Revert "Add ParseFstabFromString(), remove ReadFstabFromFp()"

Revert submission 1890098

Reason for revert: Breaks tests, b/206740783
Reverted Changes:
I71190c735:Add ParseFstabFromString(), remove ReadFstabFromFp...
Ic1dd0eb97:Replace strtok_r() with C++-style android::base::T...

Change-Id: I1ded0217670a9bf3f2485120ee0dddf3e854a6fb

fs_mgr/fs_mgr_fstab.cpp

@@ -525,23 +525,34 @@ bool EraseFstabEntry(Fstab* fstab, const std::string& mount_point) {
 
 }  // namespace
 
-bool ParseFstabFromString(const std::string& fstab_str, bool proc_mounts, Fstab* fstab_out) {
+bool ReadFstabFromFp(FILE* fstab_file, bool proc_mounts, Fstab* fstab_out) {
     const int expected_fields = proc_mounts ? 4 : 5;
-
+    ssize_t len;
+    size_t alloc_len = 0;
+    char *line = NULL;
+    char* p;
     Fstab fstab;
 
-    for (const auto& line : android::base::Split(fstab_str, "\n")) {
-        auto fields = android::base::Tokenize(line, " \t");
-
-        // Ignore empty lines and comments.
-        if (fields.empty() || android::base::StartsWith(fields.front(), '#')) {
-            continue;
+    while ((len = getline(&line, &alloc_len, fstab_file)) != -1) {
+        /* if the last character is a newline, shorten the string by 1 byte */
+        if (line[len - 1] == '\n') {
+            line[len - 1] = '\0';
         }
 
+        /* Skip any leading whitespace */
+        p = line;
+        while (isspace(*p)) {
+            p++;
+        }
+        /* ignore comments or empty lines */
+        if (*p == '#' || *p == '\0')
+            continue;
+
+        auto fields = android::base::Tokenize(line, " \t");
         if (fields.size() < expected_fields) {
             LERROR << "Error parsing fstab: expected " << expected_fields << " fields, got "
                    << fields.size();
-            return false;
+            goto err;
         }
 
         FstabEntry entry;
@@ -555,7 +566,7 @@ bool ParseFstabFromString(const std::string& fstab_str, bool proc_mounts, Fstab*
         // For /proc/mounts, ignore everything after mnt_freq and mnt_passno
         if (!proc_mounts && !ParseFsMgrFlags(std::move(*it++), &entry)) {
             LERROR << "Error parsing fs_mgr_flags";
-            return false;
+            goto err;
         }
 
         if (entry.fs_mgr_flags.logical) {
@@ -567,17 +578,21 @@ bool ParseFstabFromString(const std::string& fstab_str, bool proc_mounts, Fstab*
 
     if (fstab.empty()) {
         LERROR << "No entries found in fstab";
-        return false;
+        goto err;
     }
 
     /* If an A/B partition, modify block device to be the real block device */
     if (!fs_mgr_update_for_slotselect(&fstab)) {
         LERROR << "Error updating for slotselect";
-        return false;
+        goto err;
     }
-
+    free(line);
     *fstab_out = std::move(fstab);
     return true;
+
+err:
+    free(line);
+    return false;
 }
 
 void TransformFstabForDsu(Fstab* fstab, const std::string& dsu_slot,
@@ -676,18 +691,16 @@ void EnableMandatoryFlags(Fstab* fstab) {
 }
 
 bool ReadFstabFromFile(const std::string& path, Fstab* fstab_out) {
-    const bool is_proc_mounts = (path == "/proc/mounts");
-    // /proc/mounts could be a symlink to /proc/self/mounts.
-    const bool follow_symlinks = is_proc_mounts;
-
-    std::string fstab_str;
-    if (!android::base::ReadFileToString(path, &fstab_str, follow_symlinks)) {
-        PERROR << __FUNCTION__ << "(): failed to read file: '" << path << "'";
+    auto fstab_file = std::unique_ptr<FILE, decltype(&fclose)>{fopen(path.c_str(), "re"), fclose};
+    if (!fstab_file) {
+        PERROR << __FUNCTION__ << "(): cannot open file: '" << path << "'";
         return false;
     }
 
+    bool is_proc_mounts = path == "/proc/mounts";
+
     Fstab fstab;
-    if (!ParseFstabFromString(fstab_str, is_proc_mounts, &fstab)) {
+    if (!ReadFstabFromFp(fstab_file.get(), is_proc_mounts, &fstab)) {
         LERROR << __FUNCTION__ << "(): failed to load fstab from : '" << path << "'";
         return false;
     }
@@ -734,7 +747,15 @@ bool ReadFstabFromDt(Fstab* fstab, bool verbose) {
         return false;
     }
 
-    if (!ParseFstabFromString(fstab_buf, /* proc_mounts = */ false, fstab)) {
+    std::unique_ptr<FILE, decltype(&fclose)> fstab_file(
+        fmemopen(static_cast<void*>(const_cast<char*>(fstab_buf.c_str())),
+                 fstab_buf.length(), "r"), fclose);
+    if (!fstab_file) {
+        if (verbose) PERROR << __FUNCTION__ << "(): failed to create a file stream for fstab dt";
+        return false;
+    }
+
+    if (!ReadFstabFromFp(fstab_file.get(), false, fstab)) {
         if (verbose) {
             LERROR << __FUNCTION__ << "(): failed to load fstab from kernel:" << std::endl
                    << fstab_buf;

fs_mgr/fuzz/fs_mgr_fstab_fuzzer.cpp

@@ -19,8 +19,12 @@
 #include <fstab/fstab.h>
 
 extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
-    std::string make_fstab_str(reinterpret_cast<const char*>(data), size);
+    std::unique_ptr<FILE, decltype(&fclose)> fstab_file(
+            fmemopen(static_cast<void*>(const_cast<uint8_t*>(data)), size, "r"), fclose);
+    if (fstab_file == nullptr) {
+        return 0;
+    }
     android::fs_mgr::Fstab fstab;
-    android::fs_mgr::ParseFstabFromString(make_fstab_str, /* proc_mounts = */ false, &fstab);
+    android::fs_mgr::ReadFstabFromFp(fstab_file.get(), /* proc_mounts= */ false, &fstab);
     return 0;
 }

fs_mgr/include_fstab/fstab/fstab.h

@@ -94,8 +94,8 @@ struct FstabEntry {
 // Unless explicitly requested, a lookup on mount point should always return the 1st one.
 using Fstab = std::vector<FstabEntry>;
 
-// Exported for testability. Regular users should use ReadFstabFromFile().
-bool ParseFstabFromString(const std::string& fstab_str, bool proc_mounts, Fstab* fstab_out);
+// Exported for testability. Regular users should use ReadFstabFromfile().
+bool ReadFstabFromFp(FILE* fstab_file, bool proc_mounts, Fstab* fstab_out);
 
 bool ReadFstabFromFile(const std::string& path, Fstab* fstab);
 bool ReadFstabFromDt(Fstab* fstab, bool verbose = true);