OS-3925 lxbrand in-kernel link(2) and linkat(2)

OS-5094 lxbrand link to symlink failure
Reviewed by: Jerry Jelinek <jerry.jelinek@joyent.com>

7 files changed, 110 insertions, 84 deletions

diff --git a/usr/src/lib/brand/lx/lx_brand/common/file.c b/usr/src/lib/brand/lx/lx_brand/common/file.c
index 0654ac5c3e..79dc5e060d 100644
--- a/usr/src/lib/brand/lx/lx_brand/common/file.c
+++ b/usr/src/lib/brand/lx/lx_brand/common/file.c
@@ -22,7 +22,7 @@
 /*
  * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
  * Use is subject to license terms.
- * Copyright 2015 Joyent, Inc.  All rights reserved.
+ * Copyright 2016 Joyent, Inc.
  */
 
 #include <sys/fstyp.h>
@@ -120,23 +120,6 @@ ltos_at_flag(int lflag, int allow, boolean_t enforce)
  */
 
 /*
- * On Linux, even root cannot create a link to a directory, so we have to
- * add an explicit check.
- */
-long
-lx_link(uintptr_t p1, uintptr_t p2)
-{
-	char *from = (char *)p1;
-	char *to = (char *)p2;
-	struct stat64 statbuf;
-
-	if ((stat64(from, &statbuf) == 0) && S_ISDIR(statbuf.st_mode))
-		return (-EPERM);
-
-	return (link(from, to) ? -errno : 0);
-}
-
-/*
  * On Linux, an unlink of a directory returns EISDIR, not EPERM.
  */
 long
@@ -633,61 +616,6 @@ lx_symlinkat(uintptr_t p1, uintptr_t ext1, uintptr_t p2)
 }
 
 long
-lx_linkat(uintptr_t ext1, uintptr_t p1, uintptr_t ext2, uintptr_t p2,
-    uintptr_t p3)
-{
-	int atfd1 = (int)ext1;
-	int atfd2 = (int)ext2;
-	char pathbuf1[MAXPATHLEN];
-	char pathbuf2[MAXPATHLEN];
-	int ret;
-
-	/*
-	 * The flag specifies whether the hardlink will point to a symlink or
-	 * not, on solaris the default behaviour of link() is to dereference a
-	 * symlink and there is no obvious way to trigger the other behaviour.
-	 * So for now we just ignore this flag and act like link().
-	 */
-	int flag = p3;
-
-	/* return proper error for invalid flags */
-	if ((flag & ~(LX_AT_SYMLINK_FOLLOW | LX_AT_EMPTY_PATH)) != 0)
-		return (-EINVAL);
-
-	ret = getpathat(atfd1, p1, pathbuf1, sizeof (pathbuf1));
-	if (ret < 0) {
-		if (ret == -EBADF) {
-			/*
-			 * Try to figure out correct Linux errno. We know path
-			 * is relative. Check if we have a fd for a dir which
-			 * has been removed.
-			 */
-			if (atfd1 != -1 && lx_fd_to_path(atfd1, pathbuf1,
-			    sizeof (pathbuf1)) == NULL)
-				ret = -ENOENT;
-		}
-		return (ret);
-	}
-
-	ret = getpathat(atfd2, p2, pathbuf2, sizeof (pathbuf2));
-	if (ret < 0) {
-		if (ret == -EBADF) {
-			/*
-			 * Try to figure out correct Linux errno. We know path
-			 * is relative. Check if we have a fd for a dir which
-			 * has been removed.
-			 */
-			if (atfd2 != -1 && lx_fd_to_path(atfd2, pathbuf2,
-			    sizeof (pathbuf2)) == NULL)
-				ret = -ENOENT;
-		}
-		return (ret);
-	}
-
-	return (lx_link((uintptr_t)pathbuf1, (uintptr_t)pathbuf2));
-}
-
-long
 lx_readlink(uintptr_t p1, uintptr_t p2, uintptr_t p3)
 {
 	int ret;
diff --git a/usr/src/lib/brand/lx/lx_brand/common/lx_brand.c b/usr/src/lib/brand/lx/lx_brand/common/lx_brand.c
index bc3c1921f3..582c2f0b55 100644
--- a/usr/src/lib/brand/lx/lx_brand/common/lx_brand.c
+++ b/usr/src/lib/brand/lx/lx_brand/common/lx_brand.c
@@ -1045,7 +1045,7 @@ static lx_syscall_handler_t lx_handlers[] = {
 	NULL,				/*  83: mkdir */
 	lx_rmdir,			/*  84: rmdir */
 	lx_creat,			/*  85: creat */
-	lx_link,			/*  86: link */
+	NULL,				/*  86: link */
 	lx_unlink,			/*  87: unlink */
 	lx_symlink,			/*  88: symlink */
 	lx_readlink,			/*  89: readlink */
@@ -1224,7 +1224,7 @@ static lx_syscall_handler_t lx_handlers[] = {
 	NULL,				/* 262: fstatat64 */
 	lx_unlinkat,			/* 263: unlinkat */
 	lx_renameat,			/* 264: renameat */
-	lx_linkat,			/* 265: linkat */
+	NULL,				/* 265: linkat */
 	lx_symlinkat,			/* 266: symlinkat */
 	lx_readlinkat,			/* 267: readlinkat */
 	NULL,				/* 268: fchmodat */
@@ -1299,7 +1299,7 @@ static lx_syscall_handler_t lx_handlers[] = {
 	lx_close,			/*   6: close */
 	NULL,				/*   7: waitpid */
 	lx_creat,			/*   8: creat */
-	lx_link,			/*   9: link */
+	NULL,				/*   9: link */
 	lx_unlink,			/*  10: unlink */
 	lx_execve,			/*  11: execve */
 	lx_chdir,			/*  12: chdir */
@@ -1593,7 +1593,7 @@ static lx_syscall_handler_t lx_handlers[] = {
 	NULL,				/* 300: fstatat64 */
 	lx_unlinkat,			/* 301: unlinkat */
 	lx_renameat,			/* 302: renameat */
-	lx_linkat,			/* 303: linkat */
+	NULL,				/* 303: linkat */
 	lx_symlinkat,			/* 304: symlinkat */
 	lx_readlinkat,			/* 305: readlinkat */
 	NULL,				/* 306: fchmodat */
diff --git a/usr/src/lib/brand/lx/lx_brand/sys/lx_syscall.h b/usr/src/lib/brand/lx/lx_brand/sys/lx_syscall.h
index a3f199dece..df68d4059f 100644
--- a/usr/src/lib/brand/lx/lx_brand/sys/lx_syscall.h
+++ b/usr/src/lib/brand/lx/lx_brand/sys/lx_syscall.h
@@ -25,7 +25,7 @@
  */
 
 /*
- * Copyright 2015 Joyent, Inc. All rights reserved.
+ * Copyright 2016 Joyent, Inc.
  */
 
 #ifndef _SYS_LX_SYSCALL_H
@@ -50,7 +50,6 @@ extern long lx_utimensat(uintptr_t, uintptr_t, uintptr_t, uintptr_t);
 extern long lx_fstatat64(uintptr_t, uintptr_t, uintptr_t, uintptr_t);
 extern long lx_unlinkat(uintptr_t, uintptr_t, uintptr_t);
 extern long lx_renameat(uintptr_t, uintptr_t, uintptr_t, uintptr_t);
-extern long lx_linkat(uintptr_t, uintptr_t, uintptr_t, uintptr_t, uintptr_t);
 extern long lx_symlinkat(uintptr_t, uintptr_t, uintptr_t);
 extern long lx_readlinkat(uintptr_t, uintptr_t, uintptr_t, uintptr_t);
 extern long lx_access(uintptr_t, uintptr_t);
@@ -144,7 +143,6 @@ extern long lx_ftruncate64(uintptr_t, uintptr_t, uintptr_t);
 extern long lx_sysctl(uintptr_t);
 extern long lx_fsync(uintptr_t);
 extern long lx_fdatasync(uintptr_t);
-extern long lx_link(uintptr_t, uintptr_t);
 extern long lx_unlink(uintptr_t);
 extern long lx_rmdir(uintptr_t);
 extern long lx_rename(uintptr_t, uintptr_t);
diff --git a/usr/src/uts/common/brand/lx/os/lx_syscall.c b/usr/src/uts/common/brand/lx/os/lx_syscall.c
index de4caa9a66..c6076dbe6c 100644
--- a/usr/src/uts/common/brand/lx/os/lx_syscall.c
+++ b/usr/src/uts/common/brand/lx/os/lx_syscall.c
@@ -625,7 +625,7 @@ lx_sysent_t lx_sysent32[] = {
 	{"close",	lx_close,		0,		1}, /*  6 */
 	{"waitpid",	lx_waitpid,		0,		3}, /*  7 */
 	{"creat",	NULL,			0,		2}, /*  8 */
-	{"link",	NULL,			0,		2}, /*  9 */
+	{"link",	lx_link,		0,		2}, /*  9 */
 	{"unlink",	NULL,			0,		1}, /* 10 */
 	{"execve",	NULL,			0,		3}, /* 11 */
 	{"chdir",	NULL,			0,		1}, /* 12 */
@@ -923,7 +923,7 @@ lx_sysent_t lx_sysent32[] = {
 	{"fstatat64",	lx_fstatat64,		0,		4}, /* 300 */
 	{"unlinkat",	NULL,			0,		3}, /* 301 */
 	{"renameat",	NULL,			0,		4}, /* 302 */
-	{"linkat",	NULL,			0,		5}, /* 303 */
+	{"linkat",	lx_linkat,		0,		5}, /* 303 */
 	{"symlinkat",	NULL,			0,		3}, /* 304 */
 	{"readlinkat",	NULL,			0,		4}, /* 305 */
 	{"fchmodat",	lx_fchmodat,		0,		3}, /* 306 */
@@ -1073,7 +1073,7 @@ lx_sysent_t lx_sysent64[] = {
 	{"mkdir",	lx_mkdir,		0,		2}, /* 83 */
 	{"rmdir",	NULL,			0,		1}, /* 84 */
 	{"creat",	NULL,			0,		2}, /* 85 */
-	{"link",	NULL,			0,		2}, /* 86 */
+	{"link",	lx_link,		0,		2}, /* 86 */
 	{"unlink",	NULL,			0,		1}, /* 87 */
 	{"symlink",	NULL,			0,		2}, /* 88 */
 	{"readlink",	NULL,			0,		3}, /* 89 */
@@ -1252,7 +1252,7 @@ lx_sysent_t lx_sysent64[] = {
 	{"fstatat64",	lx_fstatat64,		0,		4}, /* 262 */
 	{"unlinkat",	NULL,			0,		3}, /* 263 */
 	{"renameat",	NULL,			0,		4}, /* 264 */
-	{"linkat",	NULL,			0,		5}, /* 265 */
+	{"linkat",	lx_linkat,		0,		5}, /* 265 */
 	{"symlinkat",	NULL,			0,		3}, /* 266 */
 	{"readlinkat",	NULL,			0,		4}, /* 267 */
 	{"fchmodat",	lx_fchmodat,		0,		3}, /* 268 */
diff --git a/usr/src/uts/common/brand/lx/sys/lx_syscalls.h b/usr/src/uts/common/brand/lx/sys/lx_syscalls.h
index 3636c8d718..03012d70d1 100644
--- a/usr/src/uts/common/brand/lx/sys/lx_syscalls.h
+++ b/usr/src/uts/common/brand/lx/sys/lx_syscalls.h
@@ -83,6 +83,8 @@ extern long lx_ioprio_set();
 extern long lx_kill();
 extern long lx_lchown();
 extern long lx_lchown16();
+extern long lx_link();
+extern long lx_linkat();
 extern long lx_lstat32();
 extern long lx_lstat64();
 extern long lx_mkdir();
diff --git a/usr/src/uts/common/brand/lx/syscall/lx_link.c b/usr/src/uts/common/brand/lx/syscall/lx_link.c
new file mode 100644
index 0000000000..23e0768581
--- /dev/null
+++ b/usr/src/uts/common/brand/lx/syscall/lx_link.c
@@ -0,0 +1,97 @@
+/*
+ * This file and its contents are supplied under the terms of the
+ * Common Development and Distribution License ("CDDL"), version 1.0.
+ * You may only use this file in accordance with the terms of version
+ * 1.0 of the CDDL.
+ *
+ * A full copy of the text of the CDDL should have accompanied this
+ * source.  A copy of the CDDL is also available via the Internet at
+ * http://www.illumos.org/license/CDDL.
+ */
+
+/*
+ * Copyright 2016 Joyent, Inc.
+ */
+
+#include <sys/fcntl.h>
+#include <sys/errno.h>
+#include <sys/file.h>
+#include <sys/vnode.h>
+#include <sys/systm.h>
+#include <sys/lx_fcntl.h>
+
+#define	LX_LINK_ALLOWED	(LX_AT_SYMLINK_FOLLOW | LX_AT_EMPTY_PATH)
+
+static long
+lx_link_common(int ffd, char *from, int tfd, char *to, int flags)
+{
+	int error;
+	vnode_t *fsvp = NULL, *tsvp = NULL;
+	enum symfollow follow = NO_FOLLOW;
+
+	if ((flags & ~LX_LINK_ALLOWED) != 0) {
+		return (set_errno(EINVAL));
+	}
+	if ((flags & LX_AT_EMPTY_PATH) == 0) {
+		char c;
+
+		/*
+		 * Check that both 'from' and 'to' names are non-empty if
+		 * AT_EMPTY_PATH is not set.
+		 */
+		if (copyin(from, &c, sizeof (c)) != 0) {
+			return (set_errno(EFAULT));
+		} else if (c == '\0') {
+			return (set_errno(ENOENT));
+		}
+		if (copyin(to, &c, sizeof (c)) != 0) {
+			return (set_errno(EFAULT));
+		} else if (c == '\0') {
+			return (set_errno(ENOENT));
+		}
+
+		/*
+		 * XXX: When our support for LX capabilities improves, ENOENT
+		 * should be thrown when a process lacking CAP_DAC_READ_SEARCH
+		 * attempts to use the AT_EMPTY_PATH flag.
+		 */
+	}
+	if ((flags & LX_AT_SYMLINK_FOLLOW) != 0) {
+		follow = FOLLOW;
+	}
+
+	if ((error = fgetstartvp(ffd, from, &fsvp)) != 0) {
+		goto out;
+	}
+	if ((error = fgetstartvp(tfd, to, &tsvp)) != 0) {
+		goto out;
+	}
+	error = vn_linkat(fsvp, from, follow, tsvp, to, UIO_USERSPACE);
+
+out:
+	if (fsvp != NULL) {
+		VN_RELE(fsvp);
+	}
+	if (tsvp != NULL) {
+		VN_RELE(tsvp);
+	}
+	if (error) {
+		return (set_errno(error));
+	}
+	return (0);
+}
+
+long
+lx_link(char *from, char *to)
+{
+	return (lx_link_common(AT_FDCWD, from, AT_FDCWD, to, 0));
+}
+
+long
+lx_linkat(int ffd, char *from, int tfd, char *to, int flags)
+{
+	ffd = (ffd == LX_AT_FDCWD) ? AT_FDCWD : ffd;
+	tfd = (tfd == LX_AT_FDCWD) ? AT_FDCWD : tfd;
+
+	return (lx_link_common(ffd, from, tfd, to, flags));
+}
diff --git a/usr/src/uts/intel/Makefile.files b/usr/src/uts/intel/Makefile.files
index 463b405341..b730774ac7 100644
--- a/usr/src/uts/intel/Makefile.files
+++ b/usr/src/uts/intel/Makefile.files
@@ -312,6 +312,7 @@ LX_BRAND_OBJS  =		\
 	lx_ioctl.o		\
 	lx_ioprio.o		\
 	lx_kill.o		\
+	lx_link.o		\
 	lx_misc.o		\
 	lx_mkdir.o		\
 	lx_modify_ldt.o		\