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feat: calculate header checksums and validate them against hdr->chksum

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Fixes #2.
This commit is contained in:
apio 2023-01-11 21:02:37 +01:00
parent f2f4d4ddab
commit 7b83dce96a
Signed by: apio
GPG Key ID: B8A7D06E42258954
1 changed files with 28 additions and 0 deletions
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28
src/util.c
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@ -196,6 +196,32 @@ void minitar_parse_metadata_from_tar_header(const struct tar_header* hdr, struct
minitar_strlcpy(metadata->gname, hdr->gname, 32);
}
uint32_t minitar_checksum_header(const struct tar_header* hdr)
{
uint32_t sum = 0;
const uint8_t* ptr = (const uint8_t*)hdr;
// Sum up all bytes in the header, as unsigned bytes...
while (ptr < (const uint8_t*)hdr + sizeof *hdr)
{
sum += *ptr;
ptr++;
}
// except for the chksum field, which is treated as...
ptr = (const uint8_t*)hdr->chksum;
while (ptr < (const uint8_t*)hdr->chksum + sizeof hdr->chksum)
{
sum -= *ptr;
ptr++;
}
// all blanks.
for (size_t i = 0; i < sizeof hdr->chksum; i++) { sum += ' '; }
return sum;
}
int minitar_validate_header(const struct tar_header* hdr)
{
#ifdef MINITAR_IGNORE_UNSUPPORTED_TYPES
@ -205,6 +231,8 @@ int minitar_validate_header(const struct tar_header* hdr)
hdr->typeflag != '3' && hdr->typeflag != '4' && hdr->typeflag != '5' && hdr->typeflag != '6')
return 0;
#endif
// FIXME: Warn on checksum mismatch unless header is all blanks?
if (minitar_checksum_header(hdr) != minitar_parse_octal(hdr->chksum)) return 0;
return !strncmp(hdr->magic, "ustar", 5);
}