From 1963fa800f4554d729f14f7f3a01a5b4af4dfbc1 Mon Sep 17 00:00:00 2001
From: "A. Wilcox" <AWilcox@Wilcox-Tech.com>
Date: Thu, 14 Mar 2019 11:14:38 -0500
Subject: renameat: further bring towards standard behaviour

---
 src/unistd/renameat.c | 35 ++++++++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

diff --git a/src/unistd/renameat.c b/src/unistd/renameat.c
index 07386407..d0f31c21 100644
--- a/src/unistd/renameat.c
+++ b/src/unistd/renameat.c
@@ -1,16 +1,23 @@
 #include <errno.h>
+#include <fcntl.h>
 #include <libgen.h>
 #include <limits.h>
 #include <stdio.h>
 #include <string.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
 #include "syscall.h"
 
 int renameat(int oldfd, const char *old, int newfd, const char *new)
 {
 	char old_copy[PATH_MAX+1], new_copy[PATH_MAX+1];
 	char *base;
+	size_t old_size, new_size;
+	struct stat statbuf;
 
-	if (strlen(old) > PATH_MAX || strlen(new) > PATH_MAX) {
+	if ((old_size = strlen(old)) > PATH_MAX || \
+	    (new_size = strlen(new)) > PATH_MAX) {
 		errno = ENAMETOOLONG;
 		return -1;
 	}
@@ -34,5 +41,31 @@ int renameat(int oldfd, const char *old, int newfd, const char *new)
 		return -1;
 	}
 
+	/* The Linux kernel will fail when attempting to rename a symlink of a
+	   directory with a trailing slash.  We therefore have to handle this
+	   case ourselves. */
+	if (old[old_size - 1] == '/') {
+		/* Calling stat(2) on a symlink to a dir with the trailing
+		   slash causes stat(2) to return the actual directory instead
+		   of the symlink itself. */
+		strcpy(old_copy, old);
+		old_copy[old_size - 1] = '\0';
+		if (fstatat(oldfd, old_copy, &statbuf, AT_SYMLINK_NOFOLLOW) == -1) {
+			return -1;
+		}
+		if (S_ISLNK(statbuf.st_mode)) {
+			if (fstatat(oldfd, old, &statbuf, 0) == -1) {
+				return -1;
+			}
+			if (S_ISDIR(statbuf.st_mode)) {
+				old = old_copy;
+			} else {
+				/* may as well not waste the syscall */
+				errno = ENOTDIR;
+				return -1;
+			}
+		}
+	}
+
 	return syscall(SYS_renameat, oldfd, old, newfd, new);
 }
-- 
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