[Bug 1571456] [NEW] id crashed with SIGSEGV in sock_eq()

[Launchpad Bug Tracker]

You have been subscribed to a public bug by Anders Kaseorg (anders-kaseorg):

[Impact]

The nss_hesiod nsswitch module, which worked in previous releases, does
not work at all in Ubuntu 16.04.  Enabling it causes NULL pointer
dereferences in calls such as getpwuid().

[Test Case]

# sed -i 's/passwd: *compat/& hesiod/' /etc/nsswitch.conf
# cat > /etc/hesiod.conf <<EOF
lhs=.ns
rhs=.athena.mit.edu
EOF
# id andersk
Segmentation fault (core dumped)

Expected output: uid=39270(andersk) gid=101(…) groups=101(…).

[Regression Potential]

I wrote a 6-line patch that conditionalizes an errant res_nclose call.
There is also a bigger upstream patch on the glibc 2.22 and 2.23 stable
branches that entirely removes the unused abstraction that necessitated
the res_nclose calls at all.  Neither patch makes any changes outside of
the glibc hesiod directory, which as of now is so thoroughly broken that
there is nothing left to regress.

[Other Info]

ProblemType: Crash
DistroRelease: Ubuntu 16.04
Package: coreutils 8.25-2ubuntu2
ProcVersionSignature: Ubuntu 4.4.0-18.34-generic 4.4.6
Uname: Linux 4.4.0-18-generic x86_64
NonfreeKernelModules: openafs
ApportVersion: 2.20.1-0ubuntu2
Architecture: amd64
CurrentDesktop: GNOME
Date: Sun Apr 17 22:39:06 2016
EcryptfsInUse: Yes
ExecutablePath: /usr/bin/id
ExecutableTimestamp: 1455802667
InstallationDate: Installed on 2016-02-19 (58 days ago)
InstallationMedia: Ubuntu-GNOME 16.04 LTS "Xenial Xerus" - Alpha amd64 (20160218)
ProcCmdline: id andersk
ProcCwd: /home/anders
SegvAnalysis:
 Segfault happened at: 0x7fef32217a88 <__libc_res_nsend+3192>:	cmp    %dx,(%rax)
 PC (0x7fef32217a88) ok
 source "%dx" ok
 destination "(%rax)" (0x00000000) not located in a known VMA region (needed writable region)!
SegvReason: writing NULL VMA
Signal: 11
SourcePackage: coreutils
StacktraceTop:
 sock_eq (a2=0x0, a1=0x7fef33b9daf4 <_res+20>) at res_send.c:1584
 __libc_res_nsend (statp=0x7fef33b9dae0 <_res>, buf=buf at entry=0x7ffd88e80910 "@\267\001", buflen=45, buf2=buf2 at entry=0x0, buflen2=buflen2 at entry=0, ans=ans at entry=0x7ffd88e80d10 " you want.  Don't add spaces after the\n", anssiz=1024, ansp=0x0, ansp2=0x0, nansp2=0x0, resplen2=0x0, ansp2_malloced=0x0) at res_send.c:408
 __GI___res_nsend (statp=<optimized out>, buf=buf at entry=0x7ffd88e80910 "@\267\001", buflen=<optimized out>, ans=ans at entry=0x7ffd88e80d10 " you want.  Don't add spaces after the\n", anssiz=anssiz at entry=1024) at res_send.c:630
 get_txt_records (class=1, name=name at entry=0xff3dd0 "39270.uid.ns.athena.mit.edu", ctx=0xff27e0) at hesiod.c:374
 hesiod_resolve (context=context at entry=0xff27e0, name=name at entry=0x7ffd88e81190 "39270", type=type at entry=0x7fef3242a486 "uid") at hesiod.c:240
Title: id crashed with SIGSEGV in sock_eq()
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm bumblebee cdrom dip libvirtd lpadmin plugdev sambashare sbuild sudo wireshark

** Affects: glibc
     Importance: Unknown
         Status: Unknown

** Affects: glibc (Ubuntu)
     Importance: Medium
     Assignee: Adam Conrad (adconrad)
         Status: Fix Released

** Affects: glibc (Ubuntu Xenial)
     Importance: Undecided
         Status: Confirmed

** Affects: glibc (Debian)
     Importance: Unknown
         Status: Fix Released

** Affects: glibc (Fedora)
     Importance: Unknown
         Status: Unknown


** Tags: amd64 apport-crash patch regression-release xenial
-- 
id crashed with SIGSEGV in sock_eq()
https://bugs.launchpad.net/bugs/1571456
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