From 671ea40f626ff98064442834e386a49b009b144d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=D0=BD=D0=B0=D0=B1?= <nabijaczleweli@nabijaczleweli.xyz>
Date: Wed, 26 May 2021 19:03:47 +0200
Subject: [PATCH] freebsd/libzfs: import execvPe() from FreeBSD 13
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It allocates less and properly deals with argv={NULL}

With minor cosmetic changes to match cstyle, remove whitespace damage,
and restore direct string printing

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ryan Moeller <ryan@ixsystems.com>
Reviewed-by: Tony Nguyen <tony.nguyen@delphix.com>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #12051
---
 lib/libzfs/os/freebsd/libzfs_compat.c | 61 ++++++++++++++++++---------
 1 file changed, 42 insertions(+), 19 deletions(-)

diff --git a/lib/libzfs/os/freebsd/libzfs_compat.c b/lib/libzfs/os/freebsd/libzfs_compat.c
index 0e8a3b1217..3c5f684c68 100644
--- a/lib/libzfs/os/freebsd/libzfs_compat.c
+++ b/lib/libzfs/os/freebsd/libzfs_compat.c
@@ -52,8 +52,8 @@ execvPe(const char *name, const char *path, char * const *argv,
 	const char **memp;
 	size_t cnt, lp, ln;
 	int eacces, save_errno;
-	char *cur, buf[MAXPATHLEN];
-	const char *p, *bp;
+	char buf[MAXPATHLEN];
+	const char *bp, *np, *op, *p;
 	struct stat sb;
 
 	eacces = 0;
@@ -61,7 +61,7 @@ execvPe(const char *name, const char *path, char * const *argv,
 	/* If it's an absolute or relative path name, it's easy. */
 	if (strchr(name, '/')) {
 		bp = name;
-		cur = NULL;
+		op = NULL;
 		goto retry;
 	}
 	bp = buf;
@@ -72,23 +72,30 @@ execvPe(const char *name, const char *path, char * const *argv,
 		return (-1);
 	}
 
-	cur = alloca(strlen(path) + 1);
-	if (cur == NULL) {
-		errno = ENOMEM;
-		return (-1);
-	}
-	strcpy(cur, path);
-	while ((p = strsep(&cur, ":")) != NULL) {
+	op = path;
+	ln = strlen(name);
+	while (op != NULL) {
+		np = strchrnul(op, ':');
+
 		/*
 		 * It's a SHELL path -- double, leading and trailing colons
 		 * mean the current directory.
 		 */
-		if (*p == '\0') {
+		if (np == op) {
+			/* Empty component. */
 			p = ".";
 			lp = 1;
-		} else
-			lp = strlen(p);
-		ln = strlen(name);
+		} else {
+			/* Non-empty component. */
+			p = op;
+			lp = np - op;
+		}
+
+		/* Advance to the next component or terminate after this. */
+		if (*np == '\0')
+			op = NULL;
+		else
+			op = np + 1;
 
 		/*
 		 * If the path is too long complain.  This is a possible
@@ -118,15 +125,31 @@ retry:		(void) execve(bp, argv, envp);
 		case ENOEXEC:
 			for (cnt = 0; argv[cnt]; ++cnt)
 				;
-			memp = alloca((cnt + 2) * sizeof (char *));
+
+			/*
+			 * cnt may be 0 above; always allocate at least
+			 * 3 entries so that we can at least fit "sh", bp, and
+			 * the NULL terminator.  We can rely on cnt to take into
+			 * account the NULL terminator in all other scenarios,
+			 * as we drop argv[0].
+			 */
+			memp = alloca(MAX(3, cnt + 2) * sizeof (char *));
 			if (memp == NULL) {
 				/* errno = ENOMEM; XXX override ENOEXEC? */
 				goto done;
 			}
-			memp[0] = "sh";
-			memp[1] = bp;
-			bcopy(argv + 1, memp + 2, cnt * sizeof (char *));
-			execve(_PATH_BSHELL, __DECONST(char **, memp), envp);
+			if (cnt > 0) {
+				memp[0] = argv[0];
+				memp[1] = bp;
+				bcopy(argv + 1, memp + 2,
+				    cnt * sizeof (char *));
+			} else {
+				memp[0] = "sh";
+				memp[1] = bp;
+				memp[2] = NULL;
+			}
+			(void) execve(_PATH_BSHELL,
+			    __DECONST(char **, memp), envp);
 			goto done;
 		case ENOMEM:
 			goto done;