Add microtar library (for use by M3K bootloader)

This is an MIT-licensed library for reading and writing v7 format
tar files. The version here is my fork, which fixes security issues
in the original code (it hasn't been updated in 4 years, probably
abandoned by the author).

Change-Id: I86d41423dacc46e9fa0514b4fc7386a96c216e86

lib/microtar/src/microtar.c

@@ -0,0 +1,403 @@
+/*
+ * Copyright (c) 2017 rxi
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#include <stdlib.h>
+#include <stddef.h>
+#include <limits.h>
+#include <string.h>
+
+#include "microtar.h"
+
+#ifdef ROCKBOX
+/* Rockbox lacks strncpy in its libc */
+static char* strncpy(char* dest, const char* src, size_t n) {
+    size_t i;
+
+    for(i = 0; i < n && *src; ++i)
+        dest[i] = src[i];
+
+    for(; i < n; ++i)
+        dest[i] = 0;
+
+    return dest;
+}
+#endif
+
+
+static int parse_octal(const char* str, size_t len, unsigned* ret) {
+  unsigned n = 0;
+  while(len-- > 0 && *str != 0) {
+    if(*str < '0' || *str > '9')
+      return MTAR_EOVERFLOW;
+
+    if(n > UINT_MAX/8)
+      return MTAR_EOVERFLOW;
+    else
+      n *= 8;
+
+    char r = *str++ - '0';
+    if(n > UINT_MAX - r)
+      return MTAR_EOVERFLOW;
+    else
+      n += r;
+  }
+
+  *ret = n;
+  return MTAR_ESUCCESS;
+}
+
+
+static int print_octal(char* str, size_t len, unsigned value) {
+  /* move backwards over the output string */
+  char* ptr = str + len - 1;
+  *ptr = 0;
+
+  /* output the significant digits */
+  while(value > 0) {
+    if(ptr == str)
+      return MTAR_EOVERFLOW;
+
+    --ptr;
+    *ptr = '0' + (value % 8);
+    value /= 8;
+  }
+
+  /* pad the remainder of the field with zeros */
+  while(ptr != str) {
+    --ptr;
+    *ptr = '0';
+  }
+
+  return MTAR_ESUCCESS;
+}
+
+
+static unsigned round_up(unsigned n, unsigned incr) {
+  return n + (incr - n % incr) % incr;
+}
+
+
+static unsigned checksum(const mtar_raw_header_t* rh) {
+  unsigned i;
+  unsigned char *p = (unsigned char*) rh;
+  unsigned res = 256;
+  for (i = 0; i < offsetof(mtar_raw_header_t, checksum); i++) {
+    res += p[i];
+  }
+  for (i = offsetof(mtar_raw_header_t, type); i < sizeof(*rh); i++) {
+    res += p[i];
+  }
+  return res;
+}
+
+
+static int tread(mtar_t *tar, void *data, unsigned size) {
+  int err = tar->read(tar, data, size);
+  tar->pos += size;
+  return err;
+}
+
+
+static int twrite(mtar_t *tar, const void *data, unsigned size) {
+  int err = tar->write(tar, data, size);
+  tar->pos += size;
+  return err;
+}
+
+
+static int write_null_bytes(mtar_t *tar, int n) {
+  int i, err;
+  char nul = '\0';
+  for (i = 0; i < n; i++) {
+    err = twrite(tar, &nul, 1);
+    if (err) {
+      return err;
+    }
+  }
+  return MTAR_ESUCCESS;
+}
+
+
+static int raw_to_header(mtar_header_t *h, const mtar_raw_header_t *rh) {
+  unsigned chksum1, chksum2;
+  int rc;
+
+  /* If the checksum starts with a null byte we assume the record is NULL */
+  if (*rh->checksum == '\0') {
+    return MTAR_ENULLRECORD;
+  }
+
+  /* Build and compare checksum */
+  chksum1 = checksum(rh);
+  if((rc = parse_octal(rh->checksum, sizeof(rh->checksum), &chksum2)))
+      return rc;
+  if (chksum1 != chksum2) {
+    return MTAR_EBADCHKSUM;
+  }
+
+  /* Load raw header into header */
+  if((rc = parse_octal(rh->mode, sizeof(rh->mode), &h->mode)))
+    return rc;
+  if((rc = parse_octal(rh->owner, sizeof(rh->owner), &h->owner)))
+    return rc;
+  if((rc = parse_octal(rh->group, sizeof(rh->group), &h->group)))
+    return rc;
+  if((rc = parse_octal(rh->size, sizeof(rh->size), &h->size)))
+    return rc;
+  if((rc = parse_octal(rh->mtime, sizeof(rh->mtime), &h->mtime)))
+    return rc;
+
+  h->type = rh->type;
+
+  memcpy(h->name, rh->name, sizeof(rh->name));
+  h->name[sizeof(h->name) - 1] = 0;
+
+  memcpy(h->linkname, rh->linkname, sizeof(rh->linkname));
+  h->linkname[sizeof(h->linkname) - 1] = 0;
+
+  return MTAR_ESUCCESS;
+}
+
+
+static int header_to_raw(mtar_raw_header_t *rh, const mtar_header_t *h) {
+  unsigned chksum;
+  int rc;
+
+  /* Load header into raw header */
+  memset(rh, 0, sizeof(*rh));
+  if((rc = print_octal(rh->mode, sizeof(rh->mode), h->mode)))
+    return rc;
+  if((rc = print_octal(rh->owner, sizeof(rh->owner), h->owner)))
+    return rc;
+  if((rc = print_octal(rh->group, sizeof(rh->group), h->group)))
+    return rc;
+  if((rc = print_octal(rh->size, sizeof(rh->size), h->size)))
+    return rc;
+  if((rc = print_octal(rh->mtime, sizeof(rh->mtime), h->mtime)))
+    return rc;
+  rh->type = h->type ? h->type : MTAR_TREG;
+  strncpy(rh->name, h->name, sizeof(rh->name));
+  strncpy(rh->linkname, h->linkname, sizeof(rh->linkname));
+
+  /* Calculate and write checksum */
+  chksum = checksum(rh);
+  if((rc = print_octal(rh->checksum, 7, chksum)))
+     return rc;
+  rh->checksum[7] = ' ';
+
+  return MTAR_ESUCCESS;
+}
+
+
+const char* mtar_strerror(int err) {
+  switch (err) {
+    case MTAR_ESUCCESS     : return "success";
+    case MTAR_EFAILURE     : return "failure";
+    case MTAR_EOPENFAIL    : return "could not open";
+    case MTAR_EREADFAIL    : return "could not read";
+    case MTAR_EWRITEFAIL   : return "could not write";
+    case MTAR_ESEEKFAIL    : return "could not seek";
+    case MTAR_EBADCHKSUM   : return "bad checksum";
+    case MTAR_ENULLRECORD  : return "null record";
+    case MTAR_ENOTFOUND    : return "file not found";
+    case MTAR_EOVERFLOW    : return "overflow";
+  }
+  return "unknown error";
+}
+
+
+int mtar_close(mtar_t *tar) {
+  return tar->close(tar);
+}
+
+
+int mtar_seek(mtar_t *tar, unsigned pos) {
+  int err = tar->seek(tar, pos);
+  tar->pos = pos;
+  return err;
+}
+
+
+int mtar_rewind(mtar_t *tar) {
+  tar->remaining_data = 0;
+  tar->last_header = 0;
+  return mtar_seek(tar, 0);
+}
+
+
+int mtar_next(mtar_t *tar) {
+  int err, n;
+  /* Load header */
+  err = mtar_read_header(tar, &tar->header);
+  if (err) {
+    return err;
+  }
+  /* Seek to next record */
+  n = round_up(tar->header.size, 512) + sizeof(mtar_raw_header_t);
+  return mtar_seek(tar, tar->pos + n);
+}
+
+
+int mtar_find(mtar_t *tar, const char *name, mtar_header_t *h) {
+  int err;
+  /* Start at beginning */
+  err = mtar_rewind(tar);
+  if (err) {
+    return err;
+  }
+  /* Iterate all files until we hit an error or find the file */
+  while ( (err = mtar_read_header(tar, &tar->header)) == MTAR_ESUCCESS ) {
+    if ( !strcmp(tar->header.name, name) ) {
+      if (h) {
+        *h = tar->header;
+      }
+      return MTAR_ESUCCESS;
+    }
+    err = mtar_next(tar);
+    if (err) {
+      return err;
+    }
+  }
+  /* Return error */
+  if (err == MTAR_ENULLRECORD) {
+    err = MTAR_ENOTFOUND;
+  }
+  return err;
+}
+
+
+int mtar_read_header(mtar_t *tar, mtar_header_t *h) {
+  int err;
+  /* Save header position */
+  tar->last_header = tar->pos;
+  /* Read raw header */
+  err = tread(tar, &tar->raw_header, sizeof(tar->raw_header));
+  if (err) {
+    return err;
+  }
+  /* Seek back to start of header */
+  err = mtar_seek(tar, tar->last_header);
+  if (err) {
+    return err;
+  }
+  /* Load raw header into header struct and return */
+  return raw_to_header(h, &tar->raw_header);
+}
+
+
+int mtar_read_data(mtar_t *tar, void *ptr, unsigned size) {
+  int err;
+  /* If we have no remaining data then this is the first read, we get the size,
+   * set the remaining data and seek to the beginning of the data */
+  if (tar->remaining_data == 0) {
+    /* Read header */
+    err = mtar_read_header(tar, &tar->header);
+    if (err) {
+      return err;
+    }
+    /* Seek past header and init remaining data */
+    err = mtar_seek(tar, tar->pos + sizeof(mtar_raw_header_t));
+    if (err) {
+      return err;
+    }
+    tar->remaining_data = tar->header.size;
+  }
+  /* Ensure caller does not read too much */
+  if(size > tar->remaining_data)
+    return MTAR_EOVERFLOW;
+  /* Read data */
+  err = tread(tar, ptr, size);
+  if (err) {
+    return err;
+  }
+  tar->remaining_data -= size;
+  /* If there is no remaining data we've finished reading and seek back to the
+   * header */
+  if (tar->remaining_data == 0) {
+    return mtar_seek(tar, tar->last_header);
+  }
+  return MTAR_ESUCCESS;
+}
+
+
+int mtar_write_header(mtar_t *tar, const mtar_header_t *h) {
+  /* Build raw header and write */
+  header_to_raw(&tar->raw_header, h);
+  tar->remaining_data = h->size;
+  return twrite(tar, &tar->raw_header, sizeof(tar->raw_header));
+}
+
+
+int mtar_write_file_header(mtar_t *tar, const char *name, unsigned size) {
+  /* Build header */
+  memset(&tar->header, 0, sizeof(tar->header));
+  /* Ensure name fits within header */
+  if(strlen(name) > sizeof(tar->header.name))
+    return MTAR_EOVERFLOW;
+  strncpy(tar->header.name, name, sizeof(tar->header.name));
+  tar->header.size = size;
+  tar->header.type = MTAR_TREG;
+  tar->header.mode = 0664;
+  /* Write header */
+  return mtar_write_header(tar, &tar->header);
+}
+
+
+int mtar_write_dir_header(mtar_t *tar, const char *name) {
+  /* Build header */
+  memset(&tar->header, 0, sizeof(tar->header));
+  /* Ensure name fits within header */
+  if(strlen(name) > sizeof(tar->header.name))
+    return MTAR_EOVERFLOW;
+  strncpy(tar->header.name, name, sizeof(tar->header.name));
+  tar->header.type = MTAR_TDIR;
+  tar->header.mode = 0775;
+  /* Write header */
+  return mtar_write_header(tar, &tar->header);
+}
+
+
+int mtar_write_data(mtar_t *tar, const void *data, unsigned size) {
+  int err;
+
+  /* Ensure we are writing the correct amount of data */
+  if(size > tar->remaining_data)
+    return MTAR_EOVERFLOW;
+
+  /* Write data */
+  err = twrite(tar, data, size);
+  if (err) {
+    return err;
+  }
+  tar->remaining_data -= size;
+  /* Write padding if we've written all the data for this file */
+  if (tar->remaining_data == 0) {
+    return write_null_bytes(tar, round_up(tar->pos, 512) - tar->pos);
+  }
+  return MTAR_ESUCCESS;
+}
+
+
+int mtar_finalize(mtar_t *tar) {
+  /* Write two NULL records */
+  return write_null_bytes(tar, sizeof(mtar_raw_header_t) * 2);
+}