[PATCH 02/10] libsframe: guard against malformed rep_block_size

From: Indu Bhagat <[email protected]>

When checking for an applicable FRE, guard against invalid data in
rep_block_size, lest there be an arithmetic exception caused by division
by zero.  Similar code was flagged by Sashiko in the stacktracer patches
for Linux kernel earlier.
---
 libsframe/sframe.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/libsframe/sframe.c b/libsframe/sframe.c
index 011884c0768..712dd0fdb68 100644
--- a/libsframe/sframe.c
+++ b/libsframe/sframe.c
@@ -600,7 +600,12 @@ sframe_fre_check_range_p (const sframe_decoder_ctx *dctx, uint32_t func_idx,
   /* For SFrame FDEs encoding information for repetitive pattern of insns,
      masking with the rep_block_size is necessary to find the matching FRE.  */
   if (mask_p)
-    pc_offset = pc_offset % rep_block_size;
+    {
+      /* Treat a zero-sized repeat block as malformed input.  */
+      if (rep_block_size == 0)
+	return false;
+      pc_offset = pc_offset % rep_block_size;
+    }
 
   return (start_ip_offset <= pc_offset) && (end_ip_offset >= pc_offset);
 }
-- 
2.43.0