Re: [Qemu-devel] [PATCH v2] 9pfs: fix integer overflow issue in xattr read/write

[Greg Kurz <groug@kaod.org>]

On Wed, 12 Oct 2016 19:53:39 -0700
Li Qiang <liq3ea@gmail.com> wrote:

> From: Li Qiang <liqiang6-s@360.cn>
> 
> In 9pfs xattr read/write function, it mix to use unsigned/signed
> ,32/64 bits integers. This will causes oob read/write issues. This patch
> fix this.
> 

I suggested a more detailed changelog.

> Signed-off-by: Li Qiang <liqiang6-s@360.cn>
> ---
>  hw/9pfs/9p.c | 34 +++++++++++++---------------------
>  hw/9pfs/9p.h |  4 ++--
>  2 files changed, 15 insertions(+), 23 deletions(-)
> 
> diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
> index e4040dc..8c7488f 100644
> --- a/hw/9pfs/9p.c
> +++ b/hw/9pfs/9p.c
> @@ -1642,20 +1642,17 @@ static int v9fs_xattr_read(V9fsState *s, V9fsPDU *pdu, V9fsFidState *fidp,
>  {
>      ssize_t err;
>      size_t offset = 7;
> -    int read_count;
> -    int64_t xattr_len;
> +    uint64_t read_count;
>      V9fsVirtioState *v = container_of(s, V9fsVirtioState, state);
>      VirtQueueElement *elem = v->elems[pdu->idx];
>  
> -    xattr_len = fidp->fs.xattr.len;
> -    read_count = xattr_len - off;
> +    if (fidp->fs.xattr.len < off) {
> +        read_count = 0;
> +    } else {
> +       read_count = fidp->fs.xattr.len - off;
> +    }
>      if (read_count > max_count) {
>          read_count = max_count;
> -    } else if (read_count < 0) {
> -        /*
> -         * read beyond XATTR value
> -         */
> -        read_count = 0;
>      }
>      err = pdu_marshal(pdu, offset, "d", read_count);
>      if (err < 0) {
> @@ -1982,23 +1979,18 @@ static int v9fs_xattr_write(V9fsState *s, V9fsPDU *pdu, V9fsFidState *fidp,
>  {
>      int i, to_copy;
>      ssize_t err = 0;
> -    int write_count;
> -    int64_t xattr_len;
> +    uint64_t write_count;
>      size_t offset = 7;
>  
>  
> -    xattr_len = fidp->fs.xattr.len;
> -    write_count = xattr_len - off;
> -    if (write_count > count) {
> -        write_count = count;
> -    } else if (write_count < 0) {
> -        /*
> -         * write beyond XATTR value len specified in
> -         * xattrcreate
> -         */
> +    if (fidp->fs.xattr.len < off) {
>          err = -ENOSPC;
>          goto out;
>      }
> +    write_count = fidp->fs.xattr.len - off;
> +    if (write_count > count) {
> +        write_count = count;
> +    }
>      err = pdu_marshal(pdu, offset, "d", write_count);
>      if (err < 0) {
>          return err;
> @@ -3254,7 +3246,7 @@ static void v9fs_xattrcreate(void *opaque)
>  {
>      int flags;
>      int32_t fid;
> -    int64_t size;
> +    uint64_t size;
>      ssize_t err = 0;
>      V9fsString name;
>      size_t offset = 7;
> diff --git a/hw/9pfs/9p.h b/hw/9pfs/9p.h
> index d539d2e..22198f6 100644
> --- a/hw/9pfs/9p.h
> +++ b/hw/9pfs/9p.h
> @@ -159,8 +159,8 @@ typedef struct V9fsConf
>  
>  typedef struct V9fsXattr
>  {
> -    int64_t copied_len;
> -    int64_t len;
> +    uint64_t copied_len;
> +    uint64_t len;

I had asked this to go to a separate patch... with the appropriate
justifications that these are byte counts and size_t/u64 in the guest.

>      void *value;
>      V9fsString name;
>      int flags;