[PATCH 1/4] libsframe: fix checks in flip_fde

[Jens Remus]

Hello Indu!

On 11/3/2025 8:52 PM, Indu Bhagat wrote:
> Adjust the check for optional trailing section padding to account for
> the case of ihp->sfh_fdeoff != 0 or ihp->sfh_freoff != total FDEs size.

When would ihp->sfh_fdeoff != 0 occur?  If there is an auxiliary header?
In SFrame V3?

If ihp->sfh_fdeoff != 0, wouldn't then ihp->sfh_freoff != total FDEs size,
because I would naively assume (ihp->sfh_freoff - ihp->sfh_fdeoff) == total FDEs size.

> 
> libsframe/
>         * sframe.c (flip_sframe): Fix checks in flip_fde to accommodate
> 	cases when sfh_fdeoff != 0 or when SFrame FREs are placed after
> 	a gap from SFrame FDEs.
> ---
>  libsframe/sframe.c | 20 ++++++++++++++------
>  1 file changed, 14 insertions(+), 6 deletions(-)
> 
> diff --git a/libsframe/sframe.c b/libsframe/sframe.c
> index dfff1b3490a..e2d987f5822 100644
> --- a/libsframe/sframe.c
> +++ b/libsframe/sframe.c
> @@ -603,7 +603,8 @@ flip_sframe (char *frame_buf, size_t buf_size, uint32_t to_foreign)
>    size_t hdrsz = 0;
>    int err = 0;
>    /* For error checking.  */
> -  size_t bytes_flipped = 0;
> +  size_t fde_bytes_flipped = 0;
> +  size_t fre_bytes_flipped = 0;
>  
>    /* Header must be in host endianness at this time.  */
>    ihp = (sframe_header *)frame_buf;
> @@ -635,7 +636,7 @@ flip_sframe (char *frame_buf, size_t buf_size, uint32_t to_foreign)
>        if (flip_fde (fdes, buf_end - fdes, ver, &fsz))
>  	goto bad;
>  
> -      bytes_flipped += fsz;
> +      fde_bytes_flipped += fsz;
>  
>        if (!to_foreign && sframe_decode_fde (fdes, fdes - buf_end, ver,
>  					    &num_fres, &fre_type, &fre_offset,
> @@ -647,7 +648,7 @@ flip_sframe (char *frame_buf, size_t buf_size, uint32_t to_foreign)
>  	{
>  	  if (flip_fre (fp, fre_type, &esz))
>  	    goto bad;
> -	  bytes_flipped += esz;
> +	  fre_bytes_flipped += esz;
>  
>  	  if (esz == 0 || esz > buf_size)
>  	    goto bad;
> @@ -655,11 +656,18 @@ flip_sframe (char *frame_buf, size_t buf_size, uint32_t to_foreign)
>  	}
>        prev_frep_index = j;
>      }
> -  /* All FDEs and FREs must have been endian flipped by now.  */
> -  if ((j != ihp->sfh_num_fres) || (bytes_flipped > (buf_size - hdrsz)))
> +
> +  /* All FDEs must have been endian flipped by now.  */
> +  if (i != num_fdes || fde_bytes_flipped > ihp->sfh_freoff)

Doesn't ihp->sfh_fdeoff need to be subtracted from ihp->sfh_freoff to
determine the total FDEs size?

  if (i != num_fdes || fde_bytes_flipped > ihp->sfh_freoff - ihp->sfh_fdeoff)

> +    goto bad;
> +
> +  /* All FREs must have been endian flipped by now.  */
> +  if (j != ihp->sfh_num_fres || fre_bytes_flipped > ihp->sfh_fre_len)
>      goto bad;
> +
>    /* Optional trailing section padding.  */
> -  for (fp = frame_buf + hdrsz + bytes_flipped; fp < frame_buf + buf_size; fp++)
> +  size_t frame_size = hdrsz + ihp->sfh_freoff + fre_bytes_flipped;
> +  for (fp = frame_buf + frame_size; fp < frame_buf + buf_size; fp++)
>      if (*fp != '\0')
>        goto bad;
>  

Thanks and regards,
Jens
-- 
Jens Remus
Linux on Z Development (D3303)
+49-7031-16-1128 Office
jremus@de.ibm.com

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