Bug#23010 _my_b_read() passing illegal file handles to my_seek()

- The io cache flag seek_not_done was not set properly in the 
  reinit_io_cache function call and this led my_seek to be called
  desipite an invalid file handle.
- Added a test in reinit_io_cache to ensure we have a valid file 
  handle before setting seek_not_done flag.


mysys/mf_iocache.c:
  Added a test to only trigger my_seek function calls if we have
  a valid file descriptor.
mysys/my_seek.c:
  Refactored incomplete condition into an assertion. This also ensures
  that variable newpos is initialized properly.

1 files changed, 5 insertions, 1 deletions

diff --git a/mysys/mf_iocache.c b/mysys/mf_iocache.c
index a7937da0cc2..5f0069d9bed 100644
--- a/mysys/mf_iocache.c
+++ b/mysys/mf_iocache.c
@@ -313,7 +313,11 @@ my_bool reinit_io_cache(IO_CACHE *info, enum cache_type type,
       if (info->type == READ_CACHE)
       {
 	info->write_end=info->write_buffer+info->buffer_length;
-	info->seek_not_done=1;
+        /*
+          Trigger a new seek only if we have a valid
+          file handle.
+        */
+        info->seek_not_done= (info->file >= 0);
       }
       info->end_of_file = ~(my_off_t) 0;
     }