diff options
Diffstat (limited to 'lib/tar/checksum.c')
| -rw-r--r-- | lib/tar/checksum.c | 31 |
1 files changed, 22 insertions, 9 deletions
diff --git a/lib/tar/checksum.c b/lib/tar/checksum.c index a2a101a..af94ab4 100644 --- a/lib/tar/checksum.c +++ b/lib/tar/checksum.c @@ -1,15 +1,27 @@ /* SPDX-License-Identifier: GPL-3.0-or-later */ #include "internal.h" -void update_checksum(tar_header_t *hdr) +static unsigned int get_checksum(const tar_header_t *hdr) { + const unsigned char *header_start = (const unsigned char *)hdr; + const unsigned char *chksum_start = (const unsigned char *)hdr->chksum; + const unsigned char *header_end = header_start + sizeof(*hdr); + const unsigned char *chksum_end = chksum_start + sizeof(hdr->chksum); + const unsigned char *p; unsigned int chksum = 0; - size_t i; - memset(hdr->chksum, ' ', sizeof(hdr->chksum)); + for (p = header_start; p < chksum_start; p++) + chksum += *p; + for (; p < chksum_end; p++) + chksum += ' '; + for (; p < header_end; p++) + chksum += *p; + return chksum; +} - for (i = 0; i < sizeof(*hdr); ++i) - chksum += ((unsigned char *)hdr)[i]; +void update_checksum(tar_header_t *hdr) +{ + unsigned int chksum = get_checksum(hdr); sprintf(hdr->chksum, "%06o", chksum); hdr->chksum[6] = '\0'; @@ -18,9 +30,10 @@ void update_checksum(tar_header_t *hdr) bool is_checksum_valid(const tar_header_t *hdr) { - tar_header_t copy; + unsigned int calculated_chksum = get_checksum(hdr); + uint64_t read_chksum; - memcpy(©, hdr, sizeof(*hdr)); - update_checksum(©); - return memcmp(hdr, ©, sizeof(*hdr)) == 0; + if (read_octal(hdr->chksum, sizeof(hdr->chksum), &read_chksum)) + return 0; + return read_chksum == calculated_chksum; } |