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journal/compress: fix zstd decompression with capped output size 

decompress_blob_zstd() would allocate ever bigger buffers in a loop trying to
get a buffer big enough to decompress the input data. This is wasteful, since
we can just query the size of the decompressed data from the compressed header.
Worse, it doesn't work when the output size is capped, i.e. when dst_max != 0.
If the decompressed blob happened to be bigger than dst_max, decompression
would fail with -ENOBUFS. We need to use "stream decompression" instead, and
only get min(uncompressed size, dst_max) bytes of output.

Fixes https://bugzilla.redhat.com/show_bug.cgi?id=1856037 in a second way.
This commit is contained in:
Zbigniew Jędrzejewski-Szmek 2020-07-18 21:39:03 +02:00
parent b4a11ca3f2
commit a24153279e
1 changed files with 30 additions and 28 deletions
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58
src/journal/compress.c
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@ -259,10 +259,10 @@ int decompress_blob_lz4(const void *src, uint64_t src_size,
int decompress_blob_zstd(
const void *src, uint64_t src_size,
void **dst, size_t *dst_alloc_size, size_t* dst_size, size_t dst_max) {
void **dst, size_t *dst_alloc_size, size_t *dst_size, size_t dst_max) {
#if HAVE_ZSTD
size_t space;
uint64_t size;
assert(src);
assert(src_size > 0);
@ -271,38 +271,40 @@ int decompress_blob_zstd(
assert(dst_size);
assert(*dst_alloc_size == 0 || *dst);
if (src_size > SIZE_MAX/2) /* Overflow? */
return -ENOBUFS;
space = src_size * 2;
if (dst_max > 0 && space > dst_max)
space = dst_max;
size = ZSTD_getFrameContentSize(src, src_size);
if (IN_SET(size, ZSTD_CONTENTSIZE_ERROR, ZSTD_CONTENTSIZE_UNKNOWN))
return -EBADMSG;
if (!greedy_realloc(dst, dst_alloc_size, space, 1))
if (dst_max > 0 && size > dst_max)
size = dst_max;
if (size > SIZE_MAX)
return -E2BIG;
if (!(greedy_realloc(dst, dst_alloc_size, MAX(ZSTD_DStreamOutSize(), size), 1)))
return -ENOMEM;
for (;;) {
size_t k;
_cleanup_(ZSTD_freeDCtxp) ZSTD_DCtx *dctx = ZSTD_createDCtx();
if (!dctx)
return -ENOMEM;
k = ZSTD_decompress(*dst, *dst_alloc_size, src, src_size);
if (!ZSTD_isError(k)) {
*dst_size = k;
return 0;
}
if (ZSTD_getErrorCode(k) != ZSTD_error_dstSize_tooSmall)
return zstd_ret_to_errno(k);
ZSTD_inBuffer input = {
.src = src,
.size = src_size,
};
ZSTD_outBuffer output = {
.dst = *dst,
.size = *dst_alloc_size,
};
if (dst_max > 0 && space >= dst_max) /* Already at max? */
return -ENOBUFS;
if (space > SIZE_MAX / 2) /* Overflow? */
return -ENOBUFS;
space *= 2;
if (dst_max > 0 && space > dst_max)
space = dst_max;
if (!greedy_realloc(dst, dst_alloc_size, space, 1))
return -ENOMEM;
size_t k = ZSTD_decompressStream(dctx, &output, &input);
if (ZSTD_isError(k)) {
log_debug("ZSTD decoder failed: %s", ZSTD_getErrorName(k));
return zstd_ret_to_errno(k);
}
assert(output.pos >= size);
*dst_size = size;
return 0;
#else
return -EPROTONOSUPPORT;
#endif