cd.c
@@ -98,6 +98,7 @@ cdcmd(int argc, char **argv)
 	char c;
 	struct stat statb;
 	int flags;
+	int len;
 
 	flags = cdopt();
 	dest = *argptr;
@@ -127,9 +128,10 @@ dotdot:
 	if (!*dest)
 		dest = ".";
 	path = bltinlookup("CDPATH");
-	while (path) {
-		c = *path;
-		p = padvance(&path, dest);
+	while (p = path, (len = padvance(&path, dest)) >= 0) {
+		c = *p;
+		p = stalloc(len);
+
 		if (stat(p, &statb) >= 0 && S_ISDIR(statb.st_mode)) {
 			if (c && c != ':')
 				flags |= CD_PRINT;
diff --git a/usr/dash/exec.c b/usr/dash/exec.c
index c98f14c0..04ee2ba9 100644
--- a/usr/dash/exec.c
+++ b/usr/dash/exec.c
@@ -118,13 +118,13 @@ shellexec(char **argv, const char *path, int idx)
 		e = errno;
 	} else {
 		e = ENOENT;
-		while ((cmdname = padvance(&path, argv[0])) != NULL) {
+		while (padvance(&path, argv[0]) >= 0) {
+			cmdname = stackblock();
 			if (--idx < 0 && pathopt == NULL) {
 				tryexec(cmdname, argv, envp);
 				if (errno != ENOENT && errno != ENOTDIR)
 					e = errno;
 			}
-			stunalloc(cmdname);
 		}
 	}
 
@@ -182,8 +182,7 @@ repeat:
 
 const char *pathopt;
 
-char *
-padvance(const char **path, const char *name)
+int padvance(const char **path, const char *name)
 {
 	const char *p;
 	char *q;
@@ -191,7 +190,7 @@ padvance(const char **path, const char *name)
 	size_t len;
 
 	if (*path == NULL)
-		return NULL;
+		return -1;
 	start = *path;
 	for (p = start ; *p && *p != ':' && *p != '%'
; p++);
 	len = p - start + strlen(name) + 2;	/* "2" is for '/' and
'\0' */
@@ -211,7 +210,7 @@ padvance(const char **path, const char *name)
 		*path = p + 1;
 	else
 		*path = NULL;
-	return stalloc(len);
+	return len;
 }
 
 
@@ -266,9 +265,9 @@ printentry(struct tblentry *cmdp)
 	idx = cmdp->param.index;
 	path = pathval();
 	do {
-		name = padvance(&path, cmdp->cmdname);
-		stunalloc(name);
+		padvance(&path, cmdp->cmdname);
 	} while (--idx >= 0);
+	name = stackblock();
 	out1str(name);
 	out1fmt(snlfmt, cmdp->rehash ? "*" : nullstr);
 }
@@ -291,6 +290,7 @@ find_command(char *name, struct cmdentry *entry, int act,
const char *path)
 	int e;
 	int updatetbl;
 	struct builtincmd *bcmd;
+	int len;
 
 	/* If name contains a slash, don't use PATH or hash table */
 	if (strchr(name, '/') != NULL) {
@@ -362,8 +362,8 @@ find_command(char *name, struct cmdentry *entry, int act,
const char *path)
 	e = ENOENT;
 	idx = -1;
 loop:
-	while ((fullname = padvance(&path, name)) != NULL) {
-		stunalloc(fullname);
+	while ((len = padvance(&path, name)) >= 0) {
+		fullname = stackblock();
 		idx++;
 		if (pathopt) {
 			if (prefix(pathopt, "builtin")) {
@@ -398,7 +398,7 @@ loop:
 		if (!S_ISREG(statb.st_mode))
 			continue;
 		if (pathopt) {		/* this is a %func directory */
-			stalloc(strlen(fullname) + 1);
+			stalloc(len);
 			readcmdfile(fullname);
 			if ((cmdp = cmdlookup(name, 0)) == NULL ||
 			    cmdp->cmdtype != CMDFUNCTION)
@@ -789,9 +789,9 @@ describe_command(out, command, path, verbose)
 			p = command;
 		} else {
 			do {
-				p = padvance(&path, command);
-				stunalloc(p);
+				padvance(&path, command);
 			} while (--j >= 0);
+			p = stackblock();
 		}
 		if (verbose) {
 			outfmt(
diff --git a/usr/dash/exec.h b/usr/dash/exec.h
index 9ccb305f..e241b742 100644
--- a/usr/dash/exec.h
+++ b/usr/dash/exec.h
@@ -62,7 +62,7 @@ extern const char *pathopt;	/* set by padvance */
 
 void shellexec(char **, const char *, int)
     __attribute__((__noreturn__));
-char *padvance(const char **, const char *);
+int padvance(const char **, const char *);
 int hashcmd(int, char **);
 void find_command(char *, struct cmdentry *, int, const char *);
 struct builtincmd *find_builtin(const char *);
diff --git a/usr/dash/mail.c b/usr/dash/mail.c
index 02e07f77..7f9e49de 100644
--- a/usr/dash/mail.c
+++ b/usr/dash/mail.c
@@ -77,9 +77,12 @@ chkmail(void)
 	setstackmark(&smark);
 	mpath = mpathset() ? mpathval() : mailval();
 	for (mtp = mailtime; mtp < mailtime + MAXMBOXES; mtp++) {
-		p = padvance(&mpath, nullstr);
-		if (p == NULL)
+		int len;
+
+		len = padvance(&mpath, nullstr);
+		if (!len)
 			break;
+		p = stackblock();
 		if (*p == '\0')
 			continue;
 		for (q = p ; *q ; q++);
diff --git a/usr/dash/main.c b/usr/dash/main.c
index 8b351189..c87fbd73 100644
--- a/usr/dash/main.c
+++ b/usr/dash/main.c
@@ -292,20 +292,18 @@ find_dot_file(char *basename)
 	char *fullname;
 	const char *path = pathval();
 	struct stat statb;
+	int len;
 
 	/* don't try this for absolute or relative paths */
 	if (strchr(basename, '/'))
 		return basename;
 
-	while ((fullname = padvance(&path, basename)) != NULL) {
+	while ((len = padvance(&path, basename)) >= 0) {
+		fullname = stackblock();
 		if ((stat(fullname, &statb) == 0) && S_ISREG(statb.st_mode)) {
-			/*
-			 * Don't bother freeing here, since it will
-			 * be freed by the caller.
-			 */
-			return fullname;
+			/* This will be freed by the caller. */
+			return stalloc(len);
 		}
-		stunalloc(fullname);
 	}
 
 	/* not found in the PATH */