Re: [PATCH 1/2] ipc, msg: fix message length check for negative values

[Linus Torvalds]

On Sat, Nov 2, 2013 at 2:26 PM, Mathias Krause <minipli@xxxxxxxxxxxxxx> wrote:
> On 64 bit systems the test for negative message sizes is bogus as the
> size, which may be positive when evaluated as a long, will get truncated
> to an int when passed to load_msg().

Quite frankly, wouldn't it be much nicer to just fix "load_msg()" instead?

Using "size_t" also gets rid of the games we play with DATALEN_MSG/SEG.

IOW, something like the attached..

Of course, we *also* should fix ns->msg_ctlmax to make clear you can't
use negative numbers there. No question about that. I think it would
be better to even avoid INT_MAX, because there are memory use concerns
and CPU usage ones too (we generate that list of
smaller-than-page-size fragments).

Hmm?

              Linus
 include/linux/ipc_namespace.h |  6 +++---
 ipc/msgutil.c                 | 14 +++++++-------
 ipc/util.h                    |  4 ++--
 3 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/include/linux/ipc_namespace.h b/include/linux/ipc_namespace.h
index 19c19a5eee29..f6c82de12541 100644
--- a/include/linux/ipc_namespace.h
+++ b/include/linux/ipc_namespace.h
@@ -34,9 +34,9 @@ struct ipc_namespace {
 	int		sem_ctls[4];
 	int		used_sems;
 
-	int		msg_ctlmax;
-	int		msg_ctlmnb;
-	int		msg_ctlmni;
+	unsigned int	msg_ctlmax;
+	unsigned int	msg_ctlmnb;
+	unsigned int	msg_ctlmni;
 	atomic_t	msg_bytes;
 	atomic_t	msg_hdrs;
 	int		auto_msgmni;
diff --git a/ipc/msgutil.c b/ipc/msgutil.c
index 491e71f2a1b8..3cd9cb959c74 100644
--- a/ipc/msgutil.c
+++ b/ipc/msgutil.c
@@ -41,15 +41,15 @@ struct msg_msgseg {
 	/* the next part of the message follows immediately */
 };
 
-#define DATALEN_MSG	(int)(PAGE_SIZE-sizeof(struct msg_msg))
-#define DATALEN_SEG	(int)(PAGE_SIZE-sizeof(struct msg_msgseg))
+#define DATALEN_MSG	(PAGE_SIZE-sizeof(struct msg_msg))
+#define DATALEN_SEG	(PAGE_SIZE-sizeof(struct msg_msgseg))
 
 
-static struct msg_msg *alloc_msg(int len)
+static struct msg_msg *alloc_msg(size_t len)
 {
 	struct msg_msg *msg;
 	struct msg_msgseg **pseg;
-	int alen;
+	size_t alen;
 
 	alen = min(len, DATALEN_MSG);
 	msg = kmalloc(sizeof(*msg) + alen, GFP_KERNEL);
@@ -80,7 +80,7 @@ out_err:
 	return NULL;
 }
 
-struct msg_msg *load_msg(const void __user *src, int len)
+struct msg_msg *load_msg(const void __user *src, size_t len)
 {
 	struct msg_msg *msg;
 	struct msg_msgseg *seg;
@@ -147,9 +147,9 @@ struct msg_msg *copy_msg(struct msg_msg *src, struct msg_msg *dst)
 	return ERR_PTR(-ENOSYS);
 }
 #endif
-int store_msg(void __user *dest, struct msg_msg *msg, int len)
+int store_msg(void __user *dest, struct msg_msg *msg, size_t len)
 {
-	int alen;
+	size_t alen;
 	struct msg_msgseg *seg;
 
 	alen = min(len, DATALEN_MSG);
diff --git a/ipc/util.h b/ipc/util.h
index f2f5036f2eed..59d78aa94987 100644
--- a/ipc/util.h
+++ b/ipc/util.h
@@ -148,9 +148,9 @@ int ipc_parse_version (int *cmd);
 #endif
 
 extern void free_msg(struct msg_msg *msg);
-extern struct msg_msg *load_msg(const void __user *src, int len);
+extern struct msg_msg *load_msg(const void __user *src, size_t len);
 extern struct msg_msg *copy_msg(struct msg_msg *src, struct msg_msg *dst);
-extern int store_msg(void __user *dest, struct msg_msg *msg, int len);
+extern int store_msg(void __user *dest, struct msg_msg *msg, size_t len);
 
 extern void recompute_msgmni(struct ipc_namespace *);