On Fri, Mar 17, 2017 at 03:39:10PM +0100, Greg Kurz wrote:
> Replies from the virtfs proxy are made up of a fixed-size header (8 bytes)
> and a payload of variable size (maximum 64kb). When receiving a reply,
> the proxy backend first reads the whole header and then unmarshals it.
> If the header is okay, it then does the same operation with the payload.
>
> Since the proxy backend uses a pre-allocated buffer which has enough room
> for a header and the maximum payload size, marshalling should never fail
> with fixed size arguments. Any error here is likely to result from a more
> serious corruption in QEMU and we'd better dump core right away.
>
> This patch adds error checks where they are missing and converts the
> associated error paths into assertions.
>
> Note that we don't want to use sizeof() in the checks since the value
> we want to use depends on the format rather than the size of the buffer.
> Short marshal formats can be handled with numerical values. Size macros
> are introduced for bigger ones (ProxyStat and ProxyStatFS).
>
> This should also address Coverity's complaints CID 1348519 and CID 1348520,
> about not always checking the return value of proxy_unmarshal().
>
> Signed-off-by: Greg Kurz <gr...@kaod.org>
> ---
> v2: - added PROXY_STAT_SZ and PROXY_STATFS_SZ macros
> - updated changelog
> ---
> hw/9pfs/9p-proxy.c | 24 +++++++++++++-----------
> hw/9pfs/9p-proxy.h | 10 ++++++++--
> 2 files changed, 21 insertions(+), 13 deletions(-)
>
> diff --git a/hw/9pfs/9p-proxy.c b/hw/9pfs/9p-proxy.c
> index f4aa7a9d70f8..363bea66035e 100644
> --- a/hw/9pfs/9p-proxy.c
> +++ b/hw/9pfs/9p-proxy.c
> @@ -165,7 +165,8 @@ static int v9fs_receive_response(V9fsProxy *proxy, int
> type,
> return retval;
> }
> reply->iov_len = PROXY_HDR_SZ;
> - proxy_unmarshal(reply, 0, "dd", &header.type, &header.size);
> + retval = proxy_unmarshal(reply, 0, "dd", &header.type, &header.size);
> + assert(retval == 8);
> /*
> * if response size > PROXY_MAX_IO_SZ, read the response but ignore it
> and
> * return -ENOBUFS
> @@ -194,15 +195,14 @@ static int v9fs_receive_response(V9fsProxy *proxy, int
> type,
> if (header.type == T_ERROR) {
> int ret;
> ret = proxy_unmarshal(reply, PROXY_HDR_SZ, "d", status);
> - if (ret < 0) {
> - *status = ret;
> - }
> + assert(ret == 4);
> return 0;
> }
>
> switch (type) {
> case T_LSTAT: {
> ProxyStat prstat;
> + QEMU_BUILD_BUG_ON(sizeof(prstat) != PROXY_STAT_SZ);
I'd just put this assert at the struct declaration
..snip...
> diff --git a/hw/9pfs/9p-proxy.h b/hw/9pfs/9p-proxy.h
> index b84301d001b0..918c45016a3c 100644
> --- a/hw/9pfs/9p-proxy.h
> +++ b/hw/9pfs/9p-proxy.h
> @@ -79,7 +79,10 @@ typedef struct {
> uint64_t st_mtim_nsec;
> uint64_t st_ctim_sec;
> uint64_t st_ctim_nsec;
> -} ProxyStat;
> +} QEMU_PACKED ProxyStat;
> +
> +#define PROXY_STAT_SZ \
> + (8 + 8 + 8 + 4 + 4 + 4 + 8 + 8 + 8 + 8 + 8 + 8 + 8 + 8 + 8 + 8)
eg.
QEMU_BUILD_BUG_ON(sizeof(ProxyStat) !=
(8 + 8 + 8 + 4 + 4 + 4 + 8 + 8 + 8 + 8 + 8 + 8 + 8 + 8 + 8 + 8));
Regards,
Daniel
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