According to SUSv4, realpath(3) must fail if

[ENOENT]  A component of file_name does not name an existing file or
    file_name points to an empty string.
[ENOTDIR] A component of the path prefix is not a directory, or the
    file_name argument contains at least one non- <slash> character
    and ends with one or more trailing <slash> characters and the last
    pathname component names an existing file that is neither a
    directory nor a symbolic link to a directory.
Add checks for the listed conditions, and set errno accordingly.

Update the realpath(3) manpage to mention SUS behaviour. Remove the
requirement to include sys/param.h before stdlib.h.

PR:	    128933
MFC after:  3 weeks

2 files changed, 29 insertions, 12 deletions

diff --git a/lib/libc/stdlib/realpath.3 b/lib/libc/stdlib/realpath.3
index fec5258..c7384d6 100644
--- a/lib/libc/stdlib/realpath.3
+++ b/lib/libc/stdlib/realpath.3
@@ -31,7 +31,7 @@
 .\"     @(#)realpath.3	8.2 (Berkeley) 2/16/94
 .\" $FreeBSD$
 .\"
-.Dd April 19, 2010
+.Dd May 11, 2012
 .Dt REALPATH 3
 .Os
 .Sh NAME
@@ -40,7 +40,6 @@
 .Sh LIBRARY
 .Lb libc
 .Sh SYNOPSIS
-.In sys/param.h
 .In stdlib.h
 .Ft "char *"
 .Fn realpath "const char *pathname" "char *resolved_path"
@@ -72,11 +71,12 @@ The
 function will resolve both absolute and relative paths
 and return the absolute pathname corresponding to
 .Fa pathname .
-All but the last component of
+All components of
 .Fa pathname
 must exist when
 .Fn realpath
-is called.
+is called, and all but the last component must name either directories or
+symlinks pointing to the directories.
 .Sh "RETURN VALUES"
 The
 .Fn realpath
diff --git a/lib/libc/stdlib/realpath.c b/lib/libc/stdlib/realpath.c
index 2c9562e..ffbf8ec 100644
--- a/lib/libc/stdlib/realpath.c
+++ b/lib/libc/stdlib/realpath.c
@@ -132,8 +132,29 @@ realpath(const char * __restrict path, char * __restrict resolved)
 			resolved[resolved_len++] = '/';
 			resolved[resolved_len] = '\0';
 		}
-		if (next_token[0] == '\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"
+			 * occurence 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) {
@@ -151,9 +172,7 @@ realpath(const char * __restrict path, char * __restrict resolved)
 		}
 
 		/*
-		 * Append the next path component and lstat() it. If
-		 * lstat() fails we still can return successfully if
-		 * there are no more path components left.
+		 * Append the next path component and lstat() it.
 		 */
 		resolved_len = strlcat(resolved, next_token, PATH_MAX);
 		if (resolved_len >= PATH_MAX) {
@@ -163,10 +182,8 @@ realpath(const char * __restrict path, char * __restrict resolved)
 			return (NULL);
 		}
 		if (lstat(resolved, &sb) != 0) {
-			if (errno == ENOENT && p == NULL) {
-				errno = serrno;
-				return (resolved);
-			}
+			if (errno != ENOENT || p != NULL)
+				errno = ENOTDIR;
 			if (m)
 				free(resolved);
 			return (NULL);