4da3f6df0
Denys Vlasenko
2026-10-04
Subject
fatlabel: require dir_entries = 0 in FAT32 check; fix typos
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networking/tls_aes.c+1 -1
| @@ -170,7 +170,7 @@ static int KeyExpansion(uint32_t *RoundKey, const void *key, unsigned key_len) | |
| j = 0; | |
| k++; | |
| //TODO: we can eliminate k and Rcon[] and just generate Rcon[k]? | |
| - | //instead of k++, do: Rcon = (Rcon << 1) & ^ ((Rcon & 0x80) ? 0x1b : 0) |
| + | //instead of k++, do: Rcon = (Rcon << 1) ^ ((Rcon & 0x80) ? 0x1b : 0) |
| } | |
| } | |
| return rounds; | |
util-linux/fatlabel.c+34 -13
| @@ -8,7 +8,7 @@ | |
| //config: bool "fatlabel (1 kb)" | |
| //config: default y | |
| //config: help | |
| - | //config: fatlabel shows or sets FAT33 label. |
| + | //config: fatlabel shows or sets FAT32 label. |
| //applet:IF_FATLABEL(APPLET(fatlabel, BB_DIR_SBIN, BB_SUID_DROP)) | |
| @@ -75,17 +75,18 @@ struct msdos_dir_entry { | |
| */ | |
| struct msdos_volume_info { // (offsets are relative to start of boot sector) | |
| uint8_t drive_number; // 040 BIOS drive number | |
| - | uint8_t reserved; // 041 unused |
| - | uint8_t ext_boot_sign; // 042 0x29 if fields below exist (DOS 3.3+) |
| + | uint8_t reserved; // 041 'unused'. Linux uses this for 0x01 'mounted now' bit, some WinNT too? |
| + | uint8_t ext_boot_sign; // 042 0x28 (40) if volume_id32 exists, 0x29 (41) if all three fields below exist (0x29 is 'standard' since DOS 4.0). |
| uint32_t volume_id32; // 043 volume ID number | |
| char volume_label[11];// 047 volume label | |
| - | char fs_type[8]; // 052 typically "FATnn" |
| + | char fs_type[8]; // 052 typically "FATnn " |
| } PACKED; // 05a end. Total size 26 (0x1a) bytes | |
| struct msdos_boot_sector { | |
| // We use strcpy to fill both, and gcc-4.4.x complains if they are separate | |
| char boot_jump_and_sys_id[3+8]; //000 short or near jump instruction | |
| - | /*char system_id[8];*/ // 003 name - can be used to special case partition manager volumes |
| + | /*char system_id[8];*/ // 003 usually formatting util's id: "MSDOSn.n", "MSWINn.n", "mkfs.fat", "mkdosfs\0" (ours). |
| + | // "EXFAT " and "NTFS " are required signatures for those filesystems at this offset |
| uint16_t bytes_per_sect; // 00b bytes per logical sector | |
| uint8_t sect_per_clust; // 00d sectors/cluster | |
| uint16_t reserved_sect; // 00e reserved sectors (sector offset of 1st FAT relative to volume start) | |
| @@ -104,13 +105,33 @@ struct msdos_boot_sector { | |
| uint32_t fat32_root_cluster; // 02c first cluster in root directory | |
| uint16_t fat32_info_sector; // 030 filesystem info sector (usually 1) | |
| uint16_t fat32_backup_boot; // 032 backup boot sector (usually 6) | |
| - | uint32_t reserved2[3]; // 034 unused |
| + | uint32_t reserved2[3]; // 034 'unused'. 12 bytes of 'boot file name'? |
| struct msdos_volume_info vi; // 040 | |
| char boot_code[0x200 - 0x5a - 2]; // 05a | |
| #define BOOT_SIGN 0xAA55 | |
| uint16_t boot_sign; // 1fe | |
| } PACKED; | |
| + | // Microsoft's EFI FAT32 specification states that any FAT file system with |
| + | // less than 4085 clusters is FAT12, else any FAT file system with less than |
| + | // 65525 clusters is FAT16, and otherwise it is FAT32. The entry for cluster |
| + | // 0 at the beginning of the FAT must be identical to the media descriptor byte |
| + | // found in the BPB, whereas the entry for cluster 1 reflects the end-of-chain |
| + | // value used by the formatter for cluster chains (0xFFF, 0xFFFF or 0x0FFFFFFF). |
| + | // The entries for cluster numbers 0 and 1 end at a byte boundary even |
| + | // for FAT12, e.g., 0xF9FFFF for media descriptor 0xF9. |
| + | // |
| + | // In practice, FAT12/16 has to have nonzero fat16_sect_per_fat field. |
| + | // (it never needs more than 16 bits for this value, unlike FAT32). |
| + | // If it is zero, it is either not a FAT fs at all, or it is FAT32. |
| + | // Unknown whether converse is true (can small FAT32 fs exist with |
| + | // fat16_sect_per_fat field set to nonzero?). |
| + | // |
| + | // A better field for FAT32 discrimination is dir_entries. |
| + | // By necessity, it has to be nonzero for FAT12/16 (you have to have |
| + | // a non-empty root dir). It does not make sense for FAT32 whose root dir |
| + | // is not fixed size, thus presumably always 0. |
| + | |
| #define FAT_FSINFO_SIG1 0x41615252 | |
| #define FAT_FSINFO_SIG2 0x61417272 | |
| struct fat32_fsinfo { | |
| @@ -151,7 +172,7 @@ static int bad_fat32(const struct msdos_boot_sector *boot_blk) | |
| move_from_unaligned16(bytes_per_sect16, &boot_blk->bytes_per_sect); | |
| return ((uint8_t)(boot_blk->fats - 1) > 1 // 0 or >2 | |
| || boot_blk->fat16_sect_per_fat != 0 | |
| - | // maybe also check boot_blk->dir_entries == 0? It's only for FAT16/12 |
| + | || boot_blk->dir_entries != 0 |
| || boot_blk->vi.ext_boot_sign != 0x29 | |
| || boot_blk->boot_sign != SWAP_LE16(BOOT_SIGN) | |
| || bytes_per_sect16 != SWAP_LE16(SECTOR_SIZE) | |
| @@ -179,12 +200,12 @@ int fatlabel_main(int argc UNUSED_PARAM, char **argv) | |
| #if 0 | |
| fprintf(stderr, | |
| "0x003: sys_id:'%.8s'\n" | |
| - | "0x00b: bytes_per_sect: 0x%04x\n" // 0 |
| - | "0x00d: sect_per_clust: 0x%02x\n" // 0 |
| + | "0x00b: bytes_per_sect: 0x%04x\n" // 0x200 |
| + | "0x00d: sect_per_clust: 0x%02x\n" |
| "0x010: fats: 0x%02x\n" // 1 or 2 | |
| - | "0x011: dir_entries: 0x%04x\n" // always 0 for FAT32? |
| + | "0x011: dir_entries: 0x%04x\n" // always !0 for FAT12/16! Always 0 for FAT32? |
| "0x015: media_byte: 0x%02x\n" // 0xf8 for "hard disk" | |
| - | "0x016: fat16_sect_per_fat: 0x%04x\n" // 0 |
| + | "0x016: fat16_sect_per_fat: 0x%04x\n" // Always 0 for FAT32? |
| "0x028: fat32_flags: 0x%04x\n" // 0,0 | |
| "0x02a: fat32_version: 0x%02x,0x%02x\n" // 0,0 | |
| "0x030: fat32_info_sector: 0x%04x\n" // always 1? | |
| @@ -206,7 +227,7 @@ int fatlabel_main(int argc UNUSED_PARAM, char **argv) | |
| , boot_blk->fat32_version[0], boot_blk->fat32_version[1] | |
| , FETCH_LE16(boot_blk->fat32_info_sector) | |
| , backup_boot_sect | |
| - | , boot_blk->vi.reserved // Linux uses this as "mounted now" bit, some WinNT too? |
| + | , boot_blk->vi.reserved // Linux uses this for 0x01 "mounted now" bit, some WinNT too? |
| , boot_blk->vi.ext_boot_sign | |
| , FETCH_LE32(boot_blk->vi.volume_id32) // FIXME: unaligned fetch | |
| , boot_blk->vi.volume_label | |
| @@ -238,7 +259,7 @@ int fatlabel_main(int argc UNUSED_PARAM, char **argv) | |
| sprintf(boot_blk->vi.volume_label, "%-11.11s", argv[1]); | |
| xlseek(fd, 0x047, SEEK_SET); | |
| xwrite(fd, boot_blk->vi.volume_label, 11); | |
| - | // Redundant is backup_boot_sect == 0, but no harm done: |
| + | // Redundant if backup_boot_sect == 0, but no harm done: |
| xlseek(fd, 0x047 + backup_boot_sect * SECTOR_SIZE, SEEK_SET); | |
| xwrite(fd, boot_blk->vi.volume_label, 11); | |
| } else { | |