linux-kernel - Re: [REVIEW][PATCH 0/3] Fixing ptrace vs exec vs userns interactions

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Date:   Sat, 19 Nov 2016 10:33:26 +0100
From:   Willy Tarreau <w@....eu>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Linux Containers <containers@...ts.linux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        Michal Hocko <mhocko@...nel.org>, Jann Horn <jann@...jh.net>,
        Kees Cook <keescook@...omium.org>,
        Andy Lutomirski <luto@...capital.net>
Subject: Re: [REVIEW][PATCH 0/3] Fixing ptrace vs exec vs userns interactions

On Sat, Nov 19, 2016 at 10:28:04AM +0100, Willy Tarreau wrote:
> On Sat, Nov 19, 2016 at 08:17:00AM +0100, Willy Tarreau wrote:
> > Hi Eric,
> > 
> > On Thu, Nov 17, 2016 at 11:02:47AM -0600, Eric W. Biederman wrote:
> > > 
> > > With everyone heading to Kernel Summit and Plumbers I put this set of
> > > patches down temporarily.   Now is the time to take it back up and to
> > > make certain I am not missing something stupid in this set of patches.
> > 
> > I couldn't get your patch set to apply to any of the kernels I tried,
> > I manually adjusted some parts but the second one has too many rejects.
> > What kernel should I apply this to ? Or maybe some preliminary patches
> > are needed ?
> 
> OK I finally managed to get it to work on top of 4.8.9 (required less changes
> than master). I also had to drop the user_ns changes since there's no such
> user_ns in mm_struct there.
> 
> I could run a test on it, that looks reasonable :
> 
> FS:
> 
> admin@vm:~$ strace -e trace=fstat,uname,ioctl,open uname
> open(0x7ffd01bbeeb0, O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
> open(0x7ffd01bbeeb0, O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
> open(0x7ffd01bbeeb0, O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
> open(0x7ffd01bbeeb0, O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
> open(0x7f3f9a1663e3, O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
> open(0x7ffd01bbeeb0, O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
> open(0x7ffd01bbeeb0, O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
> open(0x7ffd01bbeeb0, O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
> open(0x7ffd01bbeeb0, O_RDONLY|O_CLOEXEC) = 3
> fstat(3, {...})                         = 0
> open(0x7ffd01bbee80, O_RDONLY|O_CLOEXEC) = 3
> fstat(3, {...})                         = 0
> uname({...})                            = 0
> fstat(1, {...})                         = 0
> ioctl(1, SNDCTL_TMR_TIMEBASE or TCGETS, 0x7ffd01bbf400) = 0
> 
> admin@vm:~$ sudo strace -e trace=fstat,uname,ioctl,open uname
> open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
> open("/lib64/tls/x86_64/libpthread.so.0", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
> open("/lib64/tls/libpthread.so.0", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
> open("/lib64/x86_64/libpthread.so.0", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
> open("/lib64/libpthread.so.0", O_RDONLY|O_CLOEXEC) = 3
> fstat(3, {st_mode=S_IFREG|0555, st_size=101312, ...}) = 0
> open("/lib64/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
> fstat(3, {st_mode=S_IFREG|0555, st_size=1479016, ...}) = 0
> uname({sys="Linux", node="vm", ...})    = 0
> fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(4, 64), ...}) = 0
> ioctl(1, SNDCTL_TMR_TIMEBASE or TCGETS, {B9600 opost isig icanon echo ...}) = 0
> 
> Network:
> 
> admin@vm:~$ strace -e trace=socket,setsockopt,connect /tmp/nc 198.18.3 22
> socket(PF_FILE, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 3
> connect(3, {...}, 110)                  = -1 ENOENT (No such file or directory)
> socket(PF_FILE, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 3
> connect(3, {...}, 110)                  = -1 ENOENT (No such file or directory)
> socket(PF_INET, SOCK_STREAM, IPPROTO_TCP) = 3
> setsockopt(3, SOL_SOCKET, SO_REUSEADDR, 0x7ffd2c26bdbc, 4) = 0
> connect(3, {...}, 16)                   = 0
> 
> admin@vm:~$ sudo strace -e trace=socket,setsockopt,connect /tmp/nc 198.18.3 22
> socket(PF_FILE, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 3
> connect(3, {sa_family=AF_FILE, path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
> socket(PF_FILE, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 3
> connect(3, {sa_family=AF_FILE, path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
> socket(PF_INET, SOCK_STREAM, IPPROTO_TCP) = 3
> setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
> connect(3, {sa_family=AF_INET, sin_port=htons(22), sin_addr=inet_addr("198.18.0.3")}, 16) = 0
> 
> So in short now we can at least see what syscall fails eventhough we can't
> know why. I think it can be an acceptable trade-off.

I also tested with gdb and it behaves as desired :

admin@vm:~$ sleep 100000 &
[1] 1615
admin@vm:~$ /tmp/gdb-x86_64 -q -p 1615
Attaching to process 1615
ptrace: Operation not permitted.
(gdb) quit

admin@vm:~$ sudo cp /bin/sleep /var/tmp/
admin@vm:~$ sudo chmod 755 /var/tmp/sleep 
admin@vm:~$ /tmp/sleep 100000 &
[1] 1620
admin@vm:~$ /tmp/gdb-x86_64 -q -p 1620
Attaching to process 1620
Reading symbols from /var/tmp/sleep...(no debugging symbols found)...done.
(...)
0x00007f6723d561b0 in nanosleep () from /lib64/libpthread.so.0
(gdb) quit

Willy