Re: [PATCH] iproute2: Conforming to -D_FORTIFY_SOURCE=2 restrictions

[Eric Dumazet <eric.dumazet@gmail.com>]

Le mercredi 19 octobre 2011 à 17:15 +0800, Bin Li a écrit :
> Stephen,
> 
>  You can reproduce this issue in 2.6.37 like below. And the previous
> gdb log is after the install the debuginfo package in SUSE.
> 
> # ip -6 xfrm state add src 3ffe:501:ffff:ff03:21a:64ff:fe12:e4c1 dst
> 3ffe:501:ffff:ff05:200:ff:fe00:c1c1 proto ah spi 0x1000 mode transport
> auth md5 "TAHITEST89ABCDEF"
> 
> *** buffer overflow detected ***: ip terminated
> ======= Backtrace: =========
> /lib/libc.so.6(__fortify_fail+0x40)[0xb76d0070]
> /lib/libc.so.6(+0xe8e27)[0xb76cde27]
> /lib/libc.so.6(+0xe8317)[0xb76cd317]
> ip[0x806d6c4]
> ip(do_xfrm_state+0x120)[0x806dc70]
> ip(do_xfrm+0x81)[0x806ad51]
> ip[0x804c355]
> ip(main+0x476)[0x804caa6]
> /lib/libc.so.6(__libc_start_main+0xfe)[0xb75fbc2e]
> ip[0x804c261]
> ======= Memory map: ========
> 08048000-08087000 r-xp 00000000 08:01 4465       /sbin/ip
> 08087000-08088000 r--p 0003e000 08:01 4465       /sbin/ip
> 08088000-0808a000 rw-p 0003f000 08:01 4465       /sbin/ip
> 0808a000-080ad000 rw-p 00000000 00:00 0          [heap]
> b75c6000-b75e2000 r-xp 00000000 08:01 131084     /lib/libgcc_s.so.1
> b75e2000-b75e3000 r--p 0001b000 08:01 131084     /lib/libgcc_s.so.1
> b75e3000-b75e4000 rw-p 0001c000 08:01 131084     /lib/libgcc_s.so.1
> b75e4000-b75e5000 rw-p 00000000 00:00 0
> b75e5000-b774b000 r-xp 00000000 08:01 131375     /lib/libc-2.11.3.so
> b774b000-b774c000 ---p 00166000 08:01 131375     /lib/libc-2.11.3.so
> b774c000-b774e000 r--p 00166000 08:01 131375     /lib/libc-2.11.3.so
> b774e000-b774f000 rw-p 00168000 08:01 131375     /lib/libc-2.11.3.so
> b774f000-b7752000 rw-p 00000000 00:00 0
> b7752000-b7755000 r-xp 00000000 08:01 131428     /lib/libdl-2.11.3.so
> b7755000-b7756000 r--p 00002000 08:01 131428     /lib/libdl-2.11.3.so
> b7756000-b7757000 rw-p 00003000 08:01 131428     /lib/libdl-2.11.3.so
> b7774000-b7775000 rw-p 00000000 00:00 0
> b7775000-b7794000 r-xp 00000000 08:01 154467     /lib/ld-2.11.3.so
> b7794000-b7795000 r--p 0001e000 08:01 154467     /lib/ld-2.11.3.so
> b7795000-b7796000 rw-p 0001f000 08:01 154467     /lib/ld-2.11.3.so
> bfa02000-bfa23000 rw-p 00000000 00:00 0          [stack]
> ffffe000-fffff000 r-xp 00000000 00:00 0          [vdso]
> Aborted
> 
> And If without -D_FORTIFY_SOURCE=2 in gcc, it works fine, so It's a
> bug in iproute2 which is not conforming to -D_FORTIFY_SOURCE=2
> restrictions.
> 

FORTIFY assumes we cant copy a string on alg.u.alg.alg_key !

This completely precludes 0-sized arrays

struct xfrm_algo {
        char            alg_name[64];
        unsigned int    alg_key_len;    /* in bits */
        char            alg_key[0];
};

struct {
      union {
          struct xfrm_algo alg;
          struct xfrm_algo_aead aead;
          struct xfrm_algo_auth auth;
      } u;
      char buf[XFRM_ALGO_KEY_BUF_SIZE];
} alg = {};

I would say its a FORTIFY bug. This kind of construct is perfectly
valid.