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Speed-up chunk list operations.

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The chunk list only has two operations: append and set
to one element. The two operations are split and the append
one is sped up by storing the last element.
Corrupted data could make a very long list to search through.

BUG=oss-fuzz:9190

Change-Id: I1aa813ca629df29efaa3b46dbd4c4c42dbeaa34c
This commit is contained in:
Vincent Rabaud
2018-07-03 16:36:34 +02:00
parent 2281bbf6f7
commit a9ceda7ff1
4 changed files with 54 additions and 46 deletions
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45
src/mux/muxinternal.c
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@@ -111,27 +111,6 @@ WebPChunk* ChunkSearchList(WebPChunk* first, uint32_t nth, uint32_t tag) {
return ((nth > 0) && (iter > 0)) ? NULL : first;
}
// Outputs a pointer to 'prev_chunk->next_',
// where 'prev_chunk' is the pointer to the chunk at position (nth - 1).
// Returns true if nth chunk was found.
static int ChunkSearchListToSet(WebPChunk** chunk_list, uint32_t nth,
WebPChunk*** const location) {
uint32_t count = 0;
assert(chunk_list != NULL);
*location = chunk_list;
while (*chunk_list != NULL) {
WebPChunk* const cur_chunk = *chunk_list;
++count;
if (count == nth) return 1; // Found.
chunk_list = &cur_chunk->next_;
*location = chunk_list;
}
// *chunk_list is ok to be NULL if adding at last location.
return (nth == 0 || (count == nth - 1)) ? 1 : 0;
}
//------------------------------------------------------------------------------
// Chunk writer methods.
@@ -156,11 +135,12 @@ WebPMuxError ChunkAssignData(WebPChunk* chunk, const WebPData* const data,
return WEBP_MUX_OK;
}
WebPMuxError ChunkSetNth(WebPChunk* chunk, WebPChunk** chunk_list,
uint32_t nth) {
WebPMuxError ChunkSetHead(WebPChunk* const chunk,
WebPChunk** const chunk_list) {
WebPChunk* new_chunk;
if (!ChunkSearchListToSet(chunk_list, nth, &chunk_list)) {
assert(chunk_list != NULL);
if (*chunk_list != NULL) {
return WEBP_MUX_NOT_FOUND;
}
@@ -168,11 +148,26 @@ WebPMuxError ChunkSetNth(WebPChunk* chunk, WebPChunk** chunk_list,
if (new_chunk == NULL) return WEBP_MUX_MEMORY_ERROR;
*new_chunk = *chunk;
chunk->owner_ = 0;
new_chunk->next_ = *chunk_list;
new_chunk->next_ = NULL;
*chunk_list = new_chunk;
return WEBP_MUX_OK;
}
WebPMuxError ChunkAppend(WebPChunk* const chunk,
WebPChunk*** const chunk_list) {
assert(chunk_list != NULL && *chunk_list != NULL);
if (**chunk_list == NULL) {
ChunkSetHead(chunk, *chunk_list);
} else {
WebPChunk* last_chunk = **chunk_list;
while (last_chunk->next_ != NULL) last_chunk = last_chunk->next_;
ChunkSetHead(chunk, &last_chunk->next_);
*chunk_list = &last_chunk->next_;
}
return WEBP_MUX_OK;
}
//------------------------------------------------------------------------------
// Chunk deletion method(s).