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-rw-r--r--lib/tar/checksum.c31
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(&copy, hdr, sizeof(*hdr));
- update_checksum(&copy);
- return memcmp(hdr, &copy, sizeof(*hdr)) == 0;
+ if (read_octal(hdr->chksum, sizeof(hdr->chksum), &read_chksum))
+ return 0;
+ return read_chksum == calculated_chksum;
}