lbgdbm3 segfaults

here's the tarball.

To be clear, my test program works on 32 bit x86 debian jessie. however it does not work with 64 bit trisquel belenos. i have not tested 32 bit trisquel or 64 bit jessie.

here is a backtrace on the trisquel box:

(gdb) run
Starting program: /srv/data/home/s/sudoman/etc/gdbm-test/gdbm-test

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7bd6a99 in _gdbm_get_bucket () from /usr/lib/x86_64-linux-gnu/libgdbm.so.3
(gdb) backtrace
#0 0x00007ffff7bd6a99 in _gdbm_get_bucket () from /usr/lib/x86_64-linux-gnu/libgdbm.so.3
#1 0x00007ffff7bd6824 in gdbm_firstkey () from /usr/lib/x86_64-linux-gnu/libgdbm.so.3
#2 0x0000000000400854 in main ()

i tested the 32 bit trisquel 7.0 live cd and the program did not segfault.

i got a segfault on 64 bit debian jessie. i even tried building the .deb from source, but still got the segfault.

this appears to be an issue with 64 bit binaries of this library.

the bug occurs in the gdbm_open() function on the 64 bit system i have tested.

it appears that gdbm is performing a read of the database file at the end of the function in gdbmopen.c. it receives 0 bytes.

according to the read() manpage, zero bytes are returned when the end of the file has been reached.

--- 32.txt 2015-12-14 23:43:53.019407733 -0500
+++ 64.txt 2015-12-14 23:44:00.363542380 -0500
@@ -46,14 +46,8 @@
369 if (file_pos != dbf->header->dir)
376 num_bytes = read (dbf->desc, dbf->dir, dbf->header->dir_size);
377 if (num_bytes != dbf->header->dir_size)
-387 dbf->last_read = -1;
-388 dbf->bucket = NULL;
-389 dbf->bucket_dir = 0;
-390 dbf->cache_entry = NULL;
-391 dbf->header_changed = FALSE;
-392 dbf->directory_changed = FALSE;
-393 dbf->bucket_changed = FALSE;
-394 dbf->second_changed = FALSE;
-398 return dbf;
+379 gdbm_close (dbf);
+380 gdbm_errno = GDBM_FILE_READ_ERROR;
+381 return NULL;
400 }