Implement fdlopen(3), an rtld interface to load shared object by file

descriptor.

Requested and tested by:	des (previous version)
Reviewed by:  des, kan (previous version)
MFC after:    2 weeks

4 files changed, 47 insertions, 3 deletions

diff --git a/lib/libc/gen/Makefile.inc b/lib/libc/gen/Makefile.inc
index 1e068a5..11d1a58 100644
--- a/lib/libc/gen/Makefile.inc
+++ b/lib/libc/gen/Makefile.inc
@@ -95,8 +95,8 @@ MLINKS+=directory.3 closedir.3 directory.3 dirfd.3 directory.3 opendir.3 \
 	directory.3 fdopendir.3 \
 	directory.3 readdir.3 directory.3 readdir_r.3 directory.3 rewinddir.3 \
 	directory.3 seekdir.3 directory.3 telldir.3
-MLINKS+=dlopen.3 dlclose.3 dlopen.3 dlerror.3 dlopen.3 dlfunc.3 \
-	dlopen.3 dlsym.3
+MLINKS+=dlopen.3 fdlopen.3 dlopen.3 dlclose.3 dlopen.3 dlerror.3 \
+	dlopen.3 dlfunc.3 dlopen.3 dlsym.3
 MLINKS+=err.3 err_set_exit.3 err.3 err_set_file.3 err.3 errc.3 err.3 errx.3 \
 	err.3 verr.3 err.3 verrc.3 err.3 verrx.3 err.3 vwarn.3 err.3 vwarnc.3 \
 	err.3 vwarnx.3 err.3 warnc.3 err.3 warn.3 err.3 warnx.3
diff --git a/lib/libc/gen/Symbol.map b/lib/libc/gen/Symbol.map
index adc5964..e00e746 100644
--- a/lib/libc/gen/Symbol.map
+++ b/lib/libc/gen/Symbol.map
@@ -382,6 +382,7 @@ FBSD_1.2 {
 };
 
 FBSD_1.3 {
+	 fdlopen;
 	__FreeBSD_libc_enter_restricted_mode;
 };
 
diff --git a/lib/libc/gen/dlfcn.c b/lib/libc/gen/dlfcn.c
index b109cc9..7be9f87 100644
--- a/lib/libc/gen/dlfcn.c
+++ b/lib/libc/gen/dlfcn.c
@@ -147,6 +147,15 @@ dl_iterate_phdr(int (*callback)(struct dl_phdr_info *, size_t, void *),
 	return 0;
 }
 
+#pragma weak fdlopen
+void *
+fdlopen(int fd, int mode)
+{
+
+	_rtld_error(sorry);
+	return NULL;
+}
+
 #pragma weak _rtld_atfork_pre
 void
 _rtld_atfork_pre(int *locks)
diff --git a/lib/libc/gen/dlopen.3 b/lib/libc/gen/dlopen.3
index 3da9b6e..089e631 100644
--- a/lib/libc/gen/dlopen.3
+++ b/lib/libc/gen/dlopen.3
@@ -32,11 +32,12 @@
 .\" @(#) dlopen.3 1.6 90/01/31 SMI
 .\" $FreeBSD$
 .\"
-.Dd July 7, 2009
+.Dd December 21, 2011
 .Dt DLOPEN 3
 .Os
 .Sh NAME
 .Nm dlopen ,
+.Nm fdlopen ,
 .Nm dlsym ,
 .Nm dlfunc ,
 .Nm dlerror ,
@@ -49,6 +50,8 @@
 .Ft void *
 .Fn dlopen "const char *path" "int mode"
 .Ft void *
+.Fn fdlopen "int fd" "int mode"
+.Ft void *
 .Fn dlsym "void * restrict handle" "const char * restrict symbol"
 .Ft dlfunc_t
 .Fn dlfunc "void * restrict handle" "const char * restrict symbol"
@@ -164,6 +167,36 @@ be interrogated with
 .Fn dlerror .
 .Pp
 The
+.Fn fdlopen
+function is similar to
+.Fn dlopen ,
+but it takes the file descriptor argument
+.Fa fd ,
+which is used for the file operations needed to load an object
+into the address space.
+The file descriptor
+.Fa fd
+is not closed by the function regardless a result of execution,
+but a duplicate of the file descriptor is.
+This may be important if a
+.Xr lockf 3
+lock is held on the passed descriptor.
+The
+.Fa fd
+argument -1 is interpreted as a reference to the main
+executable of the process, similar to
+.Va NULL
+value for the
+.Fa name
+argument to
+.Fn dlopen .
+The
+.Fn fdlopen
+function can be used by the code that needs to perform
+additional checks on the loaded objects, to prevent races with
+symlinking or renames.
+.Pp
+The
 .Fn dlsym
 function
 returns the address binding of the symbol described in the null-terminated
@@ -354,6 +387,7 @@ option to the C language compiler.
 .Sh ERRORS
 The
 .Fn dlopen ,
+.Fn fdlopen ,
 .Fn dlsym ,
 and
 .Fn dlfunc