Hide statfs/fstatfs' ST_VALID flag from userspace.

Spotted while debugging the strace 4.10 upgrade.

Change-Id: I1af1be9c9440151f55f74a835e1df71529b0e4fe

1 files changed, 29 insertions, 5 deletions

diff --git a/libc/bionic/statvfs.cpp b/libc/bionic/statvfs.cpp
index f1e2833..39ffb64 100644
--- a/libc/bionic/statvfs.cpp
+++ b/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;
   }