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improve reliability of fixup_pack_header_footer()

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Currently, this function has the potential to read corrupted pack data
from disk and give it a valid SHA1 checksum.  Let's add the ability to
validate SHA1 checksum of existing data along the way, including before
and after any arbitrary point in the pack.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Nicolas Pitre
2008-08-29 16:07:59 -04:00
committed by Junio C Hamano
parent 6ed7f25e95
commit abeb40e5aa
5 changed files with 66 additions and 16 deletions
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71
pack-write.c
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@ -144,41 +144,88 @@ char *write_idx_file(char *index_name, struct pack_idx_entry **objects,
return index_name;
}
/*
* Update pack header with object_count and compute new SHA1 for pack data
* associated to pack_fd, and write that SHA1 at the end. That new SHA1
* is also returned in new_pack_sha1.
*
* If partial_pack_sha1 is non null, then the SHA1 of the existing pack
* (without the header update) is computed and validated against the
* one provided in partial_pack_sha1. The validation is performed at
* partial_pack_offset bytes in the pack file. The SHA1 of the remaining
* data (i.e. from partial_pack_offset to the end) is then computed and
* returned in partial_pack_sha1.
*
* Note that new_pack_sha1 is updated last, so both new_pack_sha1 and
* partial_pack_sha1 can refer to the same buffer if the caller is not
* interested in the resulting SHA1 of pack data above partial_pack_offset.
*/
void fixup_pack_header_footer(int pack_fd,
unsigned char *pack_file_sha1,
unsigned char *new_pack_sha1,
const char *pack_name,
uint32_t object_count)
uint32_t object_count,
unsigned char *partial_pack_sha1,
off_t partial_pack_offset)
{
static const int buf_sz = 128 * 1024;
SHA_CTX c;
SHA_CTX old_sha1_ctx, new_sha1_ctx;
struct pack_header hdr;
char *buf;
SHA1_Init(&old_sha1_ctx);
SHA1_Init(&new_sha1_ctx);
if (lseek(pack_fd, 0, SEEK_SET) != 0)
die("Failed seeking to start: %s", strerror(errno));
die("Failed seeking to start of %s: %s", pack_name, strerror(errno));
if (read_in_full(pack_fd, &hdr, sizeof(hdr)) != sizeof(hdr))
die("Unable to reread header of %s: %s", pack_name, strerror(errno));
if (lseek(pack_fd, 0, SEEK_SET) != 0)
die("Failed seeking to start: %s", strerror(errno));
die("Failed seeking to start of %s: %s", pack_name, strerror(errno));
SHA1_Update(&old_sha1_ctx, &hdr, sizeof(hdr));
hdr.hdr_entries = htonl(object_count);
SHA1_Update(&new_sha1_ctx, &hdr, sizeof(hdr));
write_or_die(pack_fd, &hdr, sizeof(hdr));
SHA1_Init(&c);
SHA1_Update(&c, &hdr, sizeof(hdr));
partial_pack_offset -= sizeof(hdr);
buf = xmalloc(buf_sz);
for (;;) {
ssize_t n = xread(pack_fd, buf, buf_sz);
ssize_t m, n;
m = (partial_pack_sha1 && partial_pack_offset < buf_sz) ?
partial_pack_offset : buf_sz;
n = xread(pack_fd, buf, m);
if (!n)
break;
if (n < 0)
die("Failed to checksum %s: %s", pack_name, strerror(errno));
SHA1_Update(&c, buf, n);
SHA1_Update(&new_sha1_ctx, buf, n);
if (!partial_pack_sha1)
continue;
SHA1_Update(&old_sha1_ctx, buf, n);
partial_pack_offset -= n;
if (partial_pack_offset == 0) {
unsigned char sha1[20];
SHA1_Final(sha1, &old_sha1_ctx);
if (hashcmp(sha1, partial_pack_sha1) != 0)
die("Unexpected checksum for %s "
"(disk corruption?)", pack_name);
/*
* Now let's compute the SHA1 of the remainder of the
* pack, which also means making partial_pack_offset
* big enough not to matter anymore.
*/
SHA1_Init(&old_sha1_ctx);
partial_pack_offset = ~partial_pack_offset;
partial_pack_offset -= MSB(partial_pack_offset, 1);
}
}
free(buf);
SHA1_Final(pack_file_sha1, &c);
write_or_die(pack_fd, pack_file_sha1, 20);
if (partial_pack_sha1)
SHA1_Final(partial_pack_sha1, &old_sha1_ctx);
SHA1_Final(new_pack_sha1, &new_sha1_ctx);
write_or_die(pack_fd, new_pack_sha1, 20);
fsync_or_die(pack_fd, pack_name);
}