linux-stable.git/fs/proc/array.c, branch v3.2.97

ptrace: use fsuid, fsgid, effective creds for fs access checks

2017-09-15T17:30:57+00:00

commit caaee6234d05a58c5b4d05e7bf766131b810a657 upstream.

By checking the effective credentials instead of the real UID / permitted
capabilities, ensure that the calling process actually intended to use its
credentials.

To ensure that all ptrace checks use the correct caller credentials (e.g.
in case out-of-tree code or newly added code omits the PTRACE_MODE_*CREDS
flag), use two new flags and require one of them to be set.

The problem was that when a privileged task had temporarily dropped its
privileges, e.g.  by calling setreuid(0, user_uid), with the intent to
perform following syscalls with the credentials of a user, it still passed
ptrace access checks that the user would not be able to pass.

While an attacker should not be able to convince the privileged task to
perform a ptrace() syscall, this is a problem because the ptrace access
check is reused for things in procfs.

In particular, the following somewhat interesting procfs entries only rely
on ptrace access checks:

 /proc/$pid/stat - uses the check for determining whether pointers
     should be visible, useful for bypassing ASLR
 /proc/$pid/maps - also useful for bypassing ASLR
 /proc/$pid/cwd - useful for gaining access to restricted
     directories that contain files with lax permissions, e.g. in
     this scenario:
     lrwxrwxrwx root root /proc/13020/cwd -> /root/foobar
     drwx------ root root /root
     drwxr-xr-x root root /root/foobar
     -rw-r--r-- root root /root/foobar/secret

Therefore, on a system where a root-owned mode 6755 binary changes its
effective credentials as described and then dumps a user-specified file,
this could be used by an attacker to reveal the memory layout of root's
processes or reveal the contents of files he is not allowed to access
(through /proc/$pid/cwd).

[akpm@linux-foundation.org: fix warning]
Signed-off-by: Jann Horn 
Acked-by: Kees Cook 
Cc: Casey Schaufler 
Cc: Oleg Nesterov 
Cc: Ingo Molnar 
Cc: James Morris 
Cc: "Serge E. Hallyn" 
Cc: Andy Shevchenko 
Cc: Andy Lutomirski 
Cc: Al Viro 
Cc: "Eric W. Biederman" 
Cc: Willy Tarreau 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman 
[bwh: Backported to 3.2:
 - Drop changes to kcmp, procfs map_files, procfs has_pid_permissions()
 - Keep using uid_t, gid_t and == operator for IDs
 - Adjust context]
Signed-off-by: Ben Hutchings

proc: pid/status: show all supplementary groups

2013-01-03T03:33:43+00:00

commit 8d238027b87e654be552eabdf492042a34c5c300 upstream.

We display a list of supplementary group for each process in
/proc//status.  However, we show only the first 32 groups, not all of
them.

Although this is rare, but sometimes processes do have more than 32
supplementary groups, and this kernel limitation breaks user-space apps
that rely on the group list in /proc//status.

Number 32 comes from the internal NGROUPS_SMALL macro which defines the
length for the internal kernel "small" groups buffer.  There is no
apparent reason to limit to this value.

This patch removes the 32 groups printing limit.

The Linux kernel limits the amount of supplementary groups by NGROUPS_MAX,
which is currently set to 65536.  And this is the maximum count of groups
we may possibly print.

Signed-off-by: Artem Bityutskiy 
Acked-by: Serge E. Hallyn 
Acked-by: Kees Cook 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings

ptrace: s/tracehook_tracer_task()/ptrace_parent()/

2011-06-22T17:26:29+00:00

tracehook.h is on the way out.  Rename tracehook_tracer_task() to
ptrace_parent() and move it from tracehook.h to ptrace.h.

Signed-off-by: Tejun Heo 
Cc: Christoph Hellwig 
Cc: John Johansen 
Cc: Stephen Smalley 
Signed-off-by: Oleg Nesterov

proc: constify status array

2011-05-27T00:12:36+00:00

No need for this local array to be writable, so mark it const.

Signed-off-by: Mike Frysinger 
Cc: Alexey Dobriyan 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

proc: protect mm start_code/end_code in /proc/pid/stat

2011-03-24T02:46:37+00:00

While mm->start_stack was protected from cross-uid viewing (commit
f83ce3e6b02d5 ("proc: avoid information leaks to non-privileged
processes")), the start_code and end_code values were not.  This would
allow the text location of a PIE binary to leak, defeating ASLR.

Note that the value "1" is used instead of "0" for a protected value since
"ps", "killall", and likely other readers of /proc/pid/stat, take
start_code of "0" to mean a kernel thread and will misbehave.  Thanks to
Brad Spengler for pointing this out.

Addresses CVE-2011-0726

Signed-off-by: Kees Cook 
Cc: 
Cc: Alexey Dobriyan 
Cc: David Howells 
Cc: Eugene Teo 
Cc: Martin Schwidefsky 
Cc: Brad Spengler 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

s390: remove task_show_regs

2011-02-15T15:34:16+00:00

task_show_regs used to be a debugging aid in the early bringup days
of Linux on s390. /proc//status is a world readable file, it
is not a good idea to show the registers of a process. The only
correct fix is to remove task_show_regs.

Reported-by: Al Viro 
Signed-off-by: Martin Schwidefsky 
Signed-off-by: Linus Torvalds

proc: use seq_puts()/seq_putc() where possible

2011-01-13T16:03:16+00:00

For string without format specifiers, use seq_puts().
For seq_printf("\n"), use seq_putc('\n').

   text	   data	    bss	    dec	    hex	filename
  61866	    488	    112	  62466	   f402	fs/proc/proc.o
  61729	    488	    112	  62329	   f379	fs/proc/proc.o
  ----------------------------------------------------
  			   -139

Signed-off-by: Alexey Dobriyan 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

proc: use unsigned long inside /proc/*/statm

2011-01-13T16:03:16+00:00

/proc/*/statm code needlessly truncates data from unsigned long to int.
One needs only 8+ TB of RAM to make truncation visible.

Signed-off-by: Alexey Dobriyan 
Reviewed-by: WANG Cong 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

CRED: Fix get_task_cred() and task_state() to not resurrect dead credentials

2010-07-29T22:16:17+00:00

It's possible for get_task_cred() as it currently stands to 'corrupt' a set of
credentials by incrementing their usage count after their replacement by the
task being accessed.

What happens is that get_task_cred() can race with commit_creds():

	TASK_1			TASK_2			RCU_CLEANER
	-->get_task_cred(TASK_2)
	rcu_read_lock()
	__cred = __task_cred(TASK_2)
				-->commit_creds()
				old_cred = TASK_2->real_cred
				TASK_2->real_cred = ...
				put_cred(old_cred)
				  call_rcu(old_cred)
		[__cred->usage == 0]
	get_cred(__cred)
		[__cred->usage == 1]
	rcu_read_unlock()
							-->put_cred_rcu()
							[__cred->usage == 1]
							panic()

However, since a tasks credentials are generally not changed very often, we can
reasonably make use of a loop involving reading the creds pointer and using
atomic_inc_not_zero() to attempt to increment it if it hasn't already hit zero.

If successful, we can safely return the credentials in the knowledge that, even
if the task we're accessing has released them, they haven't gone to the RCU
cleanup code.

We then change task_state() in procfs to use get_task_cred() rather than
calling get_cred() on the result of __task_cred(), as that suffers from the
same problem.

Without this change, a BUG_ON in __put_cred() or in put_cred_rcu() can be
tripped when it is noticed that the usage count is not zero as it ought to be,
for example:

kernel BUG at kernel/cred.c:168!
invalid opcode: 0000 [#1] SMP
last sysfs file: /sys/kernel/mm/ksm/run
CPU 0
Pid: 2436, comm: master Not tainted 2.6.33.3-85.fc13.x86_64 #1 0HR330/OptiPlex
745
RIP: 0010:[]  [] __put_cred+0xc/0x45
RSP: 0018:ffff88019e7e9eb8  EFLAGS: 00010202
RAX: 0000000000000001 RBX: ffff880161514480 RCX: 00000000ffffffff
RDX: 00000000ffffffff RSI: ffff880140c690c0 RDI: ffff880140c690c0
RBP: ffff88019e7e9eb8 R08: 00000000000000d0 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000040 R12: ffff880140c690c0
R13: ffff88019e77aea0 R14: 00007fff336b0a5c R15: 0000000000000001
FS:  00007f12f50d97c0(0000) GS:ffff880007400000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f8f461bc000 CR3: 00000001b26ce000 CR4: 00000000000006f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process master (pid: 2436, threadinfo ffff88019e7e8000, task ffff88019e77aea0)
Stack:
 ffff88019e7e9ec8 ffffffff810698cd ffff88019e7e9ef8 ffffffff81069b45
<0> ffff880161514180 ffff880161514480 ffff880161514180 0000000000000000
<0> ffff88019e7e9f28 ffffffff8106aace 0000000000000001 0000000000000246
Call Trace:
 [] put_cred+0x13/0x15
 [] commit_creds+0x16b/0x175
 [] set_current_groups+0x47/0x4e
 [] sys_setgroups+0xf6/0x105
 [] system_call_fastpath+0x16/0x1b
Code: 48 8d 71 ff e8 7e 4e 15 00 85 c0 78 0b 8b 75 ec 48 89 df e8 ef 4a 15 00
48 83 c4 18 5b c9 c3 55 8b 07 8b 07 48 89 e5 85 c0 74 04 <0f> 0b eb fe 65 48 8b
04 25 00 cc 00 00 48 3b b8 58 04 00 00 75
RIP  [] __put_cred+0xc/0x45
 RSP 
---[ end trace df391256a100ebdd ]---

Signed-off-by: David Howells 
Acked-by: Jiri Olsa 
Signed-off-by: Linus Torvalds

proc: get_nr_threads() doesn't need ->siglock any longer

2010-05-27T16:12:47+00:00

Now that task->signal can't go away get_nr_threads() doesn't need
->siglock to read signal->count.

Also, make it inline, move into sched.h, and convert 2 other proc users of
signal->count to use this (now trivial) helper.

Henceforth get_nr_threads() is the only valid user of signal->count, we
are ready to turn it into "int nr_threads" or, perhaps, kill it.

Signed-off-by: Oleg Nesterov 
Cc: Alexey Dobriyan 
Cc: David Howells 
Cc: "Eric W. Biederman" 
Acked-by: Roland McGrath 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds