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authorMeng Xu <mengxu.gatech@gmail.com>2017-09-19 21:49:55 -0400
committerDavid S. Miller <davem@davemloft.net>2017-09-20 16:01:36 -0700
commit02388bf87f72e1d47174cd8f81c34443920eb5a0 (patch)
tree84b4405a24c99a5c49b709978c4bb653fe225f0f
parente24ee2780a1d6786b94139ebf95b44c9ae62bf13 (diff)
isdn/i4l: fetch the ppp_write buffer in one shot
In isdn_ppp_write(), the header (i.e., protobuf) of the buffer is fetched twice from userspace. The first fetch is used to peek at the protocol of the message and reset the huptimer if necessary; while the second fetch copies in the whole buffer. However, given that buf resides in userspace memory, a user process can race to change its memory content across fetches. By doing so, we can either avoid resetting the huptimer for any type of packets (by first setting proto to PPP_LCP and later change to the actual type) or force resetting the huptimer for LCP packets. This patch changes this double-fetch behavior into two single fetches decided by condition (lp->isdn_device < 0 || lp->isdn_channel <0). A more detailed discussion can be found at https://marc.info/?l=linux-kernel&m=150586376926123&w=2 Signed-off-by: Meng Xu <mengxu.gatech@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--drivers/isdn/i4l/isdn_ppp.c37
1 files changed, 25 insertions, 12 deletions
diff --git a/drivers/isdn/i4l/isdn_ppp.c b/drivers/isdn/i4l/isdn_ppp.c
index 6c44609fd83a..cd2b3c69771a 100644
--- a/drivers/isdn/i4l/isdn_ppp.c
+++ b/drivers/isdn/i4l/isdn_ppp.c
@@ -825,7 +825,6 @@ isdn_ppp_write(int min, struct file *file, const char __user *buf, int count)
isdn_net_local *lp;
struct ippp_struct *is;
int proto;
- unsigned char protobuf[4];
is = file->private_data;
@@ -839,24 +838,28 @@ isdn_ppp_write(int min, struct file *file, const char __user *buf, int count)
if (!lp)
printk(KERN_DEBUG "isdn_ppp_write: lp == NULL\n");
else {
- /*
- * Don't reset huptimer for
- * LCP packets. (Echo requests).
- */
- if (copy_from_user(protobuf, buf, 4))
- return -EFAULT;
- proto = PPP_PROTOCOL(protobuf);
- if (proto != PPP_LCP)
- lp->huptimer = 0;
+ if (lp->isdn_device < 0 || lp->isdn_channel < 0) {
+ unsigned char protobuf[4];
+ /*
+ * Don't reset huptimer for
+ * LCP packets. (Echo requests).
+ */
+ if (copy_from_user(protobuf, buf, 4))
+ return -EFAULT;
+
+ proto = PPP_PROTOCOL(protobuf);
+ if (proto != PPP_LCP)
+ lp->huptimer = 0;
- if (lp->isdn_device < 0 || lp->isdn_channel < 0)
return 0;
+ }
if ((dev->drv[lp->isdn_device]->flags & DRV_FLAG_RUNNING) &&
lp->dialstate == 0 &&
(lp->flags & ISDN_NET_CONNECTED)) {
unsigned short hl;
struct sk_buff *skb;
+ unsigned char *cpy_buf;
/*
* we need to reserve enough space in front of
* sk_buff. old call to dev_alloc_skb only reserved
@@ -869,11 +872,21 @@ isdn_ppp_write(int min, struct file *file, const char __user *buf, int count)
return count;
}
skb_reserve(skb, hl);
- if (copy_from_user(skb_put(skb, count), buf, count))
+ cpy_buf = skb_put(skb, count);
+ if (copy_from_user(cpy_buf, buf, count))
{
kfree_skb(skb);
return -EFAULT;
}
+
+ /*
+ * Don't reset huptimer for
+ * LCP packets. (Echo requests).
+ */
+ proto = PPP_PROTOCOL(cpy_buf);
+ if (proto != PPP_LCP)
+ lp->huptimer = 0;
+
if (is->debug & 0x40) {
printk(KERN_DEBUG "ppp xmit: len %d\n", (int) skb->len);
isdn_ppp_frame_log("xmit", skb->data, skb->len, 32, is->unit, lp->ppp_slot);