error checking: check for avail_block consistency before using it

* src/gdbmdefs.h (gdbm_avail_block_valid_p): New function.
* src/gdbm.h.in (GDBM_BAD_AVAIL): New error code.
* src/gdbmerrno.c: Support new error code.
* src/falloc.c (pop_avail_block): Validate the avail_block
* src/gdbmopen.c (validate_header): Validate the avail_block.
* src/gdbmtool.c (_gdbm_avail_list_size)
(_gdbm_print_avail_list): Validate the avail_block.

1 files changed, 7 insertions, 0 deletions

diff --git a/src/gdbmdefs.h b/src/gdbmdefs.h
index bd104e2..5305b0d 100644
--- a/src/gdbmdefs.h
+++ b/src/gdbmdefs.h
@@ -51,6 +51,13 @@ typedef struct
   avail_elem av_table[1]; /* The table.  Make it look like an array.  */
 } avail_block;
 
+/* Return true if avail_block is valid */
+static int inline
+gdbm_avail_block_valid_p (avail_block const *av)
+{
+  return (av->size >= 0 && av->count >= 0 && av->count <= av->size);
+}
+
 /* The dbm file header keeps track of the current location of the hash
    directory and the free space in the file.  */