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MDEV-40176: field_charset()->charpos(blob..) called with NULL #5304

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MDEV-40176: field_charset()->charpos(blob..) called with NULL #5304

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11 changes: 7 additions & 4 deletions sql/field.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -9035,10 +9035,13 @@ uint Field_blob::get_key_image_itRAW(const uchar *ptr_arg, uchar *buff,
{
size_t blob_length= get_length(ptr_arg);
const uchar *blob= get_ptr(ptr_arg);
size_t local_char_length= length / mbmaxlen();
local_char_length= field_charset()->charpos(blob, blob + blob_length,
local_char_length);
set_if_smaller(blob_length, local_char_length);
if (blob)

@raghunandanbhat raghunandanbhat Jun 30, 2026

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I believe this is not the only place where we call charpos function and if we were to do this kind of checks, we should be doing it in all other places too.
Fixing the root cause, i.e my_charpos_* set of functions to handle null seems like correct fix to me. thoughts @grooverdan ?

{
size_t local_char_length= length / mbmaxlen();
local_char_length= field_charset()->charpos(blob, blob + blob_length,
local_char_length);
set_if_smaller(blob_length, local_char_length);
}
Comment on lines +9038 to +9044

@gemini-code-assist gemini-code-assist Bot Jun 30, 2026

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medium

Instead of checking if (blob), it is more efficient and robust to check if (blob_length > 0). If the BLOB length is 0, there is no need to perform any character position calculations or division, as blob_length is already 0 and cannot be reduced further. This avoids redundant overhead for empty BLOBs and safely prevents passing NULL pointers to charpos.

  if (blob_length > 0)
  {
    size_t local_char_length= length / mbmaxlen();
    local_char_length= field_charset()->charpos(blob, blob + blob_length,
                                                local_char_length);
    set_if_smaller(blob_length, local_char_length);
  }

@grooverdan grooverdan Jun 30, 2026

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bit clearer. Could DBUG_ASSERT(blob) in the block too.


if (length > blob_length)
{
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