copy realpath() from FreeBSD repo

To sandbox apps robustly, we're going to need to always work with
canonical absolute paths.

2 files changed, 245 insertions, 1 deletions

diff --git a/src/Makefile b/src/Makefile
index c1334ad..a9f39a2 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -26,7 +26,7 @@ LUA_A=	liblua.a
 CORE_O=	lapi.o lcode.o ldebug.o ldo.o ldump.o lfunc.o lgc.o llex.o lmem.o \
 	lobject.o lopcodes.o lparser.o lstate.o lstring.o ltable.o ltm.o  \
 	lundump.o lvm.o lzio.o \
-	lfs.o kilo.o tlv.o teliva.o
+	realpath.o lfs.o kilo.o tlv.o teliva.o
 LIB_O=	lauxlib.o lbaselib.o ldblib.o liolib.o lmathlib.o loslib.o \
 	ltablib.o lstrlib.o loadlib.o linit.o
 
@@ -189,6 +189,7 @@ lzio.o: lzio.c lua.h luaconf.h llimits.h lmem.h lstate.h lobject.h ltm.h \
   lzio.h
 print.o: print.c ldebug.h lstate.h lua.h luaconf.h lobject.h llimits.h \
   ltm.h lzio.h lmem.h lopcodes.h lundump.h
+realpath.o: realpath.c
 lfs.o: lfs.c lfs.h lua.h lauxlib.h lualib.h
 kilo.o: kilo.c lua.h teliva.h
 teliva.o: teliva.c lua.h lauxlib.h lualib.h teliva.h tlv.h
diff --git a/src/realpath.c b/src/realpath.c
new file mode 100644
index 0000000..dc57bbb
--- /dev/null
+++ b/src/realpath.c
@@ -0,0 +1,243 @@
+/*
+ * Copyright (c) 2003 Constantin S. Svintsoff <kostik@iclub.nsu.ru>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. The names of the authors may not be used to endorse or promote
+ *    products derived from this software without specific prior written
+ *    permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+
+#include <sys/param.h>
+#include <sys/stat.h>
+
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+/*
+ * Find the real name of path, by removing all ".", ".." and symlink
+ * components.  Returns (resolved) on success, or (NULL) on failure,
+ * in which case the path which caused trouble is left in (resolved).
+ */
+char *
+realpath(const char * __restrict path, char * __restrict resolved)
+{
+	struct stat sb;
+	char *p, *q, *s;
+	size_t left_len, resolved_len;
+	unsigned symlinks;
+	int m, slen;
+	char left[PATH_MAX], next_token[PATH_MAX], symlink[PATH_MAX];
+
+	if (path == NULL) {
+		errno = EINVAL;
+		return (NULL);
+	}
+	if (path[0] == '\0') {
+		errno = ENOENT;
+		return (NULL);
+	}
+	if (resolved == NULL) {
+		resolved = malloc(PATH_MAX);
+		if (resolved == NULL)
+			return (NULL);
+		m = 1;
+	} else
+		m = 0;
+	symlinks = 0;
+	if (path[0] == '/') {
+		resolved[0] = '/';
+		resolved[1] = '\0';
+		if (path[1] == '\0')
+			return (resolved);
+		resolved_len = 1;
+		left_len = strlcpy(left, path + 1, sizeof(left));
+	} else {
+		if (getcwd(resolved, PATH_MAX) == NULL) {
+			if (m)
+				free(resolved);
+			else {
+				resolved[0] = '.';
+				resolved[1] = '\0';
+			}
+			return (NULL);
+		}
+		resolved_len = strlen(resolved);
+		left_len = strlcpy(left, path, sizeof(left));
+	}
+	if (left_len >= sizeof(left) || resolved_len >= PATH_MAX) {
+		if (m)
+			free(resolved);
+		errno = ENAMETOOLONG;
+		return (NULL);
+	}
+
+	/*
+	 * Iterate over path components in `left'.
+	 */
+	while (left_len != 0) {
+		/*
+		 * Extract the next path component and adjust `left'
+		 * and its length.
+		 */
+		p = strchr(left, '/');
+		s = p ? p : left + left_len;
+		if (s - left >= sizeof(next_token)) {
+			if (m)
+				free(resolved);
+			errno = ENAMETOOLONG;
+			return (NULL);
+		}
+		memcpy(next_token, left, s - left);
+		next_token[s - left] = '\0';
+		left_len -= s - left;
+		if (p != NULL)
+			memmove(left, s + 1, left_len + 1);
+		if (resolved[resolved_len - 1] != '/') {
+			if (resolved_len + 1 >= PATH_MAX) {
+				if (m)
+					free(resolved);
+				errno = ENAMETOOLONG;
+				return (NULL);
+			}
+			resolved[resolved_len++] = '/';
+			resolved[resolved_len] = '\0';
+		}
+		if (next_token[0] == '\0') {
+			/*
+			 * Handle consequential slashes.  The path
+			 * before slash shall point to a directory.
+			 *
+			 * Only the trailing slashes are not covered
+			 * by other checks in the loop, but we verify
+			 * the prefix for any (rare) "//" or "/\0"
+			 * occurrence to not implement lookahead.
+			 */
+			if (lstat(resolved, &sb) != 0) {
+				if (m)
+					free(resolved);
+				return (NULL);
+			}
+			if (!S_ISDIR(sb.st_mode)) {
+				if (m)
+					free(resolved);
+				errno = ENOTDIR;
+				return (NULL);
+			}
+			continue;
+		}
+		else if (strcmp(next_token, ".") == 0)
+			continue;
+		else if (strcmp(next_token, "..") == 0) {
+			/*
+			 * Strip the last path component except when we have
+			 * single "/"
+			 */
+			if (resolved_len > 1) {
+				resolved[resolved_len - 1] = '\0';
+				q = strrchr(resolved, '/') + 1;
+				*q = '\0';
+				resolved_len = q - resolved;
+			}
+			continue;
+		}
+
+		/*
+		 * Append the next path component and lstat() it.
+		 */
+		resolved_len = strlcat(resolved, next_token, PATH_MAX);
+		if (resolved_len >= PATH_MAX) {
+			if (m)
+				free(resolved);
+			errno = ENAMETOOLONG;
+			return (NULL);
+		}
+		if (lstat(resolved, &sb) != 0) {
+			if (m)
+				free(resolved);
+			return (NULL);
+		}
+		if (S_ISLNK(sb.st_mode)) {
+			if (symlinks++ > MAXSYMLINKS) {
+				if (m)
+					free(resolved);
+				errno = ELOOP;
+				return (NULL);
+			}
+			slen = readlink(resolved, symlink, sizeof(symlink) - 1);
+			if (slen < 0) {
+				if (m)
+					free(resolved);
+				return (NULL);
+			}
+			symlink[slen] = '\0';
+			if (symlink[0] == '/') {
+				resolved[1] = 0;
+				resolved_len = 1;
+			} else if (resolved_len > 1) {
+				/* Strip the last path component. */
+				resolved[resolved_len - 1] = '\0';
+				q = strrchr(resolved, '/') + 1;
+				*q = '\0';
+				resolved_len = q - resolved;
+			}
+
+			/*
+			 * If there are any path components left, then
+			 * append them to symlink. The result is placed
+			 * in `left'.
+			 */
+			if (p != NULL) {
+				if (symlink[slen - 1] != '/') {
+					if (slen + 1 >= sizeof(symlink)) {
+						if (m)
+							free(resolved);
+						errno = ENAMETOOLONG;
+						return (NULL);
+					}
+					symlink[slen] = '/';
+					symlink[slen + 1] = 0;
+				}
+				left_len = strlcat(symlink, left,
+				    sizeof(symlink));
+				if (left_len >= sizeof(left)) {
+					if (m)
+						free(resolved);
+					errno = ENAMETOOLONG;
+					return (NULL);
+				}
+			}
+			left_len = strlcpy(left, symlink, sizeof(left));
+		}
+	}
+
+	/*
+	 * Remove trailing slash except when the resolved pathname
+	 * is a single "/".
+	 */
+	if (resolved_len > 1 && resolved[resolved_len - 1] == '/')
+		resolved[resolved_len - 1] = '\0';
+	return (resolved);
+}