next_pidmap: fix overflow condition

commit c78193e9c7bcbf25b8237ad0dec82f805c4ea69b upstream.

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@cmpxchg8b.com>
Analyzed-by: Robert Święcki <robert@swiecki.net>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/include/linux/pid.h b/include/linux/pid.h
index 49f1c2f66e951bc7e226a5809450af8714c80473..ec9f2df57f1b8857e0e11d417bd697d947d19935 100644 (file)
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -117,7 +117,7 @@ extern struct pid *find_vpid(int nr);
  */
 extern struct pid *find_get_pid(int nr);
 extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
-int next_pidmap(struct pid_namespace *pid_ns, int last);
+int next_pidmap(struct pid_namespace *pid_ns, unsigned int last);
 
 extern struct pid *alloc_pid(struct pid_namespace *ns);
 extern void free_pid(struct pid *pid);

diff --git a/kernel/pid.c b/kernel/pid.c
index aebb30d9c233df40876afa35ef21cc5c306590a1..af8dbf7dfe3ac3fceb30ebb0ef07c2d9b9bd69c4 100644 (file)
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -183,11 +183,14 @@ static int alloc_pidmap(struct pid_namespace *pid_ns)
        return -1;
 }
 
-int next_pidmap(struct pid_namespace *pid_ns, int last)
+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];