Add O_PATH support for flistxattr()

A continuation of commit 2825f10b7f61558c264231a536cf3affc0d84204.

Add O_PATH compatibility support for flistxattr(). This allows
a process to list out all the extended attributes associated with
O_PATH file descriptors.

Change-Id: Ie2285ac7ad2e4eac427ddba6c2d182d41b130f75

libc/Android.mk

@@ -130,6 +130,7 @@ libc_bionic_ndk_src_files := \
     bionic/fchmodat.cpp \
     bionic/ffs.cpp \
     bionic/fgetxattr.cpp \
+    bionic/flistxattr.cpp \
     bionic/flockfile.cpp \
     bionic/fpclassify.cpp \
     bionic/fsetxattr.cpp \

libc/SYSCALLS.TXT

@@ -124,7 +124,7 @@ int         fchown:fchown(int, uid_t, gid_t)    arm64,mips,mips64,x86_64
 void        sync(void)  all
 int         ___fsetxattr:fsetxattr(int, const char*, const void*, size_t, int) all
 ssize_t     ___fgetxattr:fgetxattr(int, const char*, void*, size_t) all
-ssize_t     flistxattr(int, char*, size_t) all
+ssize_t     ___flistxattr:flistxattr(int, char*, size_t) all
 int         fremovexattr(int, const char*) all
 
 int __getdents64:getdents64(unsigned int, struct dirent*, unsigned int)   arm,arm64,mips,mips64,x86,x86_64

libc/arch-arm/syscalls/___flistxattr.S

@@ -2,7 +2,7 @@
 
 #include <private/bionic_asm.h>
 
-ENTRY(flistxattr)
+ENTRY(___flistxattr)
     mov     ip, r7
     ldr     r7, =__NR_flistxattr
     swi     #0
@@ -11,4 +11,5 @@ ENTRY(flistxattr)
     bxls    lr
     neg     r0, r0
     b       __set_errno_internal
-END(flistxattr)
+END(___flistxattr)
+.hidden ___flistxattr

libc/arch-arm64/syscalls/___flistxattr.S

@@ -2,7 +2,7 @@
 
 #include <private/bionic_asm.h>
 
-ENTRY(flistxattr)
+ENTRY(___flistxattr)
     mov     x8, __NR_flistxattr
     svc     #0
 
@@ -11,4 +11,5 @@ ENTRY(flistxattr)
     b.hi    __set_errno_internal
 
     ret
-END(flistxattr)
+END(___flistxattr)
+.hidden ___flistxattr

libc/arch-mips/syscalls/___flistxattr.S

@@ -2,7 +2,7 @@
 
 #include <private/bionic_asm.h>
 
-ENTRY(flistxattr)
+ENTRY(___flistxattr)
     .set noreorder
     .cpload t9
     li v0, __NR_flistxattr
@@ -16,4 +16,5 @@ ENTRY(flistxattr)
     j t9
     nop
     .set reorder
-END(flistxattr)
+END(___flistxattr)
+.hidden ___flistxattr

libc/arch-mips64/syscalls/___flistxattr.S

@@ -2,7 +2,7 @@
 
 #include <private/bionic_asm.h>
 
-ENTRY(flistxattr)
+ENTRY(___flistxattr)
     .set push
     .set noreorder
     li v0, __NR_flistxattr
@@ -22,4 +22,5 @@ ENTRY(flistxattr)
     j t9
     move ra, t0
     .set pop
-END(flistxattr)
+END(___flistxattr)
+.hidden ___flistxattr

libc/arch-x86/syscalls/___flistxattr.S

@@ -2,7 +2,7 @@
 
 #include <private/bionic_asm.h>
 
-ENTRY(flistxattr)
+ENTRY(___flistxattr)
     pushl   %ebx
     .cfi_def_cfa_offset 8
     .cfi_rel_offset ebx, 0
@@ -28,4 +28,5 @@ ENTRY(flistxattr)
     popl    %ecx
     popl    %ebx
     ret
-END(flistxattr)
+END(___flistxattr)
+.hidden ___flistxattr

libc/arch-x86_64/syscalls/___flistxattr.S

@@ -2,7 +2,7 @@
 
 #include <private/bionic_asm.h>
 
-ENTRY(flistxattr)
+ENTRY(___flistxattr)
     movl    $__NR_flistxattr, %eax
     syscall
     cmpq    $-MAX_ERRNO, %rax
@@ -12,4 +12,5 @@ ENTRY(flistxattr)
     call    __set_errno_internal
 1:
     ret
-END(flistxattr)
+END(___flistxattr)
+.hidden ___flistxattr

libc/bionic/flistxattr.cpp

@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * 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.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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
+ * COPYRIGHT OWNER 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/stat.h>
+#include <sys/types.h>
+#include <sys/xattr.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+
+extern "C" ssize_t ___flistxattr(int, char*, size_t);
+
+ssize_t flistxattr(int fd, char *list, size_t size) {
+  int saved_errno = errno;
+  ssize_t result = ___flistxattr(fd, list, size);
+
+  if ((result != -1) || (errno != EBADF)) {
+    return result;
+  }
+
+  // fd could be an O_PATH file descriptor, and the kernel
+  // may not directly support fgetxattr() on such a file descriptor.
+  // Use /proc/self/fd instead to emulate this support.
+  int fd_flag = fcntl(fd, F_GETFL);
+  if ((fd_flag == -1) || ((fd_flag & O_PATH) == 0)) {
+    errno = EBADF;
+    return -1;
+  }
+
+  char buf[40];
+  snprintf(buf, sizeof(buf), "/proc/self/fd/%d", fd);
+  errno = saved_errno;
+  return listxattr(buf, list, size);
+}

tests/sys_xattr_test.cpp

@@ -80,6 +80,7 @@ TEST(sys_xattr, fsetxattr_with_opath) {
   ASSERT_EQ(-1, res);
   ASSERT_EQ(EBADF, errno);
 #endif
+  close(fd);
 }
 
 TEST(sys_xattr, fsetxattr_with_opath_toosmall) {
@@ -97,4 +98,32 @@ TEST(sys_xattr, fsetxattr_with_opath_toosmall) {
   ASSERT_EQ(-1, res);
   ASSERT_EQ(EBADF, errno);
 #endif
+  close(fd);
+}
+
+TEST(sys_xattr, flistattr) {
+  TemporaryFile tf;
+  char buf[65536];  // 64kB is max possible xattr list size. See "man 7 xattr".
+  ASSERT_EQ(0, fsetxattr(tf.fd, "user.foo", "bar", 4, 0));
+  ssize_t result = flistxattr(tf.fd, buf, sizeof(buf));
+  ASSERT_TRUE(result >= 9);
+  ASSERT_TRUE(memmem(buf, sizeof(buf), "user.foo", 9) != NULL);
+}
+
+TEST(sys_xattr, flistattr_opath) {
+  TemporaryFile tf;
+  char buf[65536];  // 64kB is max possible xattr list size. See "man 7 xattr".
+  ASSERT_EQ(0, fsetxattr(tf.fd, "user.foo", "bar", 4, 0));
+  int fd = open(tf.filename, O_PATH);
+  ASSERT_NE(-1, fd);
+  ssize_t res = flistxattr(fd, buf, sizeof(buf));
+#if defined(__BIONIC__)
+  ASSERT_TRUE(res >= 9);
+  ASSERT_TRUE(static_cast<size_t>(res) <= sizeof(buf));
+  ASSERT_TRUE(memmem(buf, res, "user.foo", 9) != NULL);
+#else
+  ASSERT_EQ(-1, res);
+  ASSERT_EQ(EBADF, errno);
+#endif
+  close(fd);
 }