[CVE-2011-1593][Hardy][PATCH 1/2] next_pidmap: fix overflow condition, CVE-2011-1593

[Herton Ronaldo Krzesinski]

From: Linus Torvalds <torvalds at linux-foundation.org>

CVE-2011-1593

BugLink: https://bugs.launchpad.net/bugs/784727

Released until now with stable versions 2.6.27.59, 2.6.32.39, 2.6.33.12,
2.6.35.13, 2.6.38.4

next_pidmap() just quietly accepted whatever 'last' pid that was passed
in, which is not all that safe when one of the users is /proc.

Admittedly the proc code should do some sanity checking on the range
(and that will be the next commit), but that doesn't mean that the
helper functions should just do that pidmap pointer arithmetic without
checking the range of its arguments.

So clamp 'last' to PID_MAX_LIMIT.  The fact that we then do "last+1"
doesn't really matter, the for-loop does check against the end of the
pidmap array properly (it's only the actual pointer arithmetic overflow
case we need to worry about, and going one bit beyond isn't going to
overflow).

[ Use PID_MAX_LIMIT rather than pid_max as per Eric Biederman ]

Reported-by: Tavis Ormandy <taviso at cmpxchg8b.com>
Analyzed-by: Robert Święcki <robert at swiecki.net>
Cc: Eric W. Biederman <ebiederm at xmission.com>
Cc: Pavel Emelyanov <xemul at openvz.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
(backported from commit c78193e9c7bcbf25b8237ad0dec82f805c4ea69b upstream)
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski at canonical.com>
---
 .../openvz/patchset/0001-2.6.24-ovz002.patch       |    2 +-
 kernel/pid.c                                       |    5 ++++-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/debian/binary-custom.d/openvz/patchset/0001-2.6.24-ovz002.patch b/debian/binary-custom.d/openvz/patchset/0001-2.6.24-ovz002.patch
index 729b278..6a8a613 100644
--- a/debian/binary-custom.d/openvz/patchset/0001-2.6.24-ovz002.patch
+++ b/debian/binary-custom.d/openvz/patchset/0001-2.6.24-ovz002.patch
@@ -62556,7 +62556,7 @@ Index: kernel/kernel/pid.c
 +	return pid;
 +}
 +
- static int next_pidmap(struct pid_namespace *pid_ns, int last)
+ static int next_pidmap(struct pid_namespace *pid_ns, unsigned int last)
  {
  	int offset;
 @@ -198,6 +231,7 @@
diff --git a/kernel/pid.c b/kernel/pid.c
index f815455..29f0ac0 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -181,11 +181,14 @@ static int alloc_pidmap(struct pid_namespace *pid_ns)
 	return -1;
 }
 
-static int next_pidmap(struct pid_namespace *pid_ns, int last)
+static int next_pidmap(struct pid_namespace *pid_ns, unsigned int last)
 {
 	int offset;
 	struct pidmap *map, *end;
 
+	if (last >= PID_MAX_LIMIT)
+		return -1;
+
 	offset = (last + 1) & BITS_PER_PAGE_MASK;
 	map = &pid_ns->pidmap[(last + 1)/BITS_PER_PAGE];
 	end = &pid_ns->pidmap[PIDMAP_ENTRIES];
-- 
1.7.0.4