Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 787 insertions, 0 deletions

diff --git a/modules/libmar/src/mar_read.c b/modules/libmar/src/mar_read.c
new file mode 100644
index 0000000000..679dc258d6
--- /dev/null
+++ b/modules/libmar/src/mar_read.c
@@ -0,0 +1,787 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include <sys/types.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <string.h>
+#include "city.h"
+#include "mar_private.h"
+#include "mar.h"
+#ifdef XP_WIN
+#  define strdup _strdup
+#endif
+
+/* This block must be at most 104 bytes.
+   MAR channel name < 64 bytes, and product version < 32 bytes + 3 NULL
+   terminator bytes. We only check for 96 though because we remove 8
+   bytes above from the additionalBlockSize: We subtract
+   sizeof(additionalBlockSize) and sizeof(additionalBlockID) */
+#define MAXADDITIONALBLOCKSIZE 96
+
+static uint32_t mar_hash_name(const char* name) {
+  return CityHash64(name, strlen(name)) % TABLESIZE;
+}
+
+static int mar_insert_item(MarFile* mar, const char* name, uint32_t namelen,
+                           uint32_t offset, uint32_t length, uint32_t flags) {
+  MarItem *item, *root;
+  uint32_t hash;
+
+  item = (MarItem*)malloc(sizeof(MarItem) + namelen);
+  if (!item) {
+    return -1;
+  }
+  item->next = NULL;
+  item->offset = offset;
+  item->length = length;
+  item->flags = flags;
+  memcpy(item->name, name, namelen + 1);
+
+  hash = mar_hash_name(name);
+
+  root = mar->item_table[hash];
+  if (!root) {
+    mar->item_table[hash] = item;
+  } else {
+    /* append item */
+    while (root->next) root = root->next;
+    root->next = item;
+  }
+  return 0;
+}
+
+static int mar_consume_index(MarFile* mar, char** buf, const char* buf_end) {
+  /*
+   * Each item has the following structure:
+   *   uint32_t offset      (network byte order)
+   *   uint32_t length      (network byte order)
+   *   uint32_t flags       (network byte order)
+   *   char     name[N]     (where N >= 1)
+   *   char     null_byte;
+   */
+  uint32_t offset;
+  uint32_t length;
+  uint32_t flags;
+  const char* name;
+  int namelen;
+
+  if ((buf_end - *buf) < (int)(3 * sizeof(uint32_t) + 2)) {
+    return -1;
+  }
+
+  memcpy(&offset, *buf, sizeof(offset));
+  *buf += sizeof(offset);
+
+  memcpy(&length, *buf, sizeof(length));
+  *buf += sizeof(length);
+
+  memcpy(&flags, *buf, sizeof(flags));
+  *buf += sizeof(flags);
+
+  offset = ntohl(offset);
+  length = ntohl(length);
+  flags = ntohl(flags);
+
+  name = *buf;
+  /* find namelen; must take care not to read beyond buf_end */
+  while (**buf) {
+    /* buf_end points one byte past the end of buf's allocation */
+    if (*buf == (buf_end - 1)) {
+      return -1;
+    }
+    ++(*buf);
+  }
+  namelen = (*buf - name);
+  /* must ensure that namelen is valid */
+  if (namelen < 0) {
+    return -1;
+  }
+  /* consume null byte */
+  if (*buf == buf_end) {
+    return -1;
+  }
+  ++(*buf);
+
+  return mar_insert_item(mar, name, namelen, offset, length, flags);
+}
+
+static int mar_read_index(MarFile* mar) {
+  char id[MAR_ID_SIZE], *buf, *bufptr, *bufend;
+  uint32_t offset_to_index, size_of_index;
+  size_t mar_position = 0;
+
+  /* verify MAR ID */
+  if (mar_read_buffer(mar, id, &mar_position, MAR_ID_SIZE) != 0) {
+    return -1;
+  }
+  if (memcmp(id, MAR_ID, MAR_ID_SIZE) != 0) {
+    return -1;
+  }
+
+  if (mar_read_buffer(mar, &offset_to_index, &mar_position, sizeof(uint32_t)) !=
+      0) {
+    return -1;
+  }
+  offset_to_index = ntohl(offset_to_index);
+
+  mar_position = 0;
+  if (mar_buffer_seek(mar, &mar_position, offset_to_index) != 0) {
+    return -1;
+  }
+  if (mar_read_buffer(mar, &size_of_index, &mar_position, sizeof(uint32_t)) !=
+      0) {
+    return -1;
+  }
+  size_of_index = ntohl(size_of_index);
+
+  buf = (char*)malloc(size_of_index);
+  if (!buf) {
+    return -1;
+  }
+  if (mar_read_buffer(mar, buf, &mar_position, size_of_index) != 0) {
+    free(buf);
+    return -1;
+  }
+
+  bufptr = buf;
+  bufend = buf + size_of_index;
+  while (bufptr < bufend && mar_consume_index(mar, &bufptr, bufend) == 0)
+    ;
+
+  free(buf);
+  return (bufptr == bufend) ? 0 : -1;
+}
+
+/**
+ * Adds an offset and length to the MarFile's index_list
+ * @param mar     The MarFile that owns this offset length pair
+ * @param offset  The byte offset in the archive to be marked as processed
+ * @param length  The length corresponding to this byte offset
+ * @return int    1 on success, 0 if offset has been previously processed
+ *                -1 if unable to allocate space for the SeenIndexes
+ */
+static int mar_insert_offset(MarFile* mar, uint32_t offset, uint32_t length) {
+  /* Ignore files with no length */
+  if (length == 0) {
+    return 1;
+  }
+
+  SeenIndex* index = (SeenIndex*)malloc(sizeof(SeenIndex));
+  if (!index) {
+    return -1;
+  }
+  index->next = NULL;
+  index->offset = offset;
+  index->length = length;
+  uint32_t index_end = index->offset + index->length - 1;
+
+  /* If this is our first index store it at the front */
+  if (mar->index_list == NULL) {
+    mar->index_list = index;
+    return 1;
+  }
+
+  /* Search for matching indexes in the list of those previously visited */
+  SeenIndex* previous;
+  SeenIndex* current = mar->index_list;
+  while (current != NULL) {
+    uint32_t current_end = current->offset + current->length - 1;
+
+    /* If index has collided with the front or end of current or if current has
+       collided with the front or end of index return false */
+    if ((index->offset >= current->offset && index->offset <= current_end) ||
+        (index_end >= current->offset && index_end <= current_end) ||
+        (current->offset >= index->offset && current->offset <= index_end) ||
+        (current_end >= index->offset && current_end <= index_end)) {
+      free(index);
+      return 0;
+    }
+
+    /* else move to the next in the list */
+    previous = current;
+    current = current->next;
+  }
+
+  /* These indexes are valid, track them */
+  previous->next = index;
+  return 1;
+}
+
+/**
+ * Internal shared code for mar_open and mar_wopen.
+ * Reads the entire MAR into memory. Fails if it is bigger than
+ * MAX_SIZE_OF_MAR_FILE bytes.
+ */
+static MarReadResult mar_fpopen(FILE* fp, MarFile** out_mar) {
+  *out_mar = NULL;
+  MarFile* mar;
+
+  mar = (MarFile*)malloc(sizeof(*mar));
+  if (!mar) {
+    return MAR_MEM_ERROR;
+  }
+
+  off_t buffer_size = -1;
+  if (fseeko(fp, 0, SEEK_END) == 0) {
+    buffer_size = ftello(fp);
+  }
+  rewind(fp);
+  if (buffer_size < 0) {
+    fprintf(stderr, "Warning: MAR size could not be determined\n");
+    buffer_size = MAX_SIZE_OF_MAR_FILE;
+  }
+  if (buffer_size > MAX_SIZE_OF_MAR_FILE) {
+    fprintf(stderr, "ERROR: MAR exceeds maximum size (%lli)\n",
+            (long long int)buffer_size);
+    free(mar);
+    return MAR_FILE_TOO_BIG_ERROR;
+  }
+
+  mar->buffer = malloc(buffer_size);
+  if (!mar->buffer) {
+    fprintf(stderr, "ERROR: MAR buffer could not be allocated\n");
+    free(mar);
+    return MAR_MEM_ERROR;
+  }
+  mar->data_len = fread(mar->buffer, 1, buffer_size, fp);
+  if (fgetc(fp) != EOF) {
+    fprintf(stderr, "ERROR: File is larger than buffer (%lli)\n",
+            (long long int)buffer_size);
+    free(mar->buffer);
+    free(mar);
+    return MAR_IO_ERROR;
+  }
+  if (ferror(fp)) {
+    fprintf(stderr, "ERROR: Failed to read MAR\n");
+    free(mar->buffer);
+    free(mar);
+    return MAR_IO_ERROR;
+  }
+
+  mar->item_table_is_valid = 0;
+  memset(mar->item_table, 0, sizeof(mar->item_table));
+  mar->index_list = NULL;
+
+  *out_mar = mar;
+  return MAR_READ_SUCCESS;
+}
+
+MarReadResult mar_open(const char* path, MarFile** out_mar) {
+  *out_mar = NULL;
+
+  FILE* fp;
+
+  fp = fopen(path, "rb");
+  if (!fp) {
+    fprintf(stderr, "ERROR: could not open file in mar_open()\n");
+    perror(path);
+    return MAR_IO_ERROR;
+  }
+
+  MarReadResult result = mar_fpopen(fp, out_mar);
+  fclose(fp);
+  return result;
+}
+
+#ifdef XP_WIN
+MarReadResult mar_wopen(const wchar_t* path, MarFile** out_mar) {
+  *out_mar = NULL;
+
+  FILE* fp;
+
+  _wfopen_s(&fp, path, L"rb");
+  if (!fp) {
+    fprintf(stderr, "ERROR: could not open file in mar_wopen()\n");
+    _wperror(path);
+    return MAR_IO_ERROR;
+  }
+
+  MarReadResult result = mar_fpopen(fp, out_mar);
+  fclose(fp);
+  return result;
+}
+#endif
+
+void mar_close(MarFile* mar) {
+  MarItem* item;
+  SeenIndex* index;
+  int i;
+
+  free(mar->buffer);
+
+  for (i = 0; i < TABLESIZE; ++i) {
+    item = mar->item_table[i];
+    while (item) {
+      MarItem* temp = item;
+      item = item->next;
+      free(temp);
+    }
+  }
+
+  while (mar->index_list != NULL) {
+    index = mar->index_list;
+    mar->index_list = index->next;
+    free(index);
+  }
+
+  free(mar);
+}
+
+int mar_read_buffer(MarFile* mar, void* dest, size_t* position, size_t size) {
+  // size may be provided by the MAR, which we may not have finished validating
+  // the signature on yet. Make sure not to trust it in a way that could
+  // cause an overflow.
+  if (size > mar->data_len) {
+    return -1;
+  }
+  if (*position > mar->data_len - size) {
+    return -1;
+  }
+  memcpy(dest, mar->buffer + *position, size);
+  *position += size;
+  return 0;
+}
+
+int mar_read_buffer_max(MarFile* mar, void* dest, size_t* position,
+                        size_t size) {
+  // size may be provided by the MAR, which we may not have finished validating
+  // the signature on yet. Make sure not to trust it in a way that could
+  // cause an overflow.
+  if (mar->data_len <= *position) {
+    return 0;
+  }
+  size_t read_count = mar->data_len - *position;
+  if (read_count > size) {
+    read_count = size;
+  }
+  memcpy(dest, mar->buffer + *position, read_count);
+  *position += read_count;
+  return read_count;
+}
+
+int mar_buffer_seek(MarFile* mar, size_t* position, size_t distance) {
+  // distance may be provided by the MAR, which we may not have finished
+  // validating the signature on yet. Make sure not to trust it in a way that
+  // could cause an overflow.
+  if (distance > mar->data_len) {
+    return -1;
+  }
+  if (*position > mar->data_len - distance) {
+    return -1;
+  }
+  *position += distance;
+  return 0;
+}
+
+/**
+ * Determines the MAR file information.
+ *
+ * @param mar                    An open MAR file.
+ * @param mar_position           The current position in the MAR.
+ *                               Its value will be updated to the current
+ *                               position in the MAR after the function exits.
+ *                               Since its initial value will never actually be
+ *                               used, this is effectively an outparam.
+ * @param hasSignatureBlock      Optional out parameter specifying if the MAR
+ *                               file has a signature block or not.
+ * @param numSignatures          Optional out parameter for storing the number
+ *                               of signatures in the MAR file.
+ * @param hasAdditionalBlocks    Optional out parameter specifying if the MAR
+ *                               file has additional blocks or not.
+ * @param offsetAdditionalBlocks Optional out parameter for the offset to the
+ *                               first additional block. Value is only valid if
+ *                               hasAdditionalBlocks is not equal to 0.
+ * @param numAdditionalBlocks    Optional out parameter for the number of
+ *                               additional blocks.  Value is only valid if
+ *                               hasAdditionalBlocks is not equal to 0.
+ * @return 0 on success and non-zero on failure.
+ */
+int get_open_mar_file_info(MarFile* mar, size_t* mar_position,
+                           int* hasSignatureBlock, uint32_t* numSignatures,
+                           int* hasAdditionalBlocks,
+                           uint32_t* offsetAdditionalBlocks,
+                           uint32_t* numAdditionalBlocks) {
+  uint32_t offsetToIndex, offsetToContent, signatureCount, signatureLen, i;
+
+  /* One of hasSignatureBlock or hasAdditionalBlocks must be non NULL */
+  if (!hasSignatureBlock && !hasAdditionalBlocks) {
+    return -1;
+  }
+
+  /* Skip to the start of the offset index */
+  *mar_position = 0;
+  if (mar_buffer_seek(mar, mar_position, MAR_ID_SIZE) != 0) {
+    return -1;
+  }
+
+  /* Read the offset to the index. */
+  if (mar_read_buffer(mar, &offsetToIndex, mar_position,
+                      sizeof(offsetToIndex)) != 0) {
+    return -1;
+  }
+  offsetToIndex = ntohl(offsetToIndex);
+
+  if (numSignatures) {
+    /* Skip past the MAR file size field */
+    if (mar_buffer_seek(mar, mar_position, sizeof(uint64_t)) != 0) {
+      return -1;
+    }
+
+    /* Read the number of signatures field */
+    if (mar_read_buffer(mar, numSignatures, mar_position,
+                        sizeof(*numSignatures)) != 0) {
+      return -1;
+    }
+    *numSignatures = ntohl(*numSignatures);
+  }
+
+  /* Skip to the first index entry past the index size field
+     We do it in 2 calls because offsetToIndex + sizeof(uint32_t)
+     could overflow in theory. */
+  *mar_position = 0;
+  if (mar_buffer_seek(mar, mar_position, offsetToIndex) != 0) {
+    return -1;
+  }
+
+  if (mar_buffer_seek(mar, mar_position, sizeof(uint32_t)) != 0) {
+    return -1;
+  }
+
+  /* Read the first offset to content field. */
+  if (mar_read_buffer(mar, &offsetToContent, mar_position,
+                      sizeof(offsetToContent)) != 0) {
+    return -1;
+  }
+  offsetToContent = ntohl(offsetToContent);
+
+  /* Check if we have a new or old MAR file */
+  if (hasSignatureBlock) {
+    if (offsetToContent == MAR_ID_SIZE + sizeof(uint32_t)) {
+      *hasSignatureBlock = 0;
+    } else {
+      *hasSignatureBlock = 1;
+    }
+  }
+
+  /* If the caller doesn't care about the product info block
+     value, then just return */
+  if (!hasAdditionalBlocks) {
+    return 0;
+  }
+
+  /* Skip to the start of the signature block */
+  *mar_position = 0;
+  if (mar_buffer_seek(mar, mar_position, SIGNATURE_BLOCK_OFFSET) != 0) {
+    return -1;
+  }
+
+  /* Get the number of signatures */
+  if (mar_read_buffer(mar, &signatureCount, mar_position,
+                      sizeof(signatureCount)) != 0) {
+    return -1;
+  }
+  signatureCount = ntohl(signatureCount);
+
+  /* Check that we have less than the max amount of signatures so we don't
+     waste too much of either updater's or signmar's time. */
+  if (signatureCount > MAX_SIGNATURES) {
+    return -1;
+  }
+
+  /* Skip past the whole signature block */
+  for (i = 0; i < signatureCount; i++) {
+    /* Skip past the signature algorithm ID */
+    if (mar_buffer_seek(mar, mar_position, sizeof(uint32_t)) != 0) {
+      return -1;
+    }
+
+    /* Read the signature length and skip past the signature */
+    if (mar_read_buffer(mar, &signatureLen, mar_position, sizeof(uint32_t)) !=
+        0) {
+      return -1;
+    }
+    signatureLen = ntohl(signatureLen);
+    if (mar_buffer_seek(mar, mar_position, signatureLen) != 0) {
+      return -1;
+    }
+  }
+
+  if (*mar_position <= (size_t)INT64_MAX &&
+      (int64_t)mar_position == (int64_t)offsetToContent) {
+    *hasAdditionalBlocks = 0;
+  } else {
+    if (numAdditionalBlocks) {
+      /* We have an additional block, so read in the number of additional blocks
+         and set the offset. */
+      *hasAdditionalBlocks = 1;
+      if (mar_read_buffer(mar, numAdditionalBlocks, mar_position,
+                          sizeof(uint32_t)) != 0) {
+        return -1;
+      }
+      *numAdditionalBlocks = ntohl(*numAdditionalBlocks);
+      if (offsetAdditionalBlocks) {
+        if (*mar_position > (size_t)UINT32_MAX) {
+          return -1;
+        }
+        *offsetAdditionalBlocks = (uint32_t)*mar_position;
+      }
+    } else if (offsetAdditionalBlocks) {
+      /* numAdditionalBlocks is not specified but offsetAdditionalBlocks
+         is, so fill it! */
+      if (mar_buffer_seek(mar, mar_position, sizeof(uint32_t)) != 0) {
+        return -1;
+      }
+      if (*mar_position > (size_t)UINT32_MAX) {
+        return -1;
+      }
+      *offsetAdditionalBlocks = (uint32_t)*mar_position;
+    }
+  }
+
+  return 0;
+}
+
+/**
+ * Reads the product info block from the MAR file's additional block section.
+ * The caller is responsible for freeing the fields in infoBlock
+ * if the return is successful.
+ *
+ * @param infoBlock Out parameter for where to store the result to
+ * @return 0 on success, -1 on failure
+ */
+int read_product_info_block(char* path,
+                            struct ProductInformationBlock* infoBlock) {
+  int rv;
+  MarFile* mar;
+  MarReadResult result = mar_open(path, &mar);
+  if (result != MAR_READ_SUCCESS) {
+    fprintf(stderr,
+            "ERROR: could not open file in read_product_info_block()\n");
+    return -1;
+  }
+  rv = mar_read_product_info_block(mar, infoBlock);
+  mar_close(mar);
+  return rv;
+}
+
+/**
+ * Reads the product info block from the MAR file's additional block section.
+ * The caller is responsible for freeing the fields in infoBlock
+ * if the return is successful.
+ *
+ * @param infoBlock Out parameter for where to store the result to
+ * @return 0 on success, -1 on failure
+ */
+int mar_read_product_info_block(MarFile* mar,
+                                struct ProductInformationBlock* infoBlock) {
+  uint32_t offsetAdditionalBlocks, numAdditionalBlocks, additionalBlockSize,
+      additionalBlockID;
+  int hasAdditionalBlocks;
+  size_t mar_position = 0;
+
+  /* The buffer size is 97 bytes because the MAR channel name < 64 bytes, and
+     product version < 32 bytes + 3 NULL terminator bytes. */
+  char buf[MAXADDITIONALBLOCKSIZE + 1] = {'\0'};
+  if (get_open_mar_file_info(mar, &mar_position, NULL, NULL,
+                             &hasAdditionalBlocks, &offsetAdditionalBlocks,
+                             &numAdditionalBlocks) != 0) {
+    return -1;
+  }
+
+  /* We only have the one additional block type and only one is expected to be
+     in a MAR file so check if any exist and process the first found */
+  if (numAdditionalBlocks > 0) {
+    /* Read the additional block size */
+    if (mar_read_buffer(mar, &additionalBlockSize, &mar_position,
+                        sizeof(additionalBlockSize)) != 0) {
+      return -1;
+    }
+    additionalBlockSize = ntohl(additionalBlockSize) -
+                          sizeof(additionalBlockSize) -
+                          sizeof(additionalBlockID);
+
+    /* Additional Block sizes should only be 96 bytes long */
+    if (additionalBlockSize > MAXADDITIONALBLOCKSIZE) {
+      return -1;
+    }
+
+    /* Read the additional block ID */
+    if (mar_read_buffer(mar, &additionalBlockID, &mar_position,
+                        sizeof(additionalBlockID)) != 0) {
+      return -1;
+    }
+    additionalBlockID = ntohl(additionalBlockID);
+
+    if (PRODUCT_INFO_BLOCK_ID == additionalBlockID) {
+      const char* location;
+      int len;
+
+      if (mar_read_buffer(mar, buf, &mar_position, additionalBlockSize) != 0) {
+        return -1;
+      }
+
+      /* Extract the MAR channel name from the buffer.  For now we
+         point to the stack allocated buffer but we strdup this
+         if we are within bounds of each field's max length. */
+      location = buf;
+      len = strlen(location);
+      infoBlock->MARChannelID = location;
+      location += len + 1;
+      if (len >= 64) {
+        infoBlock->MARChannelID = NULL;
+        return -1;
+      }
+
+      /* Extract the version from the buffer */
+      len = strlen(location);
+      infoBlock->productVersion = location;
+      if (len >= 32) {
+        infoBlock->MARChannelID = NULL;
+        infoBlock->productVersion = NULL;
+        return -1;
+      }
+      infoBlock->MARChannelID = strdup(infoBlock->MARChannelID);
+      infoBlock->productVersion = strdup(infoBlock->productVersion);
+      return 0;
+    } else {
+      /* This is not the additional block you're looking for. Move along. */
+      if (mar_buffer_seek(mar, &mar_position, additionalBlockSize) != 0) {
+        return -1;
+      }
+    }
+  }
+
+  /* If we had a product info block we would have already returned */
+  return -1;
+}
+
+const MarItem* mar_find_item(MarFile* mar, const char* name) {
+  uint32_t hash;
+  const MarItem* item;
+
+  if (!mar->item_table_is_valid) {
+    if (mar_read_index(mar)) {
+      return NULL;
+    } else {
+      mar->item_table_is_valid = 1;
+    }
+  }
+
+  hash = mar_hash_name(name);
+
+  item = mar->item_table[hash];
+  while (item && strcmp(item->name, name) != 0) {
+    item = item->next;
+  }
+
+  /* If this is the first time seeing this item's indexes, return it */
+  if (mar_insert_offset(mar, item->offset, item->length) == 1) {
+    return item;
+  } else {
+    fprintf(stderr, "ERROR: file content collision in mar_find_item()\n");
+    return NULL;
+  }
+}
+
+int mar_enum_items(MarFile* mar, MarItemCallback callback, void* closure) {
+  MarItem* item;
+  int i, rv;
+
+  if (!mar->item_table_is_valid) {
+    if (mar_read_index(mar)) {
+      return -1;
+    } else {
+      mar->item_table_is_valid = 1;
+    }
+  }
+
+  for (i = 0; i < TABLESIZE; ++i) {
+    item = mar->item_table[i];
+    while (item) {
+      /* if this is the first time seeing this item's indexes, process it */
+      if (mar_insert_offset(mar, item->offset, item->length) == 1) {
+        rv = callback(mar, item, closure);
+        if (rv) {
+          return rv;
+        }
+      } else {
+        fprintf(stderr, "ERROR: file content collision in mar_enum_items()\n");
+        return 1;
+      }
+      item = item->next;
+    }
+  }
+
+  return 0;
+}
+
+int mar_read(MarFile* mar, const MarItem* item, int offset, uint8_t* buf,
+             int bufsize) {
+  int nr;
+  size_t mar_position = 0;
+
+  if (offset == (int)item->length) {
+    return 0;
+  }
+  if (offset > (int)item->length) {
+    return -1;
+  }
+
+  nr = item->length - offset;
+  if (nr > bufsize) {
+    nr = bufsize;
+  }
+
+  // Avoid adding item->offset and offset directly, just in case of overflow.
+  if (mar_buffer_seek(mar, &mar_position, item->offset)) {
+    return -1;
+  }
+  if (mar_buffer_seek(mar, &mar_position, offset)) {
+    return -1;
+  }
+
+  return mar_read_buffer_max(mar, buf, &mar_position, nr);
+}
+
+/**
+ * Determines the MAR file information.
+ *
+ * @param path                   The path of the MAR file to check.
+ * @param hasSignatureBlock      Optional out parameter specifying if the MAR
+ *                               file has a signature block or not.
+ * @param numSignatures          Optional out parameter for storing the number
+ *                               of signatures in the MAR file.
+ * @param hasAdditionalBlocks    Optional out parameter specifying if the MAR
+ *                               file has additional blocks or not.
+ * @param offsetAdditionalBlocks Optional out parameter for the offset to the
+ *                               first additional block. Value is only valid if
+ *                               hasAdditionalBlocks is not equal to 0.
+ * @param numAdditionalBlocks    Optional out parameter for the number of
+ *                               additional blocks.  Value is only valid if
+ *                               has_additional_blocks is not equal to 0.
+ * @return 0 on success and non-zero on failure.
+ */
+int get_mar_file_info(const char* path, int* hasSignatureBlock,
+                      uint32_t* numSignatures, int* hasAdditionalBlocks,
+                      uint32_t* offsetAdditionalBlocks,
+                      uint32_t* numAdditionalBlocks) {
+  int rv;
+  MarFile* mar;
+  size_t mar_position = 0;
+  MarReadResult result = mar_open(path, &mar);
+  if (result != MAR_READ_SUCCESS) {
+    fprintf(stderr, "ERROR: could not read file in get_mar_file_info()\n");
+    return -1;
+  }
+
+  rv = get_open_mar_file_info(mar, &mar_position, hasSignatureBlock,
+                              numSignatures, hasAdditionalBlocks,
+                              offsetAdditionalBlocks, numAdditionalBlocks);
+
+  mar_close(mar);
+  return rv;
+}