diff options
Diffstat (limited to 'tar/read_header.c')
| -rw-r--r-- | tar/read_header.c | 379 |
1 files changed, 379 insertions, 0 deletions
diff --git a/tar/read_header.c b/tar/read_header.c new file mode 100644 index 0000000..099a9ce --- /dev/null +++ b/tar/read_header.c @@ -0,0 +1,379 @@ +/* SPDX-License-Identifier: GPL-3.0-or-later */ +#include "util.h" +#include "tar.h" + +#include <string.h> +#include <stdlib.h> +#include <ctype.h> +#include <stdio.h> + +enum { + PAX_SIZE = 0x01, + PAX_UID = 0x02, + PAX_GID = 0x04, + PAX_DEV_MAJ = 0x08, + PAX_DEV_MIN = 0x10, + PAX_NAME = 0x20, + PAX_SLINK_TARGET = 0x40, +}; + +static int read_octal(const char *str, int digits, uint64_t *out) +{ + uint64_t result = 0; + + while (digits > 0 && *str >= '0' && *str <= '7') { + if (result > 0x1FFFFFFFFFFFFFFFUL) { + fputs("numeric overflow parsing tar header\n", stderr); + return -1; + } + + result = (result << 3) | (*(str++) - '0'); + --digits; + } + + *out = result; + return 0; +} + +static int read_binary(const char *str, int digits, uint64_t *out) +{ + uint64_t x, result = 0; + + while (digits > 0) { + if (result > 0x00FFFFFFFFFFFFFFUL) { + fputs("numeric overflow parsing tar header\n", stderr); + return -1; + } + + x = *((const unsigned char *)str++); + result = (result << 8) | x; + --digits; + } + + *out = result; + return 0; +} + +static int read_number(const char *str, int digits, uint64_t *out) +{ + if (*((unsigned char *)str) & 0x80) { + if (read_binary(str, digits, out)) + return -1; + *out &= 0x7FFFFFFFFFFFFFFF; + return 0; + } + + return read_octal(str, digits, out); +} + +static bool is_zero_block(const tar_header_t *hdr) +{ + const unsigned char *ptr = (const unsigned char *)hdr; + + return ptr[0] == '\0' && memcmp(ptr, ptr + 1, sizeof(*hdr) - 1) == 0; +} + +static bool is_checksum_valid(const tar_header_t *hdr) +{ + unsigned int chksum = 0; + tar_header_t copy; + uint64_t ref; + size_t i; + + if (read_octal(hdr->chksum, sizeof(hdr->chksum), &ref)) + return false; + + memcpy(©, hdr, sizeof(*hdr)); + memset(copy.chksum, ' ', sizeof(copy.chksum)); + + for (i = 0; i < sizeof(copy); ++i) + chksum += ((unsigned char *)©)[i]; + + return chksum == ref; +} + +static bool is_magic_valid(const tar_header_t *hdr) +{ + if (memcmp(hdr->magic, TAR_MAGIC, sizeof(hdr->magic)) != 0) + return false; + + if (memcmp(hdr->version, TAR_VERSION, sizeof(hdr->version)) != 0) + return false; + + return true; +} + +static int pax_read_decimal(const char *str, uint64_t *out) +{ + uint64_t result = 0; + + while (*str >= '0' && *str <= '9') { + if (result > 0xFFFFFFFFFFFFFFFFUL / 10) { + fputs("numeric overflow parsing pax header\n", stderr); + return -1; + } + + result = (result * 10) + (*(str++) - '0'); + } + + *out = result; + return 0; +} + +static int read_pax_header(int fd, uint64_t entsize, unsigned int *set_by_pax, + tar_header_decoded_t *out) +{ + char *buffer, *line; + ssize_t ret; + uint64_t i; + + buffer = malloc(entsize + 1); + if (buffer == NULL) + goto fail_errno; + + ret = read_retry(fd, buffer, entsize); + if (ret < 0) + goto fail_errno; + if ((size_t)ret < entsize) + goto fail_eof; + + if (skip_padding(fd, entsize)) + goto fail; + + buffer[entsize] = '\0'; + + for (i = 0; i < entsize; ++i) { + while (i < entsize && isspace(buffer[i])) + ++i; + while (i < entsize && isdigit(buffer[i])) + ++i; + while (i < entsize && isspace(buffer[i])) + ++i; + if (i >= entsize) + break; + + line = buffer + i; + + while (i < entsize && buffer[i] != '\n') + ++i; + + buffer[i] = '\0'; + + if (!strncmp(line, "uid=", 4)) { + pax_read_decimal(line + 4, &out->uid); + *set_by_pax |= PAX_UID; + } else if (!strncmp(line, "gid=", 4)) { + pax_read_decimal(line + 4, &out->gid); + *set_by_pax |= PAX_GID; + } else if (!strncmp(line, "path=", 5)) { + free(out->name); + out->name = strdup(line + 5); + if (out->name == NULL) + goto fail_errno; + *set_by_pax |= PAX_NAME; + } else if (!strncmp(line, "size=", 5)) { + pax_read_decimal(line + 5, &out->size); + *set_by_pax |= PAX_SIZE; + } else if (!strncmp(line, "linkpath=", 9)) { + free(out->link_target); + out->link_target = strdup(line + 9); + if (out->link_target == NULL) + goto fail_errno; + *set_by_pax |= PAX_SLINK_TARGET; + } + } + + free(buffer); + return 0; +fail_errno: + perror("reading pax header"); + goto fail; +fail_eof: + fputs("reading pax header: unexpected end of file\n", stderr); + goto fail; +fail: + free(buffer); + return -1; +} + +static int decode_header(const tar_header_t *hdr, unsigned int set_by_pax, + tar_header_decoded_t *out) +{ + size_t count; + + if (!(set_by_pax & PAX_NAME)) { + if (hdr->prefix[0] == '\0') { + count = strlen(hdr->name) + 1; + count += strlen(hdr->prefix) + 1; + + out->name = malloc(count); + + if (out->name != NULL) { + sprintf(out->name, "%s/%s", + hdr->prefix, hdr->name); + } + } else { + out->name = strdup(hdr->name); + } + + if (out->name == NULL) { + perror("decoding filename"); + return -1; + } + } + + if (!(set_by_pax & PAX_SIZE)) { + if (read_number(hdr->size, sizeof(hdr->size), &out->size)) + return -1; + } + + if (!(set_by_pax & PAX_UID)) { + if (read_number(hdr->uid, sizeof(hdr->uid), &out->uid)) + return -1; + } + + if (!(set_by_pax & PAX_GID)) { + if (read_number(hdr->gid, sizeof(hdr->gid), &out->gid)) + return -1; + } + + if (!(set_by_pax & PAX_DEV_MAJ)) { + if (read_number(hdr->devmajor, sizeof(hdr->devmajor), + &out->dev_maj)) { + return -1; + } + } + + if (!(set_by_pax & PAX_DEV_MIN)) { + if (read_number(hdr->devminor, sizeof(hdr->devminor), + &out->dev_min)) { + return -1; + } + } + + if (read_octal(hdr->mode, sizeof(hdr->mode), &out->mode)) + return -1; + + out->mode &= 07777; + + if (hdr->typeflag == TAR_TYPE_LINK || + hdr->typeflag == TAR_TYPE_SLINK) { + if (!(set_by_pax & PAX_SLINK_TARGET)) { + out->link_target = strdup(hdr->linkname); + if (out->link_target == NULL) { + perror("decoding symlink target"); + return -1; + } + } + } + + out->unknown_record = false; + + switch (hdr->typeflag) { + case '\0': + case TAR_TYPE_FILE: + out->mode |= S_IFREG; + break; + case TAR_TYPE_LINK: + /* XXX: hard links are not support yet */ + out->mode = S_IFLNK | 0777; + break; + case TAR_TYPE_SLINK: + out->mode = S_IFLNK | 0777; + break; + case TAR_TYPE_CHARDEV: + out->mode |= S_IFCHR; + break; + case TAR_TYPE_BLOCKDEV: + out->mode |= S_IFBLK; + break; + case TAR_TYPE_DIR: + out->mode |= S_IFDIR; + break; + case TAR_TYPE_FIFO: + out->mode |= S_IFIFO; + break; + default: + out->unknown_record = true; + break; + } + + return 0; +} + +int read_header(int fd, tar_header_decoded_t *out) +{ + unsigned int set_by_pax = 0; + bool prev_was_zero = false; + uint64_t pax_size; + tar_header_t hdr; + int ret; + + memset(out, 0, sizeof(*out)); + + for (;;) { + ret = read_retry(fd, &hdr, sizeof(hdr)); + if (ret == 0) + goto out_eof; + if (ret < 0) + goto fail_errno; + if (ret < (int)sizeof(hdr)) + goto fail_eof; + + if (is_zero_block(&hdr)) { + if (prev_was_zero) + goto out_eof; + prev_was_zero = true; + continue; + } + + prev_was_zero = false; + + if (!is_magic_valid(&hdr)) + goto fail_magic; + + if (!is_checksum_valid(&hdr)) + goto fail_chksum; + + if (hdr.typeflag == TAR_TYPE_PAX) { + clear_header(out); + if (read_number(hdr.size, sizeof(hdr.size), &pax_size)) + return -1; + set_by_pax = 0; + if (read_pax_header(fd, pax_size, &set_by_pax, out)) + return -1; + continue; + } + break; + } + + if (decode_header(&hdr, set_by_pax, out)) + goto fail; + + return 0; +out_eof: + clear_header(out); + return 1; +fail_errno: + perror("reading tar header"); + goto fail; +fail_eof: + fputs("reading tar header: unexpected end of file\n", stderr); + goto fail; +fail_magic: + fputs("input is not a ustar tar archive!\n", stderr); + goto fail; +fail_chksum: + fputs("invalid tar header checksum!\n", stderr); + goto fail; +fail: + clear_header(out); + return -1; +} + +void clear_header(tar_header_decoded_t *hdr) +{ + free(hdr->name); + free(hdr->link_target); + memset(hdr, 0, sizeof(*hdr)); +} |