bug#24138: SIGSEGV of useradd (from shadow package)

[Tomáš Čech]

It seems to be easy to crash useradd (from shadow package).

# ls -l $(which useradd)
lrwxrwxrwx 4 root guixbuild 69 Jan  1  1970 /root/.guix-profile/sbin/useradd -> 
/gnu/store/ylnc73apl1irl0s613rxjl445x2zx8a5-shadow-4.2.1/sbin/useradd


# useradd test
Neoprávněný přístup do paměti (SIGSEGV) (core dumped [obraz paměti uložen])

(139) # gdb $(which useradd) core
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Reading symbols from /root/.guix-profile/sbin/useradd...(no debugging symbols 
found)...done.
[New LWP 1603]

warning: Could not load shared library symbols for linux-vdso.so.1.
Do you need "set solib-search-path" or "set sysroot"?
Core was generated by `useradd test'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x00007f457ee6503c in call_init.part () from 
/gnu/store/8m00x5x8ykmar27s9248cmhnkdb2n54a-glibc-2.22/lib/ld-linux-x86-64.so.2
(gdb) bt
#0  0x00007f457ee6503c in call_init.part () from 
/gnu/store/8m00x5x8ykmar27s9248cmhnkdb2n54a-glibc-2.22/lib/ld-linux-x86-64.so.2
#1  0x00007f457ee65205 in _dl_init () from 
/gnu/store/8m00x5x8ykmar27s9248cmhnkdb2n54a-glibc-2.22/lib/ld-linux-x86-64.so.2
#2  0x00007f457ee696a0 in dl_open_worker () from 
/gnu/store/8m00x5x8ykmar27s9248cmhnkdb2n54a-glibc-2.22/lib/ld-linux-x86-64.so.2
#3  0x00007f457ee64f34 in _dl_catch_error () from 
/gnu/store/8m00x5x8ykmar27s9248cmhnkdb2n54a-glibc-2.22/lib/ld-linux-x86-64.so.2
#4  0x00007f457ee68d33 in _dl_open () from 
/gnu/store/8m00x5x8ykmar27s9248cmhnkdb2n54a-glibc-2.22/lib/ld-linux-x86-64.so.2
#5  0x00007f457e841fb9 in dlopen_doit () from 
/gnu/store/8m00x5x8ykmar27s9248cmhnkdb2n54a-glibc-2.22/lib/libdl.so.2
#6  0x00007f457ee64f34 in _dl_catch_error () from 
/gnu/store/8m00x5x8ykmar27s9248cmhnkdb2n54a-glibc-2.22/lib/ld-linux-x86-64.so.2
#7  0x00007f457e842589 in _dlerror_run () from 
/gnu/store/8m00x5x8ykmar27s9248cmhnkdb2n54a-glibc-2.22/lib/libdl.so.2
#8  0x00007f457e842051 in dlopen@@GLIBC_2.2.5 () from 
/gnu/store/8m00x5x8ykmar27s9248cmhnkdb2n54a-glibc-2.22/lib/libdl.so.2
#9  0x00007f457ea49e8d in _pam_load_module () from 
/gnu/store/2xmwkq2ycwk89xlxnvib5wnjaacfy0rg-linux-pam-1.2.1/lib/libpam.so.0
#10 0x00007f457ea4a4f9 in _pam_add_handler () from 
/gnu/store/2xmwkq2ycwk89xlxnvib5wnjaacfy0rg-linux-pam-1.2.1/lib/libpam.so.0
#11 0x00007f457ea4ad90 in _pam_parse_conf_file () from 
/gnu/store/2xmwkq2ycwk89xlxnvib5wnjaacfy0rg-linux-pam-1.2.1/lib/libpam.so.0
#12 0x00007f457ea4b395 in _pam_init_handlers () from 
/gnu/store/2xmwkq2ycwk89xlxnvib5wnjaacfy0rg-linux-pam-1.2.1/lib/libpam.so.0
#13 0x00007f457ea4cae1 in pam_start () from 
/gnu/store/2xmwkq2ycwk89xlxnvib5wnjaacfy0rg-linux-pam-1.2.1/lib/libpam.so.0
#14 0x0000000000403351 in main ()


Interesting information about module causing it would be in stackframe
#9 but there are no debugging information available. Adding debug
`output' to linux-pam would diverge me from GuixSD.

from strace:

read(3, "account required pam_deny.so \nau"..., 4096) = 223
open("/gnu/store/2xmwkq2ycwk89xlxnvib5wnjaacfy0rg-linux-pam-1.2.1/lib/security/pam_deny.so",
 O_RDONLY|O_CLOEXEC) = 5
read(5, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\340\6\0\0\0\0\0\0"..., 
832) = 832
fstat(5, {st_mode=S_IFREG|0555, st_size=6728, ...}) = 0
mmap(NULL, 2100200, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 5, 0) = 
0x7fb8b447c000
mprotect(0x7fb8b447d000, 2093056, PROT_NONE) = 0
mmap(0x7fb8b467c000, 4096, PROT_READ|PROT_WRITE, 
MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 5, 0) = 0x7fb8b467c000
close(5)                                = 0
--- SIGSEGV {si_signo=SIGSEGV, si_code=SEGV_MAPERR, si_addr=0x7fb8b3d1bda8} ---
+++ killed by SIGSEGV (core dumped) +++

# cat /etc/pam.d/useradd
account required pam_unix.so
auth sufficient pam_rootok.so
password required pam_unix.so
session required 
/gnu/store/4mmn5y6syzv7wwz1y6bl1ab4g0yvkdq1-elogind-219.14/lib/security/pam_elogind.so
session required pam_unix.so

# cat /etc/pam.d/other
account required pam_deny.so
auth required pam_deny.so
password required pam_deny.so
session required 
/gnu/store/4mmn5y6syzv7wwz1y6bl1ab4g0yvkdq1-elogind-219.14/lib/security/pam_elogind.so
session required pam_deny.so

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