I ended up adding:
int ckpt_read_payload(ctx, void **ptr, int max, int type)
It returns the length of the payload actually read and allocated; caller
should free the buffer.
and:
char *ckpt_read_string(ctx, max)
It reads the payload of size up to @max (including terminating null!)
into allocated buffer that the caller should free. It returns this
buffer.
To play it safe, it forces a '\0' at the end of the buffer, in case
a malicious user didn't provide it. This way, the caller can safely
assume that it is indeed a null terminated string.
This is slightly different than your prototype, so you need to
update the fifth patch.
Oren.
Dan Smith wrote:
> Add a ckpt_read_string() function to allow reading of a variable-length
> (but length-capped) string from the checkpoint stream.
>
> Changes in v3:
> - Return immediately on allocation failure instead of falling through to the
> inevitable crash
>
> Changes in v2:
> - Avoid memcpy() by reading into the allocated buffer directly
>
> Acked-by: Serge Hallyn <serue@xxxxxxxxxx>
> Signed-off-by: Dan Smith <danms@xxxxxxxxxx>
> ---
> checkpoint/restart.c | 36 ++++++++++++++++++++++++++++++++++++
> include/linux/checkpoint.h | 1 +
> 2 files changed, 37 insertions(+), 0 deletions(-)
>
> diff --git a/checkpoint/restart.c b/checkpoint/restart.c
> index 65cafd9..b1ffc54 100644
> --- a/checkpoint/restart.c
> +++ b/checkpoint/restart.c
> @@ -285,6 +285,42 @@ int ckpt_read_consume(struct ckpt_ctx *ctx, int len, int type)
> return ret;
> }
>
> +/**
> + * ckpt_read_string - read a string (variable length)
> + * @ctx: checkpoint context
> + * @str: pointer to buffer to store allocated string (caller must kfree())
> + * @max: maximum acceptable length
> + *
> + * This can be used to read a variable-length string from the checkpoint
> + * stream. @max limits the size of the resulting buffer. Returns zero on
> + * success, negative on failure.
> + */
> +int ckpt_read_string(struct ckpt_ctx *ctx, char **str, int max)
> +{
> + int len;
> + int ret = 0;
> +
> + *str = NULL;
> +
> + len = _ckpt_read_obj_type(ctx, NULL, 0, CKPT_HDR_STRING);
> + if (len < 0)
> + return len;
> + else if (len > max)
> + return -EINVAL;
> +
> + *str = kzalloc(len + 1, GFP_KERNEL);
> + if (!*str)
> + return -ENOMEM;
> +
> + ret = ckpt_kread(ctx, *str, len);
> + if (ret < 0) {
> + kfree(*str);
> + *str = NULL;
> + }
> +
> + return ret;
> +}
> +
> /***********************************************************************
> * Restart
> */
> diff --git a/include/linux/checkpoint.h b/include/linux/checkpoint.h
> index 87b683b..a6935b3 100644
> --- a/include/linux/checkpoint.h
> +++ b/include/linux/checkpoint.h
> @@ -68,6 +68,7 @@ extern int _ckpt_read_obj_type(struct ckpt_ctx *ctx,
> extern int _ckpt_read_nbuffer(struct ckpt_ctx *ctx, void *ptr, int len);
> extern int _ckpt_read_buffer(struct ckpt_ctx *ctx, void *ptr, int len);
> extern int _ckpt_read_string(struct ckpt_ctx *ctx, void *ptr, int len);
> +extern int ckpt_read_string(struct ckpt_ctx *ctx, char **str, int max);
> extern void *ckpt_read_obj_type(struct ckpt_ctx *ctx, int len, int type);
> extern void *ckpt_read_buf_type(struct ckpt_ctx *ctx, int len, int type);
> extern int ckpt_read_consume(struct ckpt_ctx *ctx, int len, int type);
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