* [PATCH] ovl: Use "buf" flexible array for memcpy() destination
@ 2022-09-24 7:33 Kees Cook
2022-09-24 16:32 ` Gustavo A. R. Silva
0 siblings, 1 reply; 2+ messages in thread
From: Kees Cook @ 2022-09-24 7:33 UTC (permalink / raw)
To: Miklos Szeredi
Cc: Kees Cook, linux-unionfs, syzbot+9d14351a171d0d1c7955,
linux-kernel, linux-hardening
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>
---
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
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] ovl: Use "buf" flexible array for memcpy() destination
2022-09-24 7:33 [PATCH] ovl: Use "buf" flexible array for memcpy() destination Kees Cook
@ 2022-09-24 16:32 ` Gustavo A. R. Silva
0 siblings, 0 replies; 2+ messages in thread
From: Gustavo A. R. Silva @ 2022-09-24 16:32 UTC (permalink / raw)
To: Kees Cook
Cc: Miklos Szeredi, linux-unionfs, syzbot+9d14351a171d0d1c7955,
linux-kernel, linux-hardening
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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