[PATCH] erofs-utils: mkfs: fix out-of-bounds memory access in mt-mkfs

[Yifan Zhao]

If a segment is smaller than the block size, sizeof(sctx->membuf) should
be at least as large as the block size, as memory write into the buffer
is done in block size.

Signed-off-by: Yifan Zhao <zhaoyifan at sjtu.edu.cn>
---
 lib/compress.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/lib/compress.c b/lib/compress.c
index aeb7013..67a86db 100644
--- a/lib/compress.c
+++ b/lib/compress.c
@@ -1096,11 +1096,12 @@ void z_erofs_mt_workfn(struct erofs_work *work, void *tlsp)
 	struct erofs_compress_work *cwork = (struct erofs_compress_work *)work;
 	struct erofs_compress_wq_tls *tls = tlsp;
 	struct z_erofs_compress_sctx *sctx = &cwork->ctx;
+	struct erofs_sb_info *sbi = sctx->ictx->inode->sbi;
+	erofs_off_t blksz = erofs_blksiz(sbi);
 	int ret = 0;
 
-	ret = z_erofs_mt_wq_tls_init_compr(sctx->ictx->inode->sbi, tls,
-					   cwork->alg_id, cwork->alg_name,
-					   cwork->comp_level,
+	ret = z_erofs_mt_wq_tls_init_compr(sbi, tls, cwork->alg_id,
+					   cwork->alg_name, cwork->comp_level,
 					   cwork->dict_size);
 	if (ret)
 		goto out;
@@ -1109,7 +1110,7 @@ void z_erofs_mt_workfn(struct erofs_work *work, void *tlsp)
 	sctx->destbuf = tls->destbuf;
 	sctx->chandle = &tls->ccfg[cwork->alg_id].handle;
 
-	sctx->membuf = malloc(sctx->remaining);
+	sctx->membuf = malloc(max(blksz, sctx->remaining));
 	if (!sctx->membuf) {
 		ret = -ENOMEM;
 		goto out;
-- 
2.44.0