[PATCH 07/10] libsframe: guard against buffer over-read in sframe_fde_tbl_init

In SFrame V3, the FDE attribute data is stored near the SFrame FREs.  In
sframe_fde_tbl_init(), for SFrame V3 format,
fdep->sfdi_func_start_fre_off was used to index into fre_buf without
verifying if sfdi_func_start_fre_off + sizeof(sframe_func_desc_attr_v3)
<= fre_buf_len.  If left unchecked, this may cause buffer over-reads in case
of invalid SFrame data.

Pass FRE buffer len to sframe_fde_tbl_init(), and validate
sfdi_func_start_fre_off against that guard before reading FDE attribute
data.
---
 libsframe/sframe.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/libsframe/sframe.c b/libsframe/sframe.c
index 288d7c0d873..f047342a782 100644
--- a/libsframe/sframe.c
+++ b/libsframe/sframe.c
@@ -140,8 +140,8 @@ sframe_fde_tbl_alloc (sf_fde_tbl **fde_tbl, unsigned int num_fdes)
 
 static int
 sframe_fde_tbl_init (sf_fde_tbl *fde_tbl, const char *fde_buf,
-		     const char *fre_buf, size_t *fidx_size,
-		     unsigned int num_fdes, uint8_t ver)
+		     const char *fre_buf, size_t fre_buf_len,
+		     size_t *fidx_size, unsigned int num_fdes, uint8_t ver)
 {
   if (ver == SFRAME_VERSION_3 && SFRAME_VERSION == SFRAME_VERSION_3)
     {
@@ -155,6 +155,10 @@ sframe_fde_tbl_init (sf_fde_tbl *fde_tbl, const char *fde_buf,
 	  fde_tbl->entry[i].func_start_fre_off = fdep->sfdi_func_start_fre_off;
 	  /* V3 organizes the following data closer to the SFrame FREs for the
 	     function.  Access them via the sfde_func_start_fre_off.  */
+	  if (fdep->sfdi_func_start_fre_off > fre_buf_len
+	      || (sizeof (sframe_func_desc_attr_v3)
+		  > (fre_buf_len - fdep->sfdi_func_start_fre_off)))
+	    return SFRAME_ERR;
 	  const sframe_func_desc_attr_v3 *fattr
 	    = (sframe_func_desc_attr_v3 *)(fre_buf
 					   + fdep->sfdi_func_start_fre_off);
@@ -1535,7 +1539,7 @@ sframe_decode (const char *sf_buf, size_t sf_size, int *errp)
 
   /* SFrame FDEs are at an offset of sfh_fdeoff from SFrame header end.  */
   if (sframe_fde_tbl_init (dctx->sfd_funcdesc, frame_buf + dhp->sfh_fdeoff,
-			   frame_buf + dhp->sfh_freoff,
+			   frame_buf + dhp->sfh_freoff, dhp->sfh_fre_len,
 			   &fidx_size, dhp->sfh_num_fdes, sfp->sfp_version))
     {
       sframe_ret_set_errno (errp, SFRAME_ERR_BUF_INVAL);
-- 
2.43.0