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improve reliability of fixup_pack_header_footer()

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>
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1 parent 6ed7f25 commit abeb40e5aa5b4a39799ae1caad241c8c7708053a Nicolas Pitre committed with gitster
Showing with 66 additions and 16 deletions.
  1. +2 −1 builtin-pack-objects.c
  2. +2 −1 fast-import.c
  3. +2 −1 index-pack.c
  4. +59 −12 pack-write.c
  5. +1 −1 pack.h
View
3 builtin-pack-objects.c
@@ -493,7 +493,8 @@ static void write_pack_file(void)
sha1close(f, sha1, CSUM_FSYNC);
} else {
int fd = sha1close(f, NULL, 0);
- fixup_pack_header_footer(fd, sha1, pack_tmp_name, nr_written);
+ fixup_pack_header_footer(fd, sha1, pack_tmp_name,
+ nr_written, NULL, 0);
close(fd);
}
View
3 fast-import.c
@@ -951,7 +951,8 @@ static void end_packfile(void)
close_pack_windows(pack_data);
fixup_pack_header_footer(pack_data->pack_fd, pack_data->sha1,
- pack_data->pack_name, object_count);
+ pack_data->pack_name, object_count,
+ NULL, 0);
close(pack_data->pack_fd);
idx_name = keep_pack(create_index());
View
3 index-pack.c
@@ -982,7 +982,8 @@ int main(int argc, char **argv)
nr_objects - nr_objects_initial);
stop_progress_msg(&progress, msg);
fixup_pack_header_footer(output_fd, sha1,
- curr_pack, nr_objects);
+ curr_pack, nr_objects,
+ NULL, 0);
}
if (nr_deltas != nr_resolved_deltas)
die("pack has %d unresolved deltas",
View
71 pack-write.c
@@ -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);
}
View
2 pack.h
@@ -58,7 +58,7 @@ struct pack_idx_entry {
extern char *write_idx_file(char *index_name, struct pack_idx_entry **objects, int nr_objects, unsigned char *sha1);
extern int check_pack_crc(struct packed_git *p, struct pack_window **w_curs, off_t offset, off_t len, unsigned int nr);
extern int verify_pack(struct packed_git *);
-extern void fixup_pack_header_footer(int, unsigned char *, const char *, uint32_t);
+extern void fixup_pack_header_footer(int, unsigned char *, const char *, uint32_t, unsigned char *, off_t);
extern char *index_pack_lockfile(int fd);
#define PH_ERROR_EOF (-1)

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