Bug 7065

Never going to happen.

test environment: 2.6.27.7 kernel+headers, glibc 2.8, GCC 4.3.3 20081121 
(prerelease), binutils 2.19.

config flags (my standard set for this machine):

/usr/packages/glibc/2.9/configure --prefix=/usr --enable-shared \
    --enable-profile --disable-bounded --enable-bind-now        \
    --enable-add-ons=nptl,libidn --enable-kernel=2.6.25         \
    --enable-check-abi=warn --enable-omitfp                     \
    --enable-stackguard-randomization TIMEOUTFACTOR=5

Below, PASS means 'baseline test failures only'. (I also compared
configure output to verify that -fstack-protector addition did not
change the results of any configure tests, and verified that the
appropriate -fstack-protector actually appeared in gcc commandlines at
the appropriate times.)

baseline:                              PASS, by definition
patch applied, no flags specified:     PASS
-fstack-protector in CFLAGS:           PASS
-fstack-protector-all in CFLAGS:       one failure due to #7066, buffer overrun
--without-stack-protector:             PASS
--with-stack-protector:                PASS
--with-stack-protector=all:            one failure due to #7066, buffer overrun

Test failures for baseline (unpatched):

math/test-ildoubl.out:

testing long double (inline functions)
Failure: Test: expm1 (1) == M_El - 1.0
Result:
 is:          1.71828182845904523532e+00   0xd.bf0a8b14576953500000p-3
 should be:   1.71828182845904523543e+00   0xd.bf0a8b14576953600000p-3
 difference:  1.08420217248550443401e-19   0x8.00000000000000000000p-66
 ulp       :  1.0000
 max.ulp   :  0.0000
Maximal error of `expm1'
 is      : 1 ulp
 accepted: 0 ulp

Test suite completed:
  3618 test cases plus 3005 tests for exception flags executed.
  2 errors occurred.

elf/check-localplt.out:

--- ../scripts/data/localplt-i386-linux-gnu.data        2006-01-11 
21:06:19.000000000 +0000
+++ -   2008-11-30 20:52:09.962033876 +0000
@@ -1,4 +1,5 @@
 libc.so: _Unwind_Find_FDE
+libc.so: __bzero
 libc.so: calloc
 libc.so: free
 libc.so: malloc

(This looks like something missing from localplt-i386-linux-gnu.data to
me, not a bug.)

(Holes in test coverage: not tested with a GCC too old to support
-fstack-protector. Static testing not performed: see #7064.)

Created attachment 3087 [details]
stack protector support for glibc

This is posted at the request of Carlos O'Donell. TBH I don't care if it
doesn't go upstream, although given that it's already found a buffer overrun in
glibc I'd find that surprising. I'm more interested in distros picking it up.

(And 'never going to happen' is a peculiar statement. It has 'happened'. The
patch *exists*.)

Nix

A failure in elf/check-localplt.out as indicated by a new symbol in
scripts/data/localplt-i386-linux-gnu.data means that libc proper is invoking the
new symbol via the plt when in-fact it should be making a direct invocation to a
libc internal symbol.  There are very few conditions under which this is allowed
(notably those cases where we allow libc functionality to be overridden).

I've looked through the code and it appears that the sunrpc code is the only
relevant code which uses __bzero.  I don't think there's an internal hidden
version of the symbol.  So these calls to __bzero probably shouldn't be there. 
Instead, they should use memset.  Or perhaps that patch which you're using uses
__bzero?

In order to verify, one can look at the symbol table:

objdump -DR libc.so > libc.dis

Search libc.dis for:

__bzero@plt

You should see a plt call stub, e.g.

00016198 <__bzero@plt>:
   16198:       ff a3 0c 00 00 00       jmp    *0xc(%ebx)
   1619e:       68 00 00 00 00          push   $0x0
   161a3:       e9 e0 ff ff ff          jmp    16188 <h_errno+0x16168>

Now search for: "call   16198"

call   16198 <__bzero@plt>

This should bring you to the disassembly of the function which invoked __bzero
via the PLT.  You can then go into the C source file and replace this with a
memset.  Do this for all calls to the address for __bzero.

Here's a more thorough write-up of the same thing I just posted:

http://sources.redhat.com/glibc/wiki/Testing/Check-localplt

Invocation of __bzero() by the sunrpc code is acceptable since that code is in a
different library than libc.so so access via the PLT is expected.

Nice description, Ryan :)

A lot of the sunrpc code *does* land in libc (all the client code). Notably, 
bindresvport(), clnt_create(), clnt_broadcast(), universal() (called from 
registerrpc() via a callback from svc_register()), svctcp_create(), 
svcudp_bufcreate(), and key_gendes(), _des_crypt() (obviously used for 
DES-encrypted SunRPC), all explicitly call __bzero() and land in libc.

Almost certainly these would use memset() were the SunRPC code not ancient 
Sun-derived gunge with a 1986 copyright date...

Keep it going, guys.

To Ulrich Drepper:
How do you mean: "Never going to happen."?!

I always keen on people ignoring security measures.

Regards,
Dw.

I've been using a compromise. Glibc's programs can be compiled 
with -fstack-protector-all, or whatever other options you may want 
(-D_FORTIFY_SOURCE=2, -fPIE, etc), but not the libraries. I use the configparms 
file and set build-programs=no to build the libraries 
without -fstack-protector, then remove build-programs=no and add 'CFLAGS 
+= -fstack-protector-all' to configparms. No patches needed, test suites pass 
(remove -fstack-protector during the test suite), no crashes.

Created attachment 6248 [details]
stack protector support against eglibc 2.13.

This is the most recent version of this patch, against eglibc 2.13 (because
that happens to be the version I'm using now, as I track Debian's glibc). It
has needed no significant revisions for years, though the recent csu changes in
upstream glibc may necessitate some small revisions.

(The ChangeLog is out of date: I haven't regenerated it since 2008.)

Your change contains two different changes:
* Supporting stack-protector
* A different implementation of chk_fail function

For addition to glibc, I would only look at the stack-protector support. I
suggest you continue discussing this on the libc-alpha list.