Re: [PATCH] xfs: avoid null *src in memcpy call in xlog_write

Bill O'Donnell
2015-10-07T16:48:56Z

Looks good to me.

Reviewed-by: Bill O'Donnell <billodo@redhat.com>

On Wed, Oct 07, 2015 at 11:33:43AM -0500, Eric Sandeen wrote:
> The gcc undefined behavior sanitizer caught this; surely
> any sane memcpy implementation will no-op if size == 0,
> but behavior with a *src of NULL is technically undefined
> (declared nonnull), so avoid it here.
>
> We are actually in this situation frequently via
> xlog_commit_record(), because:
>
> struct xfs_log_iovec reg = {
> .i_addr = NULL,
> .i_len = 0,
> .i_type = XLOG_REG_TYPE_COMMIT,
> };
>
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
> ---
>
> diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
> index 4012523..8897fd1 100644
> --- a/fs/xfs/xfs_log.c
> +++ b/fs/xfs/xfs_log.c
> @@ -2424,7 +2424,10 @@ xlog_write(
>
> /* copy region */
> ASSERT(copy_len >= 0);
> - memcpy(ptr, reg->i_addr + copy_off, copy_len);
> + ASSERT(reg->i_addr + copy_off > 0 || copy_len == 0);
> + /* size == 0 is ok, but *src == NULL is undefined */
> + if (reg->i_addr + copy_off)
> + memcpy(ptr, reg->i_addr + copy_off, copy_len);
> xlog_write_adv_cnt(&ptr, &len, &log_offset, copy_len);
>
> copy_len += start_rec_copy + sizeof(xlog_op_header_t);
>
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