From f74cf18ad084a9185d8ae148d89265860aa8004c Mon Sep 17 00:00:00 2001 From: Lasse Collin Date: Thu, 3 Apr 2025 14:34:42 +0300 Subject: [PATCH 2/4] liblzma: mt dec: Simplify by removing the THR_STOP state The main thread can directly set THR_IDLE in threads_stop() which is called when errors are detected. threads_stop() won't return the stopped threads to the pool or free the memory pointed by thr->in anymore, but it doesn't matter because the existing workers won't be reused after an error. The resources will be cleaned up when threads_end() is called (reinitializing the decoder always calls threads_end()). Reviewed-by: Sebastian Andrzej Siewior Thanks-to: Sam James (cherry picked from commit c0c835964dfaeb2513a3c0bdb642105152fe9f34) CVE: CVE-2025-31115 Upstream-Status: Backport [https://github.com/tukaani-project/xz/commit/f74cf18ad084a9185d8ae148d89265860aa8004c] Signed-off-by: Peter Marko --- src/liblzma/common/stream_decoder_mt.c | 75 ++++++++++---------------- 1 file changed, 29 insertions(+), 46 deletions(-) diff --git a/src/liblzma/common/stream_decoder_mt.c b/src/liblzma/common/stream_decoder_mt.c index 6f06f1d1..e1d07007 100644 --- a/src/liblzma/common/stream_decoder_mt.c +++ b/src/liblzma/common/stream_decoder_mt.c @@ -23,15 +23,10 @@ typedef enum { THR_IDLE, /// Decoding is in progress. - /// Main thread may change this to THR_STOP or THR_EXIT. + /// Main thread may change this to THR_IDLE or THR_EXIT. /// The worker thread may change this to THR_IDLE. THR_RUN, - /// The main thread wants the thread to stop whatever it was doing - /// but not exit. Main thread may change this to THR_EXIT. - /// The worker thread may change this to THR_IDLE. - THR_STOP, - /// The main thread wants the thread to exit. THR_EXIT, @@ -346,27 +341,6 @@ worker_enable_partial_update(void *thr_ptr) } -/// Things do to at THR_STOP or when finishing a Block. -/// This is called with thr->coder->mutex locked. -static void -worker_stop(struct worker_thread *thr) -{ - // Update memory usage counters. - thr->coder->mem_in_use -= thr->in_size; - thr->in_size = 0; // thr->in was freed above. - - thr->coder->mem_in_use -= thr->mem_filters; - thr->coder->mem_cached += thr->mem_filters; - - // Put this thread to the stack of free threads. - thr->next = thr->coder->threads_free; - thr->coder->threads_free = thr; - - mythread_cond_signal(&thr->coder->cond); - return; -} - - static MYTHREAD_RET_TYPE worker_decoder(void *thr_ptr) { @@ -397,17 +371,6 @@ next_loop_unlocked: return MYTHREAD_RET_VALUE; } - if (thr->state == THR_STOP) { - thr->state = THR_IDLE; - mythread_mutex_unlock(&thr->mutex); - - mythread_sync(thr->coder->mutex) { - worker_stop(thr); - } - - goto next_loop_lock; - } - assert(thr->state == THR_RUN); // Update progress info for get_progress(). @@ -510,7 +473,22 @@ next_loop_unlocked: && thr->coder->thread_error == LZMA_OK) thr->coder->thread_error = ret; - worker_stop(thr); + // Return the worker thread to the stack of available + // threads. + { + // Update memory usage counters. + thr->coder->mem_in_use -= thr->in_size; + thr->in_size = 0; // thr->in was freed above. + + thr->coder->mem_in_use -= thr->mem_filters; + thr->coder->mem_cached += thr->mem_filters; + + // Put this thread to the stack of free threads. + thr->next = thr->coder->threads_free; + thr->coder->threads_free = thr; + } + + mythread_cond_signal(&thr->coder->cond); } goto next_loop_lock; @@ -544,17 +522,22 @@ threads_end(struct lzma_stream_coder *coder, const lzma_allocator *allocator) } +/// Tell worker threads to stop without doing any cleaning up. +/// The clean up will be done when threads_exit() is called; +/// it's not possible to reuse the threads after threads_stop(). +/// +/// This is called before returning an unrecoverable error code +/// to the application. It would be waste of processor time +/// to keep the threads running in such a situation. static void threads_stop(struct lzma_stream_coder *coder) { for (uint32_t i = 0; i < coder->threads_initialized; ++i) { + // The threads that are in the THR_RUN state will stop + // when they check the state the next time. There's no + // need to signal coder->threads[i].cond. mythread_sync(coder->threads[i].mutex) { - // The state must be changed conditionally because - // THR_IDLE -> THR_STOP is not a valid state change. - if (coder->threads[i].state != THR_IDLE) { - coder->threads[i].state = THR_STOP; - mythread_cond_signal(&coder->threads[i].cond); - } + coder->threads[i].state = THR_IDLE; } } @@ -1948,7 +1931,7 @@ stream_decoder_mt_init(lzma_next_coder *next, const lzma_allocator *allocator, // accounting from scratch, too. Changes in filter and block sizes may // affect number of threads. // - // FIXME? Reusing should be easy but unlike the single-threaded + // Reusing threads doesn't seem worth it. Unlike the single-threaded // decoder, with some types of input file combinations reusing // could leave quite a lot of memory allocated but unused (first // file could allocate a lot, the next files could use fewer