Re: [Qemu-trivial] [PATCH 6/9] 9pfs: fix memory leak

[Michael Tokarev <mjt@tls.msk.ru>]

27.02.2015 10:50, arei.gonglei@huawei.com wrote:
> From: Gonglei <arei.gonglei@huawei.com>
> 
> Signed-off-by: Gonglei <arei.gonglei@huawei.com>
> ---
>  hw/9pfs/virtio-9p-local.c | 10 ++--------
>  1 file changed, 2 insertions(+), 8 deletions(-)
> 
> diff --git a/hw/9pfs/virtio-9p-local.c b/hw/9pfs/virtio-9p-local.c
> index a183eee..bcad4e0 100644
> --- a/hw/9pfs/virtio-9p-local.c
> +++ b/hw/9pfs/virtio-9p-local.c
> @@ -500,7 +500,6 @@ static int local_mknod(FsContext *fs_ctx, V9fsPath *dir_path,
>          buffer = rpath(fs_ctx, path);
>          err = mknod(buffer, SM_LOCAL_MODE_BITS|S_IFREG, 0);
>          if (err == -1) {
> -            g_free(buffer);
>              goto out;
>          }
>          err = local_set_xattr(buffer, credp);
> @@ -513,7 +512,6 @@ static int local_mknod(FsContext *fs_ctx, V9fsPath *dir_path,
>          buffer = rpath(fs_ctx, path);
>          err = mknod(buffer, SM_LOCAL_MODE_BITS|S_IFREG, 0);
>          if (err == -1) {
> -            g_free(buffer);
>              goto out;
>          }
>          err = local_set_mapped_file_attr(fs_ctx, path, credp);
> @@ -526,7 +524,6 @@ static int local_mknod(FsContext *fs_ctx, V9fsPath *dir_path,
>          buffer = rpath(fs_ctx, path);
>          err = mknod(buffer, credp->fc_mode, credp->fc_rdev);
>          if (err == -1) {
> -            g_free(buffer);
>              goto out;
>          }
>          err = local_post_create_passthrough(fs_ctx, path, credp);
> @@ -540,8 +537,8 @@ static int local_mknod(FsContext *fs_ctx, V9fsPath *dir_path,
>  err_end:
>      remove(buffer);
>      errno = serrno;
> -    g_free(buffer);
>  out:
> +    g_free(buffer);
>      v9fs_string_free(&fullname);
>      return err;
>  }
> @@ -676,7 +673,6 @@ static int local_open2(FsContext *fs_ctx, V9fsPath *dir_path, const char *name,
>          buffer = rpath(fs_ctx, path);
>          fd = open(buffer, flags, SM_LOCAL_MODE_BITS);
>          if (fd == -1) {
> -            g_free(buffer);
>              err = fd;
>              goto out;
>          }
> @@ -691,7 +687,6 @@ static int local_open2(FsContext *fs_ctx, V9fsPath *dir_path, const char *name,
>          buffer = rpath(fs_ctx, path);
>          fd = open(buffer, flags, SM_LOCAL_MODE_BITS);
>          if (fd == -1) {
> -            g_free(buffer);
>              err = fd;
>              goto out;
>          }
> @@ -707,7 +702,6 @@ static int local_open2(FsContext *fs_ctx, V9fsPath *dir_path, const char *name,
>          buffer = rpath(fs_ctx, path);
>          fd = open(buffer, flags, credp->fc_mode);
>          if (fd == -1) {
> -            g_free(buffer);
>              err = fd;
>              goto out;
>          }
> @@ -725,8 +719,8 @@ err_end:
>      close(fd);
>      remove(buffer);
>      errno = serrno;
> -    g_free(buffer);
>  out:
> +    g_free(buffer);
>      v9fs_string_free(&fullname);
>      return err;
>  }

This patch introduces a compiler warning, which is technically
correct:

hw/9pfs/virtio-9p-local.c: In function ‘local_open2’:
hw/9pfs/virtio-9p-local.c:723:5: error: ‘buffer’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
     g_free(buffer);
     ^
hw/9pfs/virtio-9p-local.c: In function ‘local_mknod’:
hw/9pfs/virtio-9p-local.c:541:5: error: ‘buffer’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
     g_free(buffer);
     ^

This is because `buffer' variable is initialized within one
of the `if' branches but is left uninitialized if none of
the conditions is true.  In reality this can't happen because
at least one condition is always true.

It is a one more reason to rewrite this code like I mentioned
in another mail instead of trying to fix random issues like
this.  I'll try to come up with a patch doing that shortly.
Meanwhile I'll drop this patch.

Thanks,

/mjt