erofs-utils: lib: switch to on-heap fitblk_buffer for libzstd
- Allocating VLAs on the stack (or using alloca()) for large sizes
could exceed the stack limit;
- It's easier to isolate these buffers on the heap for code sanitizers
to detect potential bugs.
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20250703053446.201941-1-hsiangkao@linux.alibaba.com
diff --git a/lib/compressor_libzstd.c b/lib/compressor_libzstd.c
index 223806e..de04c58 100644
--- a/lib/compressor_libzstd.c
+++ b/lib/compressor_libzstd.c
@@ -4,20 +4,34 @@
#include "erofs/config.h"
#include <zstd.h>
#include <zstd_errors.h>
-#include <alloca.h>
+#include <stdlib.h>
#include "compressor.h"
#include "erofs/atomic.h"
+struct erofs_libzstd_context {
+ ZSTD_CCtx *cctx;
+ u8 *fitblk_buffer;
+ unsigned int fitblk_bufsiz;
+};
+
static int libzstd_compress_destsize(const struct erofs_compress *c,
const void *src, unsigned int *srcsize,
void *dst, unsigned int dstsize)
{
- ZSTD_CCtx *cctx = c->private_data;
+ struct erofs_libzstd_context *ctx = c->private_data;
size_t l = 0; /* largest input that fits so far */
size_t l_csize = 0;
size_t r = *srcsize + 1; /* smallest input that doesn't fit so far */
size_t m;
- u8 *fitblk_buffer = alloca(dstsize + 32);
+
+ if (dstsize + 32 > ctx->fitblk_bufsiz) {
+ u8 *buf = realloc(ctx->fitblk_buffer, dstsize + 32);
+
+ if (!buf)
+ return -ENOMEM;
+ ctx->fitblk_bufsiz = dstsize + 32;
+ ctx->fitblk_buffer = buf;
+ }
m = dstsize * 4;
for (;;) {
@@ -26,7 +40,7 @@
m = max(m, l + 1);
m = min(m, r - 1);
- csize = ZSTD_compress2(cctx, fitblk_buffer,
+ csize = ZSTD_compress2(ctx->cctx, ctx->fitblk_buffer,
dstsize + 32, src, m);
if (ZSTD_isError(csize)) {
if (ZSTD_getErrorCode(csize) == ZSTD_error_dstSize_tooSmall)
@@ -36,7 +50,7 @@
if (csize > 0 && csize <= dstsize) {
/* Fits */
- memcpy(dst, fitblk_buffer, csize);
+ memcpy(dst, ctx->fitblk_buffer, csize);
l = m;
l_csize = csize;
if (r <= l + 1 || csize + 1 >= dstsize)
@@ -61,9 +75,14 @@
static int compressor_libzstd_exit(struct erofs_compress *c)
{
- if (!c->private_data)
+ struct erofs_libzstd_context *ctx = c->private_data;
+
+ if (!ctx)
return -EINVAL;
- ZSTD_freeCCtx(c->private_data);
+
+ free(ctx->fitblk_buffer);
+ ZSTD_freeCCtx(ctx->cctx);
+ free(ctx);
return 0;
}
@@ -101,27 +120,41 @@
static int compressor_libzstd_init(struct erofs_compress *c)
{
+ struct erofs_libzstd_context *ctx = c->private_data;
static erofs_atomic_bool_t __warnonce;
- ZSTD_CCtx *cctx = c->private_data;
- size_t err;
+ ZSTD_CCtx *cctx;
+ size_t errcode;
+ int err;
- ZSTD_freeCCtx(cctx);
+ if (ctx) {
+ ZSTD_freeCCtx(ctx->cctx);
+ ctx->cctx = NULL;
+ c->private_data = NULL;
+ } else {
+ ctx = calloc(1, sizeof(*ctx));
+ if (!ctx)
+ return -ENOMEM;
+ }
cctx = ZSTD_createCCtx();
- if (!cctx)
- return -ENOMEM;
+ if (!cctx) {
+ err = -ENOMEM;
+ goto out_err;
+ }
- err = ZSTD_CCtx_setParameter(cctx, ZSTD_c_compressionLevel, c->compression_level);
- if (ZSTD_isError(err)) {
+ err = -EINVAL;
+ errcode = ZSTD_CCtx_setParameter(cctx, ZSTD_c_compressionLevel, c->compression_level);
+ if (ZSTD_isError(errcode)) {
erofs_err("failed to set compression level: %s",
- ZSTD_getErrorName(err));
- return -EINVAL;
+ ZSTD_getErrorName(errcode));
+ goto out_err;
}
- err = ZSTD_CCtx_setParameter(cctx, ZSTD_c_windowLog, ilog2(c->dict_size));
- if (ZSTD_isError(err)) {
- erofs_err("failed to set window log: %s", ZSTD_getErrorName(err));
- return -EINVAL;
+ errcode = ZSTD_CCtx_setParameter(cctx, ZSTD_c_windowLog, ilog2(c->dict_size));
+ if (ZSTD_isError(errcode)) {
+ erofs_err("failed to set window log: %s", ZSTD_getErrorName(errcode));
+ goto out_err;
}
- c->private_data = cctx;
+ ctx->cctx = cctx;
+ c->private_data = ctx;
if (!erofs_atomic_test_and_set(&__warnonce)) {
erofs_warn("EXPERIMENTAL libzstd compressor in use. Note that `fitblk` isn't supported by upstream zstd for now.");
@@ -129,6 +162,10 @@
erofs_info("You could clarify further needs in zstd repository <https://github.com/facebook/zstd/issues> for reference too.");
}
return 0;
+out_err:
+ ZSTD_freeCCtx(cctx);
+ free(ctx);
+ return err;
}
const struct erofs_compressor erofs_compressor_libzstd = {
