[patch] RDS: fix an integer overflow check

"len" is an int.  We verified that len was postive already.  Since
PAGE_SIZE is specified as an unsigned long, the type it promoted to
unsigned and the condition is never true.

I'm not sure this check is actually needed.  It might be that we could
just remove it?

Signed-off-by: Dan Carpenter <redacted>

diff --git a/net/rds/info.c b/net/rds/info.c
index 9a6b4f6..4d62618 100644
--- a/net/rds/info.c
+++ b/net/rds/info.c

@@ -176,7 +176,7 @@ int rds_info_getsockopt(struct socket *sock, int optname, char __user *optval,
 
 	/* check for all kinds of wrapping and the like */
 	start = (unsigned long)optval;
-	if (len < 0 || len + PAGE_SIZE - 1 < len || start + len < start) {
+	if (len < 0 || len > INT_MAX - (PAGE_SIZE - 1) || start + len < start) {
 		ret = -EINVAL;
 		goto out;
 	}

On 10/12/2012 03:31 PM, Dan Carpenter wrote:

Looks the original thought is to check up len + (PAGE_SIZE - 1) < len to avoid integer overflow, but lack of a "()".

However, we only have one add operation in this function which were shown as following:
        nr_pages = (PAGE_ALIGN(start + len) - (start & PAGE_MASK))
                        >> PAGE_SHIFT;

I also gone through the call chains, there is no other (start + len) operations for all transport, I think it's safe to remove this check up if so.

Thanks,
-Jeff

+	if (len < 0 || len > INT_MAX - (PAGE_SIZE - 1) || start + len < start) {
  		ret = -EINVAL;
  		goto out;
  	}
--
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On 10/13/2012 09:25 PM, Jeff Liu wrote:

On 10/12/2012 03:31 PM, Dan Carpenter wrote:

quoted

"len" is an int.  We verified that len was postive already.  Since
PAGE_SIZE is specified as an unsigned long, the type it promoted to
unsigned and the condition is never true.

I'm not sure this check is actually needed.  It might be that we could
just remove it?

Signed-off-by: Dan Carpenter <redacted>

diff --git a/net/rds/info.c b/net/rds/info.c
index 9a6b4f6..4d62618 100644
--- a/net/rds/info.c
+++ b/net/rds/info.c

@@ -176,7 +176,7 @@ int rds_info_getsockopt(struct socket *sock, int optname, char __user *optval,
   
   	/* check for all kinds of wrapping and the like */
   	start = (unsigned long)optval;
-	if (len < 0 || len + PAGE_SIZE - 1 < len || start + len < start) {

Looks the original thought is to check up len + (PAGE_SIZE - 1) < len to
avoid integer overflow, but lack of a "()".

However, we only have one add operation in this function which were
shown as following:
          nr_pages = (PAGE_ALIGN(start + len) - (start & PAGE_MASK))
                          >> PAGE_SHIFT;

I also gone through the call chains, there is no other (start + len)

Sorry, here is a typo.  "start + len" is already well-checked.
Actually, I means there is no other "len + (PAGE_SIZE - 1)" operations.

Thanks,
-Jeff

operations for all transport, I think it's safe to remove this check up
if so.

Thanks,
-Jeff

quoted

+	if (len < 0 || len > INT_MAX - (PAGE_SIZE - 1) || start + len < start) {
   		ret = -EINVAL;
   		goto out;
   	}
--
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