Hide statfs/fstatfs' ST_VALID flag from userspace.

Spotted while debugging the strace 4.10 upgrade.

Change-Id: I1af1be9c9440151f55f74a835e1df71529b0e4fe

libc/SYSCALLS.TXT

@@ -174,9 +174,9 @@ int __fadvise64:fadvise64_64(int, off64_t, off64_t, int) x86
 int __fadvise64:fadvise64(int, off64_t, off64_t, int) arm64,mips,mips64,x86_64
 
 int __fstatfs64:fstatfs64(int, size_t, struct statfs*)  arm,mips,x86
-int fstatfs64|fstatfs:fstatfs(int, struct statfs*)  arm64,mips64,x86_64
+int __fstatfs:fstatfs(int, struct statfs*)  arm64,mips64,x86_64
 int __statfs64:statfs64(const char*, size_t, struct statfs*)  arm,mips,x86
-int statfs64|statfs:statfs(const char*, struct statfs*)  arm64,mips64,x86_64
+int __statfs:statfs(const char*, struct statfs*)  arm64,mips64,x86_64
 
 int     fstat64|fstat:fstat64(int, struct stat*)    arm,mips,x86
 int     fstat64|fstat:fstat(int, struct stat*)    arm64,x86_64

libc/arch-arm64/syscalls/__fstatfs.S

@@ -2,7 +2,7 @@
 
 #include <private/bionic_asm.h>
 
-ENTRY(fstatfs64)
+ENTRY(__fstatfs)
     mov     x8, __NR_fstatfs
     svc     #0
 
@@ -11,7 +11,5 @@ ENTRY(fstatfs64)
     b.hi    __set_errno_internal
 
     ret
-END(fstatfs64)
-
-    .globl fstatfs
-    .equ fstatfs, fstatfs64
+END(__fstatfs)
+.hidden __fstatfs

libc/arch-arm64/syscalls/__statfs.S

@@ -2,7 +2,7 @@
 
 #include <private/bionic_asm.h>
 
-ENTRY(statfs64)
+ENTRY(__statfs)
     mov     x8, __NR_statfs
     svc     #0
 
@@ -11,7 +11,5 @@ ENTRY(statfs64)
     b.hi    __set_errno_internal
 
     ret
-END(statfs64)
-
-    .globl statfs
-    .equ statfs, statfs64
+END(__statfs)
+.hidden __statfs

libc/arch-mips64/syscalls/__fstatfs.S

@@ -2,7 +2,7 @@
 
 #include <private/bionic_asm.h>
 
-ENTRY(fstatfs64)
+ENTRY(__fstatfs)
     .set push
     .set noreorder
     li v0, __NR_fstatfs
@@ -22,7 +22,5 @@ ENTRY(fstatfs64)
     j t9
     move ra, t0
     .set pop
-END(fstatfs64)
-
-    .globl fstatfs
-    .equ fstatfs, fstatfs64
+END(__fstatfs)
+.hidden __fstatfs

libc/arch-mips64/syscalls/__statfs.S

@@ -2,7 +2,7 @@
 
 #include <private/bionic_asm.h>
 
-ENTRY(statfs64)
+ENTRY(__statfs)
     .set push
     .set noreorder
     li v0, __NR_statfs
@@ -22,7 +22,5 @@ ENTRY(statfs64)
     j t9
     move ra, t0
     .set pop
-END(statfs64)
-
-    .globl statfs
-    .equ statfs, statfs64
+END(__statfs)
+.hidden __statfs

libc/arch-x86_64/syscalls/__fstatfs.S

@@ -2,7 +2,7 @@
 
 #include <private/bionic_asm.h>
 
-ENTRY(fstatfs64)
+ENTRY(__fstatfs)
     movl    $__NR_fstatfs, %eax
     syscall
     cmpq    $-MAX_ERRNO, %rax
@@ -12,7 +12,5 @@ ENTRY(fstatfs64)
     call    __set_errno_internal
 1:
     ret
-END(fstatfs64)
-
-    .globl fstatfs
-    .equ fstatfs, fstatfs64
+END(__fstatfs)
+.hidden __fstatfs

libc/arch-x86_64/syscalls/__statfs.S

@@ -2,7 +2,7 @@
 
 #include <private/bionic_asm.h>
 
-ENTRY(statfs64)
+ENTRY(__statfs)
     movl    $__NR_statfs, %eax
     syscall
     cmpq    $-MAX_ERRNO, %rax
@@ -12,7 +12,5 @@ ENTRY(statfs64)
     call    __set_errno_internal
 1:
     ret
-END(statfs64)
-
-    .globl statfs
-    .equ statfs, statfs64
+END(__statfs)
+.hidden __statfs

libc/bionic/legacy_32_bit_support.cpp

@@ -40,9 +40,7 @@
 
 // System calls we need.
 extern "C" int __fcntl64(int, int, void*);
-extern "C" int __fstatfs64(int, size_t, struct statfs*);
 extern "C" int __llseek(int, unsigned long, unsigned long, off64_t*, int);
-extern "C" int __statfs64(const char*, size_t, struct statfs*);
 
 // For fcntl we use the fcntl64 system call to signal that we're using struct flock64.
 int fcntl(int fd, int cmd, ...) {
@@ -55,18 +53,6 @@ int fcntl(int fd, int cmd, ...) {
   return __fcntl64(fd, cmd, arg);
 }
 
-// For fstatfs we need to add the extra argument giving the kernel the size of the buffer.
-int fstatfs(int fd, struct statfs* stat) {
-  return __fstatfs64(fd, sizeof(*stat), stat);
-}
-__strong_alias(fstatfs64, fstatfs);
-
-// For statfs we need to add the extra argument giving the kernel the size of the buffer.
-int statfs(const char* path, struct statfs* stat) {
-  return __statfs64(path, sizeof(*stat), stat);
-}
-__strong_alias(statfs64, statfs);
-
 // For lseek64 we need to use the llseek system call which splits the off64_t in two and
 // returns the off64_t result via a pointer because 32-bit kernels can't return 64-bit results.
 off64_t lseek64(int fd, off64_t off, int whence) {

libc/bionic/statvfs.cpp

@@ -21,13 +21,17 @@
 // Paper over the fact that 32-bit kernels use fstatfs64/statfs64 with an extra argument,
 // but 64-bit kernels don't have the "64" bit suffix or the extra size_t argument.
 #if __LP64__
-#  define __fstatfs64(fd,size,buf) fstatfs(fd,buf)
-#  define __statfs64(path,size,buf) statfs(path,buf)
+extern "C" int __fstatfs(int, struct statfs*);
+extern "C" int __statfs(const char*, struct statfs*);
+#  define __fstatfs64(fd,size,buf) __fstatfs(fd,buf)
+#  define __statfs64(path,size,buf) __statfs(path,buf)
 #else
 extern "C" int __fstatfs64(int, size_t, struct statfs*);
 extern "C" int __statfs64(const char*, size_t, struct statfs*);
 #endif
 
+// The kernel sets a private ST_VALID flag to signal to the C library whether the
+// f_flags field is valid. This flag should not be exposed to users of the C library.
 #define ST_VALID 0x0020
 
 static void __statfs_to_statvfs(const struct statfs& in, struct statvfs* out) {
@@ -40,13 +44,33 @@ static void __statfs_to_statvfs(const struct statfs& in, struct statvfs* out) {
   out->f_ffree = in.f_ffree;
   out->f_favail = in.f_ffree;
   out->f_fsid = in.f_fsid.__val[0] | (static_cast<uint64_t>(in.f_fsid.__val[1]) << 32);
-  out->f_flag = in.f_flags & ~ST_VALID;
+  out->f_flag = in.f_flags;
   out->f_namemax = in.f_namelen;
 }
 
+int fstatfs(int fd, struct statfs* result) {
+  int rc = __fstatfs64(fd, sizeof(*result), result);
+  if (rc != 0) {
+    return rc;
+  }
+  result->f_flags &= ~ST_VALID;
+  return 0;
+}
+__strong_alias(fstatfs64, fstatfs);
+
+int statfs(const char* path, struct statfs* result) {
+  int rc = __statfs64(path, sizeof(*result), result);
+  if (rc != 0) {
+    return rc;
+  }
+  result->f_flags &= ~ST_VALID;
+  return 0;
+}
+__strong_alias(statfs64, statfs);
+
 int statvfs(const char* path, struct statvfs* result) {
   struct statfs tmp;
-  int rc = __statfs64(path, sizeof(tmp), &tmp);
+  int rc = statfs(path, &tmp);
   if (rc != 0) {
     return rc;
   }
@@ -57,7 +81,7 @@ __strong_alias(statvfs64, statvfs);
 
 int fstatvfs(int fd, struct statvfs* result) {
   struct statfs tmp;
-  int rc = __fstatfs64(fd, sizeof(tmp), &tmp);
+  int rc = fstatfs(fd, &tmp);
   if (rc != 0) {
     return rc;
   }

tests/sys_statvfs_test.cpp

@@ -30,6 +30,11 @@ template <typename StatVfsT> void Check(StatVfsT& sb) {
   EXPECT_EQ(0U, sb.f_ffree);
   EXPECT_EQ(0U, sb.f_fsid);
   EXPECT_EQ(255U, sb.f_namemax);
+
+  // The kernel sets a private bit to indicate that f_flags is valid.
+  // This flag is not supposed to be exposed to libc clients.
+  static const uint32_t ST_VALID = 0x0020;
+  EXPECT_TRUE((sb.f_flag & ST_VALID) == 0) << sb.f_flag;
 }
 
 TEST(sys_statvfs, statvfs) {
@@ -51,6 +56,7 @@ TEST(sys_statvfs, fstatvfs) {
   close(fd);
   Check(sb);
 }
+
 TEST(sys_statvfs, fstatvfs64) {
   struct statvfs64 sb;
   int fd = open("/proc", O_RDONLY);

tests/sys_vfs_test.cpp

@@ -31,6 +31,11 @@ template <typename StatFsT> void Check(StatFsT& sb) {
   EXPECT_EQ(0, sb.f_fsid.__val[0]);
   EXPECT_EQ(0, sb.f_fsid.__val[1]);
   EXPECT_EQ(255, static_cast<int>(sb.f_namelen));
+
+  // The kernel sets a private bit to indicate that f_flags is valid.
+  // This flag is not supposed to be exposed to libc clients.
+  static const uint32_t ST_VALID = 0x0020;
+  EXPECT_TRUE((sb.f_flags & ST_VALID) == 0) << sb.f_flags;
 }
 
 TEST(sys_vfs, statfs) {
@@ -52,6 +57,7 @@ TEST(sys_vfs, fstatfs) {
   close(fd);
   Check(sb);
 }
+
 TEST(sys_vfs, fstatfs64) {
   struct statfs64 sb;
   int fd = open("/proc", O_RDONLY);