[PATCH 3.18 009/121] pidns: disable pid allocation if pid_ns_prepare_proc() is failed in alloc_pid()

[Greg Kroah-Hartman]

3.18-stable review patch.  If anyone has any objections, please let me know.

--

From: Kirill Tkhai 


[ Upstream commit 8896c23d2ef803f1883fea73117a435925c2b4c4 ]

alloc_pidmap() advances pid_namespace::last_pid.  When first pid
allocation fails, then next created process will have pid 2 and
pid_ns_prepare_proc() won't be called.  So, pid_namespace::proc_mnt will
never be initialized (not to mention that there won't be a child
reaper).

I saw crash stack of such case on kernel 3.10:

BUG: unable to handle kernel NULL pointer dereference at (null)
IP: proc_flush_task+0x8f/0x1b0
Call Trace:
release_task+0x3f/0x490
wait_consider_task.part.10+0x7ff/0xb00
do_wait+0x11f/0x280
SyS_wait4+0x7d/0x110

We may fix this by restore of last_pid in 0 or by prohibiting of futher
allocations.  Since there was a similar issue in Oleg Nesterov's commit
314a8ad0f18a ("pidns: fix free_pid() to handle the first fork failure").
and it was fixed via prohibiting allocation, let's follow this way, and
do the same.

Link: 
http://lkml.kernel.org/r/149201021004.4863.6762095011554287922.stgit@localhost.localdomain
Signed-off-by: Kirill Tkhai 
Acked-by: Cyrill Gorcunov 
Cc: Andrei Vagin 
Cc: Andreas Gruenbacher 
Cc: Kees Cook 
Cc: Michael Kerrisk 
Cc: Al Viro 
Cc: Oleg Nesterov 
Cc: Paul Moore 
Cc: Eric Biederman 
Cc: Andy Lutomirski 
Cc: Ingo Molnar 
Cc: Serge Hallyn 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Sasha Levin 
Signed-off-by: Greg Kroah-Hartman 
---
 kernel/pid.c |4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -316,8 +316,10 @@ struct pid *alloc_pid(struct pid_namespa
}
 
if (unlikely(is_child_reaper(pid))) {
-   if (pid_ns_prepare_proc(ns))
+   if (pid_ns_prepare_proc(ns)) {
+   disable_pid_allocation(ns);
goto out_free;
+   }
}
 
get_pid_ns(ns);

[PATCH 3.18 009/121] pidns: disable pid allocation if pid_ns_prepare_proc() is failed in alloc_pid()

[Greg Kroah-Hartman]

3.18-stable review patch.  If anyone has any objections, please let me know.

--

From: Kirill Tkhai 


[ Upstream commit 8896c23d2ef803f1883fea73117a435925c2b4c4 ]

alloc_pidmap() advances pid_namespace::last_pid.  When first pid
allocation fails, then next created process will have pid 2 and
pid_ns_prepare_proc() won't be called.  So, pid_namespace::proc_mnt will
never be initialized (not to mention that there won't be a child
reaper).

I saw crash stack of such case on kernel 3.10:

BUG: unable to handle kernel NULL pointer dereference at (null)
IP: proc_flush_task+0x8f/0x1b0
Call Trace:
release_task+0x3f/0x490
wait_consider_task.part.10+0x7ff/0xb00
do_wait+0x11f/0x280
SyS_wait4+0x7d/0x110

We may fix this by restore of last_pid in 0 or by prohibiting of futher
allocations.  Since there was a similar issue in Oleg Nesterov's commit
314a8ad0f18a ("pidns: fix free_pid() to handle the first fork failure").
and it was fixed via prohibiting allocation, let's follow this way, and
do the same.

Link: 
http://lkml.kernel.org/r/149201021004.4863.6762095011554287922.stgit@localhost.localdomain
Signed-off-by: Kirill Tkhai 
Acked-by: Cyrill Gorcunov 
Cc: Andrei Vagin 
Cc: Andreas Gruenbacher 
Cc: Kees Cook 
Cc: Michael Kerrisk 
Cc: Al Viro 
Cc: Oleg Nesterov 
Cc: Paul Moore 
Cc: Eric Biederman 
Cc: Andy Lutomirski 
Cc: Ingo Molnar 
Cc: Serge Hallyn 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Sasha Levin 
Signed-off-by: Greg Kroah-Hartman 
---
 kernel/pid.c |4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -316,8 +316,10 @@ struct pid *alloc_pid(struct pid_namespa
}
 
if (unlikely(is_child_reaper(pid))) {
-   if (pid_ns_prepare_proc(ns))
+   if (pid_ns_prepare_proc(ns)) {
+   disable_pid_allocation(ns);
goto out_free;
+   }
}
 
get_pid_ns(ns);