Similar to the recursion in packed_object_info(), this leads to
problems on stack-space-constrained systems in the presence of long
delta chains.
We proceed in three phases:
1. Dig through the delta chain, saving each delta object's offsets and
size on an ad-hoc stack.
2. Unpack the base object at the bottom.
3. Unpack and apply the deltas from the stack.
Signed-off-by: Thomas Rast <trast@xxxxxxxxxxxxxxx>
---
sha1_file.c | 231 +++++++++++++++++++++++++++++++++++++++---------------------
1 file changed, 150 insertions(+), 81 deletions(-)
diff --git a/sha1_file.c b/sha1_file.c
index da41f51..f9191aa 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -1943,68 +1943,6 @@ static void add_delta_base_cache(struct packed_git *p, off_t base_offset,
static void *read_object(const unsigned char *sha1, enum object_type *type,
unsigned long *size);
-static void *unpack_delta_entry(struct packed_git *p,
- struct pack_window **w_curs,
- off_t curpos,
- unsigned long delta_size,
- off_t obj_offset,
- enum object_type *type,
- unsigned long *sizep)
-{
- void *delta_data, *result, *base;
- unsigned long base_size;
- off_t base_offset;
-
- base_offset = get_delta_base(p, w_curs, &curpos, *type, obj_offset);
- if (!base_offset) {
- error("failed to validate delta base reference "
- "at offset %"PRIuMAX" from %s",
- (uintmax_t)curpos, p->pack_name);
- return NULL;
- }
- unuse_pack(w_curs);
- base = cache_or_unpack_entry(p, base_offset, &base_size, type, 0);
- if (!base) {
- /*
- * We're probably in deep shit, but let's try to fetch
- * the required base anyway from another pack or loose.
- * This is costly but should happen only in the presence
- * of a corrupted pack, and is better than failing outright.
- */
- struct revindex_entry *revidx;
- const unsigned char *base_sha1;
- revidx = find_pack_revindex(p, base_offset);
- if (!revidx)
- return NULL;
- base_sha1 = nth_packed_object_sha1(p, revidx->nr);
- error("failed to read delta base object %s"
- " at offset %"PRIuMAX" from %s",
- sha1_to_hex(base_sha1), (uintmax_t)base_offset,
- p->pack_name);
- mark_bad_packed_object(p, base_sha1);
- base = read_object(base_sha1, type, &base_size);
- if (!base)
- return NULL;
- }
-
- delta_data = unpack_compressed_entry(p, w_curs, curpos, delta_size);
- if (!delta_data) {
- error("failed to unpack compressed delta "
- "at offset %"PRIuMAX" from %s",
- (uintmax_t)curpos, p->pack_name);
- free(base);
- return NULL;
- }
- result = patch_delta(base, base_size,
- delta_data, delta_size,
- sizep);
- if (!result)
- die("failed to apply delta");
- free(delta_data);
- add_delta_base_cache(p, base_offset, base, base_size, *type);
- return result;
-}
-
static void write_pack_access_log(struct packed_git *p, off_t obj_offset)
{
static FILE *log_file;
@@ -2025,48 +1963,179 @@ static void write_pack_access_log(struct packed_git *p, off_t obj_offset)
int do_check_packed_object_crc;
+#define UNPACK_ENTRY_STACK_PREALLOC 64
+struct unpack_entry_stack_ent {
+ off_t obj_offset;
+ off_t curpos;
+ unsigned long size;
+};
+
void *unpack_entry(struct packed_git *p, off_t obj_offset,
- enum object_type *type, unsigned long *sizep)
+ enum object_type *final_type, unsigned long *final_size)
{
struct pack_window *w_curs = NULL;
off_t curpos = obj_offset;
- void *data;
+ void *data = NULL;
+ unsigned long size;
+ enum object_type type;
+ struct unpack_entry_stack_ent small_delta_stack[UNPACK_ENTRY_STACK_PREALLOC];
+ struct unpack_entry_stack_ent *delta_stack = small_delta_stack;
+ int delta_stack_nr = 0, delta_stack_alloc = UNPACK_ENTRY_STACK_PREALLOC;
+ int base_from_cache = 0;
if (log_pack_access)
write_pack_access_log(p, obj_offset);
- if (do_check_packed_object_crc && p->index_version > 1) {
- struct revindex_entry *revidx = find_pack_revindex(p, obj_offset);
- unsigned long len = revidx[1].offset - obj_offset;
- if (check_pack_crc(p, &w_curs, obj_offset, len, revidx->nr)) {
- const unsigned char *sha1 =
- nth_packed_object_sha1(p, revidx->nr);
- error("bad packed object CRC for %s",
- sha1_to_hex(sha1));
- mark_bad_packed_object(p, sha1);
- unuse_pack(&w_curs);
- return NULL;
+ /* PHASE 1: drill down to the innermost base object */
+ for (;;) {
+ off_t base_offset;
+ int i;
+ struct delta_base_cache_entry *ent;
+
+ if (do_check_packed_object_crc && p->index_version > 1) {
+ struct revindex_entry *revidx = find_pack_revindex(p, obj_offset);
+ unsigned long len = revidx[1].offset - obj_offset;
+ if (check_pack_crc(p, &w_curs, obj_offset, len, revidx->nr)) {
+ const unsigned char *sha1 =
+ nth_packed_object_sha1(p, revidx->nr);
+ error("bad packed object CRC for %s",
+ sha1_to_hex(sha1));
+ mark_bad_packed_object(p, sha1);
+ unuse_pack(&w_curs);
+ return NULL;
+ }
+ }
+
+ ent = get_delta_base_cache_entry(p, curpos);
+ if (eq_delta_base_cache_entry(ent, p, curpos)) {
+ type = ent->type;
+ data = ent->data;
+ size = ent->size;
+ clear_delta_base_cache_entry(ent);
+ base_from_cache = 1;
+ break;
+ }
+
+ type = unpack_object_header(p, &w_curs, &curpos, &size);
+ if (type != OBJ_OFS_DELTA && type != OBJ_REF_DELTA)
+ break;
+
+ base_offset = get_delta_base(p, &w_curs, &curpos, type, obj_offset);
+ if (!base_offset) {
+ error("failed to validate delta base reference "
+ "at offset %"PRIuMAX" from %s",
+ (uintmax_t)curpos, p->pack_name);
+ /* bail to phase 2, in hopes of recovery */
+ data = NULL;
+ break;
}
+
+ /* push object, proceed to base */
+ if (delta_stack_nr >= delta_stack_alloc
+ && delta_stack == small_delta_stack) {
+ delta_stack_alloc = alloc_nr(delta_stack_nr);
+ delta_stack = xmalloc(sizeof(*delta_stack)*delta_stack_alloc);
+ memcpy(delta_stack, small_delta_stack,
+ sizeof(*delta_stack)*delta_stack_nr);
+ } else {
+ ALLOC_GROW(delta_stack, delta_stack_nr+1, delta_stack_alloc);
+ }
+ i = delta_stack_nr++;
+ delta_stack[i].obj_offset = obj_offset;
+ delta_stack[i].curpos = curpos;
+ delta_stack[i].size = size;
+
+ curpos = obj_offset = base_offset;
}
- *type = unpack_object_header(p, &w_curs, &curpos, sizep);
- switch (*type) {
+ /* PHASE 2: handle the base */
+ switch (type) {
case OBJ_OFS_DELTA:
case OBJ_REF_DELTA:
- data = unpack_delta_entry(p, &w_curs, curpos, *sizep,
- obj_offset, type, sizep);
+ if (data)
+ die("BUG in unpack_entry: left loop at a valid delta");
break;
case OBJ_COMMIT:
case OBJ_TREE:
case OBJ_BLOB:
case OBJ_TAG:
- data = unpack_compressed_entry(p, &w_curs, curpos, *sizep);
+ if (!base_from_cache)
+ data = unpack_compressed_entry(p, &w_curs, curpos, size);
break;
default:
data = NULL;
error("unknown object type %i at offset %"PRIuMAX" in %s",
- *type, (uintmax_t)obj_offset, p->pack_name);
+ type, (uintmax_t)obj_offset, p->pack_name);
}
+
+ /* PHASE 3: apply deltas in order */
+
+ /* invariants:
+ * 'data' holds the base data, or NULL if there was corruption
+ */
+ while (delta_stack_nr) {
+ void *delta_data;
+ void *base = data;
+ unsigned long delta_size, base_size = size;
+ int i;
+
+ data = NULL;
+
+ if (base)
+ add_delta_base_cache(p, obj_offset, base, base_size, type);
+
+ if (!base) {
+ /*
+ * We're probably in deep shit, but let's try to fetch
+ * the required base anyway from another pack or loose.
+ * This is costly but should happen only in the presence
+ * of a corrupted pack, and is better than failing outright.
+ */
+ struct revindex_entry *revidx;
+ const unsigned char *base_sha1;
+ revidx = find_pack_revindex(p, obj_offset);
+ if (revidx) {
+ base_sha1 = nth_packed_object_sha1(p, revidx->nr);
+ error("failed to read delta base object %s"
+ " at offset %"PRIuMAX" from %s",
+ sha1_to_hex(base_sha1), (uintmax_t)obj_offset,
+ p->pack_name);
+ mark_bad_packed_object(p, base_sha1);
+ base = read_object(base_sha1, &type, &base_size);
+ }
+ }
+
+ i = --delta_stack_nr;
+ obj_offset = delta_stack[i].obj_offset;
+ curpos = delta_stack[i].curpos;
+ delta_size = delta_stack[i].size;
+
+ if (!base)
+ continue;
+
+ delta_data = unpack_compressed_entry(p, &w_curs, curpos, delta_size);
+
+ if (!delta_data) {
+ error("failed to unpack compressed delta "
+ "at offset %"PRIuMAX" from %s",
+ (uintmax_t)curpos, p->pack_name);
+ free(base);
+ data = NULL;
+ continue;
+ }
+
+ data = patch_delta(base, base_size,
+ delta_data, delta_size,
+ &size);
+ if (!data)
+ die("failed to apply delta");
+
+ free (delta_data);
+ }
+
+ *final_type = type;
+ *final_size = size;
+
unuse_pack(&w_curs);
return data;
}
--
1.8.2.344.g1440b22
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