libsepol: check decl_id bounds before using it

When loading an invalid module which uses a declaration ID 0,
semodule_package crashes in policydb_index_decls():

    p->decl_val_to_struct[decl->decl_id - 1] = decl;

gdb shows the following stack trace:

    #0  0x00007ffff7aa1bbd in policydb_index_decls (p=p@entry=0x605360)
    at policydb.c:1034
    #1  0x00007ffff7aaa9fc in policydb_read (p=<optimized out>,
    fp=fp@entry=0x605090, verbose=verbose@entry=0) at policydb.c:3958
    #2  0x00007ffff7ab4764 in sepol_policydb_read (p=<optimized out>,
    pf=pf@entry=0x605090) at policydb_public.c:174
    #3  0x0000000000401d33 in main (argc=<optimized out>,
    argv=0x7fffffffdc88) at semodule_package.c:220

Change policydb_index_decls() to report an error instead:

    libsepol.policydb_index_decls: invalid decl ID 0

Signed-off-by: Nicolas Iooss <nicolas.iooss@m4x.org>
1 file changed