upgrading libc6 to 2.11.1-0ubuntu7.14 breaks libmysqlclient, which in turn breaks almost everything on a web server (both amd64 and i386, I had two production servers hit by this):
*** glibc detected *** mysql: munmap_chunk(): invalid pointer: 0x00007f5f0f9da3f2 ***
======= Backtrace: =========
/lib/libc.so.6(+0x78cc6)[0x7f5f0dc24cc6]
/lib/libc.so.6(+0x125ec9)[0x7f5f0dcd1ec9]
/lib/libc.so.6(+0x12628b)[0x7f5f0dcd228b]
/lib/libc.so.6(getservbyname_r+0x183)[0x7f5f0dcb4de3]
/lib/libc.so.6(getservbyname+0x7b)[0x7f5f0dcb4b5b]
/usr/lib/libmysqlclient.so.16(mysql_server_init+0x91)[0x7f5f0eda16e1]
mysql(main+0x2cf)[0x7f5f0fa3854f]
/lib/libc.so.6(__libc_start_main+0xfd)[0x7f5f0dbcacad]
mysql(+0xf7a9)[0x7f5f0fa2f7a9]
======= Memory map: ========
7f5f0d9a8000-7f5f0d9aa000 r-xp 00000000 fb:00 14617 /lib/libdl-2.11.1.so
7f5f0d9aa000-7f5f0dbaa000 ---p 00002000 fb:00 14617 /lib/libdl-2.11.1.so
7f5f0dbaa000-7f5f0dbab000 r--p 00002000 fb:00 14617 /lib/libdl-2.11.1.so
7f5f0dbab000-7f5f0dbac000 rw-p 00003000 fb:00 14617 /lib/libdl-2.11.1.so
7f5f0dbac000-7f5f0dd2b000 r-xp 00000000 fb:00 14625 /lib/libc-2.11.1.so
7f5f0dd2b000-7f5f0df2b000 ---p 0017f000 fb:00 14625 /lib/libc-2.11.1.so
7f5f0df2b000-7f5f0df2f000 r--p 0017f000 fb:00 14625 /lib/libc-2.11.1.so
7f5f0df2f000-7f5f0df30000 rw-p 00183000 fb:00 14625 /lib/libc-2.11.1.so
7f5f0df30000-7f5f0df35000 rw-p 00000000 00:00 0
7f5f0df35000-7f5f0df4b000 r-xp 00000000 fb:00 3374 /lib/libgcc_s.so.1
7f5f0df4b000-7f5f0e14a000 ---p 00016000 fb:00 3374 /lib/libgcc_s.so.1
7f5f0e14a000-7f5f0e14b000 r--p 00015000 fb:00 3374 /lib/libgcc_s.so.1
7f5f0e14b000-7f5f0e14c000 rw-p 00016000 fb:00 3374 /lib/libgcc_s.so.1
7f5f0e14c000-7f5f0e1ce000 r-xp 00000000 fb:00 14619 /lib/libm-2.11.1.so
7f5f0e1ce000-7f5f0e3cd000 ---p 00082000 fb:00 14619 /lib/libm-2.11.1.so
7f5f0e3cd000-7f5f0e3ce000 r--p 00081000 fb:00 14619 /lib/libm-2.11.1.so
7f5f0e3ce000-7f5f0e3cf000 rw-p 00082000 fb:00 14619 /lib/libm-2.11.1.so
7f5f0e3cf000-7f5f0e4c5000 r-xp 00000000 fb:00 4849 /usr/lib/libstdc++.so.6.0.13
7f5f0e4c5000-7f5f0e6c5000 ---p 000f6000 fb:00 4849 /usr/lib/libstdc++.so.6.0.13
7f5f0e6c5000-7f5f0e6cc000 r--p 000f6000 fb:00 4849 /usr/lib/libstdc++.so.6.0.13
7f5f0e6cc000-7f5f0e6ce000 rw-p 000fd000 fb:00 4849 /usr/lib/libstdc++.so.6.0.13
7f5f0e6ce000-7f5f0e6e3000 rw-p 00000000 00:00 0
7f5f0e6e3000-7f5f0e6f9000 r-xp 00000000 fb:00 3567 /lib/libz.so.1.2.3.3
7f5f0e6f9000-7f5f0e8f8000 ---p 00016000 fb:00 3567 /lib/libz.so.1.2.3.3
7f5f0e8f8000-7f5f0e8f9000 r--p 00015000 fb:00 3567 /lib/libz.so.1.2.3.3
7f5f0e8f9000-7f5f0e8fa000 rw-p 00016000 fb:00 3567 /lib/libz.so.1.2.3.3
7f5f0e8fa000-7f5f0e911000 r-xp 00000000 fb:00 14606 /lib/libnsl-2.11.1.so
7f5f0e911000-7f5f0eb10000 ---p 00017000 fb:00 14606 /lib/libnsl-2.11.1.so
7f5f0eb10000-7f5f0eb11000 r--p 00016000 fb:00 14606 /lib/libnsl-2.11.1.so
7f5f0eb11000-7f5f0eb12000 rw-p 00017000 fb:00 14606 /lib/libnsl-2.11.1.so
7f5f0eb12000-7f5f0eb14000 rw-p 00000000 00:00 0
7f5f0eb14000-7f5f0eb1d000 r-xp 00000000 fb:00 14611 /lib/libcrypt-2.11.1.so
7f5f0eb1d000-7f5f0ed1d000 ---p 00009000 fb:00 14611 /lib/libcrypt-2.11.1.so
7f5f0ed1d000-7f5f0ed1e000 r--p 00009000 fb:00 14611 /lib/libcrypt-2.11.1.so
7f5f0ed1e000-7f5f0ed1f000 rw-p 0000a000 fb:00 14611 /lib/libcrypt-2.11.1.so
7f5f0ed1f000-7f5f0ed4d000 rw-p 00000000 00:00 0
7f5f0ed4d000-7f5f0ef0c000 r-xp 00000000 fb:00 4810 /usr/lib/libmysqlclient.so.16.0.0
7f5f0ef0c000-7f5f0f10c000 ---p 001bf000 fb:00 4810 /usr/lib/libmysqlclient.so.16.0.0
7f5f0f10c000-7f5f0f111000 r--p 001bf000 fb:00 4810 /usr/lib/libmysqlclient.so.16.0.0
7f5f0f111000-7f5f0f15b000 rw-p 001c4000 fb:00 4810 /usr/lib/libmysqlclient.so.16.0.0
7f5f0f15b000-7f5f0f15d000 rw-p 00000000 00:00 0
7f5f0f15d000-7f5f0f175000 r-xp 00000000 fb:00 14615 /lib/libpthread-2.11.1.so
7f5f0f175000-7f5f0f374000 ---p 00018000 fb:00 14615 /lib/libpthread-2.11.1.so
7f5f0f374000-7f5f0f375000 r--p 00017000 fb:00 14615 /lib/libpthread-2.11.1.so
7f5f0f375000-7f5f0f376000 rw-p 00018000 fb:00 14615 /lib/libpthread-2.11.1.so
7f5f0f376000-7f5f0f37a000 rw-p 00000000 00:00 0
7f5f0f37a000-7f5f0f3b8000 r-xp 00000000 fb:00 3377 /lib/libncurses.so.5.7
7f5f0f3b8000-7f5f0f5b8000 ---p 0003e000 fb:00 3377 /lib/libncurses.so.5.7
7f5f0f5b8000-7f5f0f5bc000 r--p 0003e000 fb:00 3377 /lib/libncurses.so.5.7
7f5f0f5bc000-7f5f0f5bd000 rw-p 00042000 fb:00 3377 /lib/libncurses.so.5.7
7f5f0f5bd000-7f5f0f5f6000 r-xp 00000000 fb:00 2838 /lib/libreadline.so.6.1
7f5f0f5f6000-7f5f0f7f5000 ---p 00039000 fb:00 2838 /lib/libreadline.so.6.1
7f5f0f7f5000-7f5f0f7f7000 r--p 00038000 fb:00 2838 /lib/libreadline.so.6.1
7f5f0f7f7000-7f5f0f7fd000 rw-p 0003a000 fb:00 2838 /lib/libreadline.so.6.1
7f5f0f7fd000-7f5f0f7fe000 rw-p 00000000 00:00 0
7f5f0f7fe000-7f5f0f81e000 r-xp 00000000 fb:00 14610 /lib/ld-2.11.1.so
7f5f0f9da000-7f5f0fa0f000 r--s 00000000 fb:00 137807 /var/cache/nscd/services
7f5f0fa0f000-7f5f0fa16000 rw-p 00000000 00:00 0
7f5f0fa1b000-7f5f0fa1d000 rw-p 00000000 00:00 0
7f5f0fa1d000-7f5f0fa1e000 r--p 0001f000 fb:00 14610 /lib/ld-2.11.1.so
7f5f0fa1e000-7f5f0fa1f000 rw-p 00020000 fb:00 14610 /lib/ld-2.11.1.so
7f5f0fa1f000-7f5f0fa20000 rw-p 00000000 00:00 0
7f5f0fa20000-7f5f0fa43000 r-xp 00000000 fb:00 9356 /usr/bin/mysql
7f5f0fc43000-7f5f0fc44000 r--p 00023000 fb:00 9356 /usr/bin/mysql
7f5f0fc44000-7f5f0fc4e000 rw-p 00024000 fb:00 9356 /usr/bin/mysql
7f5f0fc4e000-7f5f0fc4f000 rw-p 00000000 00:00 0
7f5f10bbd000-7f5f10bde000 rw-p 00000000 00:00 0 [heap]
7fff0de06000-7fff0de1b000 rw-p 00000000 00:00 0 [stack]Aborted
Workaround: downgrade manually to 2.11.1-0ubuntu7.13 (doesn't work with "apt-get install libc6==2.11.1-0ubuntu7.13", for some reason):
dpkg -i /var/cache/apt/archives/libc-bin_2.11.1-0ubuntu7.13_amd64.deb &&
dpkg -i /var/cache/apt/archives/libc6_2.11.1-0ubuntu7.13_amd64.deb
Status changed to 'Confirmed' because the bug affects multiple users.