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Re: [PATCH 2/4] block/vvfat: Fix leak of BDRVVVFATState::used_clusters

From: Stefano Garzarella
Subject: Re: [PATCH 2/4] block/vvfat: Fix leak of BDRVVVFATState::used_clusters
Date: Mon, 3 May 2021 15:24:24 +0200

On Fri, Apr 30, 2021 at 06:25:17PM +0200, Philippe Mathieu-Daudé wrote:
used_clusters is allocated in enable_write_target(), called by
vvfat_open(), but never free'd.
Allocate it using GLib API, and free it in vvfat_close().

This fixes (QEMU built with --enable-sanitizers):

 Direct leak of 64508 byte(s) in 1 object(s) allocated from:
     #0 0x55d7a36378f7 in calloc (qemu-system-x86_64+0x1dab8f7)
     #1 0x55d7a5e14246 in enable_write_target block/vvfat.c:3145:24
     #2 0x55d7a5e123aa in vvfat_open block/vvfat.c:1236:19
     #3 0x55d7a5a5363f in bdrv_open_driver block.c:1526:15
     #4 0x55d7a5a9d369 in bdrv_open_common block.c:1802:11
     #5 0x55d7a5a609f1 in bdrv_open_inherit block.c:3444:11
     #6 0x55d7a5a65411 in bdrv_open_child_bs block.c:3079:10
     #7 0x55d7a5a60079 in bdrv_open_inherit block.c:3391:19
     #8 0x55d7a5a65da3 in bdrv_open block.c:3537:12
     #9 0x55d7a5b33f6a in blk_new_open block/block-backend.c:421:10
     #10 0x55d7a5a0a33e in blockdev_init blockdev.c:610:15
     #11 0x55d7a5a088e7 in drive_new blockdev.c:994:11
     #12 0x55d7a51b10c4 in drive_init_func softmmu/vl.c:636:12
     #13 0x55d7a620e148 in qemu_opts_foreach util/qemu-option.c:1167:14
     #14 0x55d7a51b0e20 in configure_blockdev softmmu/vl.c:695:9
     #15 0x55d7a51a70b5 in qemu_create_early_backends softmmu/vl.c:1895:5
     #16 0x55d7a519bf87 in qemu_init softmmu/vl.c:3551:5
     #17 0x55d7a366f619 in main softmmu/main.c:49:5

Fixes: a046433a161 ("Major overhaul of the virtual FAT driver for read/write 
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
block/vvfat.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/block/vvfat.c b/block/vvfat.c
index 5a4a7915220..2cc21787600 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c
@@ -3142,7 +3142,7 @@ static int enable_write_target(BlockDriverState *bs, 
Error **errp)
    int size = sector2cluster(s, s->sector_count);
    QDict *options;

-    s->used_clusters = calloc(size, 1);
+    s->used_clusters = g_malloc0(size);

    array_init(&(s->commits), sizeof(commit_t));

@@ -3233,6 +3233,7 @@ static void vvfat_close(BlockDriverState *bs)
+    g_free(s->used_clusters);

    if (s->qcow) {

In vvfat_open() we set to NULL the other pointers allocated through GLib API (e.g. s->qcow_filename), but IIUC the BDRVVVFATState (bs->opaque) is allocated through g_malloc0() in bdrv_open_driver(), so those initializations should be superfluous and in this case we can avoid setting s->used_clusters to NULL.

Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>

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