#include <stdio.h> #include <stdlib.h> #include <string.h> #include <assert.h> #include <openssl/sha.h> #include "fat32.h" #include "utils.h" void printFsInfo(BootEntry *bootEntry) { printf("Number of FATs = %d\n" "Number of bytes per sector = %d\n" "Number of sectors per cluster = %d\n" "Number of reserved sectors = %d\n", bootEntry -> BPB_NumFATs, bootEntry -> BPB_BytsPerSec, bootEntry -> BPB_SecPerClus, bootEntry -> BPB_RsvdSecCnt); } char *formattedDirName(DirEntry *dirEntry) { char *formattedName = malloc(sizeof(char) * 13); int j = 0; /* Grab the main part of the file name */ for (int i = 0; i < 8; i ++) { if (dirEntry -> DIR_Name[i] == 0x20) break; formattedName[j ++] = dirEntry -> DIR_Name[i]; } /* The directory entry is a file container (i.e., another directory) */ if (dirEntry -> DIR_Attr == 0x10) { formattedName[j ++] = '/'; } /* The directory entry has a file extension */ else if (dirEntry -> DIR_Name[8] != 0x20) { formattedName[j ++] = '.'; for (int i = 8; i < 11; i ++) { if (dirEntry -> DIR_Name[i] == 0x20) break; formattedName[j ++] = dirEntry -> DIR_Name[i]; } } return formattedName; } int printDirInfo(DirEntry *dirEntry) { /* The directory entry has a long file name or is freed */ if (dirEntry -> DIR_Attr == (0x01 | 0x02 | 0x04 | 0x08)) return -1; if (dirEntry -> DIR_Name[0] == 0xE5 || dirEntry -> DIR_Name[0] == 0x05) return -1; char *formattedName = formattedDirName(dirEntry); printf("%s (size = %d, starting cluster = %d)\n", formattedName, dirEntry -> DIR_FileSize, (dirEntry -> DIR_FstClusHI << 16) | dirEntry -> DIR_FstClusLO); free(formattedName); return 0; } int delContEntryIndex(char *fileName, char *sCode, char *disk, BootEntry *bootEntry, DirEntry **rootDirEntries, int dirEntryCount) { int target = -1; char *formattedName; for (int i = 0; i < dirEntryCount; i ++) { /* The entry is marked as freed */ if (rootDirEntries[i] -> DIR_Name[0] == 0xE5) { formattedName = formattedDirName(rootDirEntries[i]); if (strcmp(formattedName + 1, fileName + 1) == 0) { free(formattedName); if (sCode == NULL) { /* Multiple freed entires with the same name */ if (target >= 0) return -2; target = i; } else { unsigned int curCluster = (rootDirEntries[i] -> DIR_FstClusHI << 16) | rootDirEntries[i] -> DIR_FstClusLO; /* The target file is not empty */ if (curCluster != 0) { SHA_CTX ctx; SHA1_Init(&ctx); unsigned int j = 0; unsigned int BPB_BytsPerClus = bootEntry -> BPB_BytsPerSec * bootEntry -> BPB_SecPerClus; /* SHA1 hash file contents for the next contiguous cluster */ while (rootDirEntries[i] -> DIR_FileSize > BPB_BytsPerClus * (j + 1)) { SHA1_Update(&ctx, disk + followFAT(bootEntry, &curCluster, disk, 0), BPB_BytsPerClus); j ++; curCluster ++; } /* SHA1 hash file contents for the last cluster */ SHA1_Update(&ctx, disk + followFAT(bootEntry, &curCluster, disk, 0), rootDirEntries[i] -> DIR_FileSize - BPB_BytsPerClus * j); unsigned char fSha1[SHA_DIGEST_LENGTH]; SHA1_Final(fSha1, &ctx); /* File content hash matches the specified SHA1 code */ if (hashMatch(fSha1, sCode)) return i; } /* The target file is empty */ else if (strcmp(sCode, SHA1EMPTY) == 0) return i; } } } } return target; } int delNonContClusters(char *fileName, char *sCode, char *disk, BootEntry *bootEntry, DirEntry **rootDirEntries, int dirEntryCount, unsigned int *targetClusters) { /* The array in which the positions for the first cluster of some root directory entry are marked 1 */ unsigned int occupied[22]; for (int i = 0; i < 22; i ++) occupied[i] = 0; for (int i = 0; i < dirEntryCount; i ++) { occupied[(rootDirEntries[i] -> DIR_FstClusHI << 16) | rootDirEntries[i] -> DIR_FstClusLO] = 1; } /* The array of clusters that are not the first cluster of any root directory entry, within the range [2, 22) */ int nonFirstClusterCount = 0; unsigned int nonFirstClusters[20]; for (unsigned int i = 2; i < 22; i ++) { if (!occupied[i]) nonFirstClusters[nonFirstClusterCount ++] = i; } int target = -1; char *formattedName; for (int i = 0; i < dirEntryCount; i ++) { /* The entry is marked as freed */ if (rootDirEntries[i] -> DIR_Name[0] == 0xE5) { formattedName = formattedDirName(rootDirEntries[i]); if (strcmp(formattedName + 1, fileName + 1) == 0) { free(formattedName); unsigned int firstCluster = (rootDirEntries[i] -> DIR_FstClusHI << 16) | rootDirEntries[i] -> DIR_FstClusLO; /* The target file is not empty */ if (firstCluster != 0) { unsigned int BPB_BytsPerClus = bootEntry -> BPB_BytsPerSec * bootEntry -> BPB_SecPerClus; unsigned int targetClusterCount = rootDirEntries[i] -> DIR_FileSize / BPB_BytsPerClus + 1; /* Except for the first cluster, traverse all possible permutations of other clusters */ unsigned int totalPermutations = 1; for (unsigned int j = 0; j < targetClusterCount - 1; j ++) totalPermutations *= nonFirstClusterCount - j; unsigned int **permutations = permute(nonFirstClusters, nonFirstClusterCount, targetClusterCount - 1); for (unsigned int j = 0; j < totalPermutations; j ++) { SHA_CTX ctx; SHA1_Init(&ctx); if (targetClusterCount == 1) { SHA1_Update(&ctx, disk + followFAT(bootEntry, &firstCluster, disk, 0), rootDirEntries[i] -> DIR_FileSize); } else { /* SHA1 hash contents for this permutation of clusters */ SHA1_Update(&ctx, disk + followFAT(bootEntry, &firstCluster, disk, 0), BPB_BytsPerClus); for (unsigned int k = 0; k < targetClusterCount - 2; k ++) { SHA1_Update(&ctx, disk + followFAT(bootEntry, &permutations[j][k], disk, 0), BPB_BytsPerClus); } /* SHA1 hash file contents for the last cluster */ SHA1_Update(&ctx, disk + followFAT(bootEntry, &permutations[j][targetClusterCount - 2], disk, 0), rootDirEntries[i] -> DIR_FileSize - BPB_BytsPerClus * (targetClusterCount - 1)); } unsigned char fSha1[SHA_DIGEST_LENGTH]; SHA1_Final(fSha1, &ctx); if (hashMatch(fSha1, sCode)) { targetClusters[0] = targetClusterCount; targetClusters[1] = firstCluster; for (unsigned int k = 0; k < targetClusterCount - 1; k ++) { targetClusters[k + 2] = permutations[j][k]; } /* Free the permutation array and its pointers */ for (unsigned int k = 0; k < totalPermutations; k ++) free(permutations[k]); free(permutations); return i; } } /* Free the permutation array and its pointers */ for (unsigned int j = 0; j < totalPermutations; j ++) free(permutations[j]); free(permutations); } /* The target file is empty */ else if (strcmp(sCode, SHA1EMPTY) == 0) { targetClusters[0] = 0; return i; } } } } return target; } unsigned long followFAT(BootEntry *bootEntry, unsigned int *cluster, char *disk, int mode) { /* In FAT32, the cluster number starts with 2 */ int curCluster = *cluster; assert(curCluster >= 2); /* FAT area, each taking 4 bytes, starting with cluster 0 */ if (mode) memcpy(cluster, disk + bootEntry -> BPB_RsvdSecCnt * bootEntry -> BPB_BytsPerSec + curCluster * 4, 4); /* Data area, each taking 32 bytes, starting with cluster 2 */ return (bootEntry -> BPB_RsvdSecCnt + bootEntry -> BPB_NumFATs * bootEntry -> BPB_FATSz32) * bootEntry -> BPB_BytsPerSec + (curCluster - 2) * bootEntry -> BPB_BytsPerSec * bootEntry -> BPB_SecPerClus; } void updateFATs(BootEntry *bootEntry, unsigned int cluster, char *disk, unsigned int DIR_NextClus) { unsigned long offset; /* Update all FATs */ for (int i = 0; i < bootEntry -> BPB_NumFATs; i ++) { /* FAT area, each taking 4 bytes, starting with cluster 0 */ offset = (bootEntry -> BPB_RsvdSecCnt + i * bootEntry -> BPB_FATSz32) * bootEntry -> BPB_BytsPerSec + cluster * 4; memcpy(disk + offset, &DIR_NextClus, 4); } }