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SubjectRe: [PATCH] ovl: Use "buf" flexible array for memcpy() destination
On Sat, Sep 24, 2022 at 12:33:15AM -0700, Kees Cook wrote:
> The "buf" flexible array needs to be the memcpy() destination to avoid
> false positive run-time warning from the recent FORTIFY_SOURCE
> hardening:
>
> memcpy: detected field-spanning write (size 93) of single field "&fh->fb" at fs/overlayfs/export.c:799 (size 21)
>
> Cc: Miklos Szeredi <miklos@szeredi.hu>
> Cc: linux-unionfs@vger.kernel.org
> Reported-by: syzbot+9d14351a171d0d1c7955@syzkaller.appspotmail.com
> Link: https://lore.kernel.org/all/000000000000763a6c05e95a5985@google.com/
> Signed-off-by: Kees Cook <keescook@chromium.org>

Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Thanks!
--
Gustavo

> ---
> fs/overlayfs/export.c | 2 +-
> fs/overlayfs/overlayfs.h | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/overlayfs/export.c b/fs/overlayfs/export.c
> index e065a5b9a442..ac9c3ad04016 100644
> --- a/fs/overlayfs/export.c
> +++ b/fs/overlayfs/export.c
> @@ -796,7 +796,7 @@ static struct ovl_fh *ovl_fid_to_fh(struct fid *fid, int buflen, int fh_type)
> return ERR_PTR(-ENOMEM);
>
> /* Copy unaligned inner fh into aligned buffer */
> - memcpy(&fh->fb, fid, buflen - OVL_FH_WIRE_OFFSET);
> + memcpy(fh->buf, fid, buflen - OVL_FH_WIRE_OFFSET);
> return fh;
> }
>
> diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
> index 87759165d32b..a0e450313ea4 100644
> --- a/fs/overlayfs/overlayfs.h
> +++ b/fs/overlayfs/overlayfs.h
> @@ -108,7 +108,7 @@ struct ovl_fh {
> u8 padding[3]; /* make sure fb.fid is 32bit aligned */
> union {
> struct ovl_fb fb;
> - u8 buf[0];
> + DECLARE_FLEX_ARRAY(u8, buf);
> };
> } __packed;
>
> --
> 2.34.1
>

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