From: Jeff Dike <jdike@addtoit.com>
Date: Tue, 5 Feb 2008 06:31:10 +0000 (-0800)
Subject: uml: don't kill pid 0
X-Git-Tag: v2.6.25-rc1~818
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=00a905e6145ba200308a6a13e00248b85c600bd0;p=linux-2.6

uml: don't kill pid 0

A bit of defensive programming - during development, it ocassionally
happens that a call to init_new_context is missed, resulting in
context holding a host pid of zero.  When that address space is torn
down, destroy_context does a kill(0), which instantly kills the whole
UML without any errors whatsoever.

This patch add a check for pids less than 2, to also catch 1 and
negative pids.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

diff --git a/arch/um/kernel/skas/mmu.c b/arch/um/kernel/skas/mmu.c
index e8dc8540d4..78b3e9f69d 100644
--- a/arch/um/kernel/skas/mmu.c
+++ b/arch/um/kernel/skas/mmu.c
@@ -164,8 +164,20 @@ void destroy_context(struct mm_struct *mm)
 
 	if (proc_mm)
 		os_close_file(mmu->id.u.mm_fd);
-	else
+	else {
+		/*
+		 * If init_new_context wasn't called, this will be
+		 * zero, resulting in a kill(0), which will result in the
+		 * whole UML suddenly dying.  Also, cover negative and
+		 * 1 cases, since they shouldn't happen either.
+		 */
+		if (mmu->id.u.pid < 2) {
+			printk(KERN_ERR "corrupt mm_context - pid = %d\n",
+			       mmu->id.u.pid);
+			return;
+		}
 		os_kill_ptraced_process(mmu->id.u.pid, 1);
+	}
 
 	if (skas_needs_stub)
 		free_page(mmu->id.stack);