Re: libsemanage/libsepol still supported for non-MLS/MCS setups?

[Stephen Smalley <sds@tycho.nsa.gov>]

On Thu, 2012-02-23 at 21:17 +0100, Sven Vermeulen wrote:
> Hi guys,
> 
> Is libsemanage (and libsepol) still supported on policies without MLS/MCS?
> For some reason, I get segfaults when using libsemanage-2.1.6 on a "strict"
> policy (one without levels).
> 
> The backtrace is as follows:
> 
> (gdb) run -B
> Starting program: /usr/sbin/semodule -B
> 
> Program received signal SIGSEGV, Segmentation fault.
> __strlen_sse2 () at ../sysdeps/x86_64/multiarch/../strlen.S:32
> 32      ../sysdeps/x86_64/multiarch/../strlen.S: No such file or directory.
>         in ../sysdeps/x86_64/multiarch/../strlen.S
> (gdb) bt
> #0  __strlen_sse2 () at ../sysdeps/x86_64/multiarch/../strlen.S:32
> #1  0x000003a1d08ddce1 in ustr_replace_cstr () from /usr/lib64/libustr-1.0.so.1
> #2  0x000003a1d1524835 in replace_all (str=0x3a1d88e93c0 "HOME_DIR/.+\tsystem_u:object_r:user_home_t", repl=0x3ffffffde00)
>     at genhomedircon.c:499
> #3  0x000003a1d1524b58 in write_home_dir_context (s=0x3ffffffdf20, out=0x3a1d7444510, tpl=0x3a1d6e1f1b0, 
>     user=0x3a1d71b2680 "user_u", seuser=0x3a1d71b2680 "user_u", home=0x3a1d71e08a3 "/home/[^/]*", 
>     role_prefix=0x3a1d71bafc0 "user", level=0x0) at genhomedircon.c:566
> #4  0x000003a1d1525d68 in write_context_file (s=0x3ffffffdf20, out=0x3a1d7444510) at genhomedircon.c:998
> #5  0x000003a1d1526054 in semanage_genhomedircon (sh=0x3a1d1b6b280, policydb=0x3a1d6e01dd0, usepasswd=1, ignoredirs=0x0)
>     at genhomedircon.c:1076
> #6  0x000003a1d151e30c in semanage_direct_commit (sh=0x3a1d1b6b280) at direct_api.c:994
> #7  0x000003a1d15234fe in semanage_commit (sh=0x3a1d1b6b280) at handle.c:435
> #8  0x000003a1d1969318 in main (argc=<optimized out>, argv=0x3ffffffe278) at semodule.c:466
> 
> As you can see in frame #3, level is 0x0, which is confirmed when
> traversing the &s variable in the write_context_file function:
> 
> (gdb) frame 4
> #4  0x000003a1d1525d68 in write_context_file (s=0x3ffffffdf20, out=0x3a1d7444510) at genhomedircon.c:998
> 998     genhomedircon.c: No such file or directory.
>         in genhomedircon.c
> (gdb) print s.fallback_user_level
> $1 = 0x0
> (gdb) print s.fallback_user      
> $2 = 0x3a1d71b2680 "user_u"
> (gdb) print s.fallback_user_prefix
> $3 = 0x3a1d71bafc0 "user"
> 
> Looking at how this can become 0x0, I think that 
> 
> 1. write_context_file calls setup_fallback_user
> 2. setup_fallback_user calls semanage_user_query (for a default account?)
>    this returns >= 0
> 3. setup_fallback_user calls semanage_user_get_mlslevel
> 4. semanage_user_get_mlslevel eventually calls sepol_user_get_mlslevel
> 5. sepol_user_get_mlslevel returns 0x0
> 
> Should sepol_user_get_mlslevel return some default (like "s0") if the
> system doesn't use MLS/MCS? Or shouldn't it be called if one doesn't have
> MCS/MLS?

Looks the same to me as:
http://marc.info/?t=131443240600002&r=1&w=2
http://marc.info/?t=132433045500005&r=1&w=2

It seems that last patch never got applied.

The non-MCS/MLS case doesn't get much testing since most of the
distributions seem to enable MCS in their default policies.

-- 
Stephen Smalley
National Security Agency


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