ptp: reduce stack usage when reading external time stamps

This patch removes the large buffer from the stack of the read file
operation and replaces it with a kmalloced buffer.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 17 insertions, 5 deletions

diff --git a/drivers/ptp/ptp_chardev.c b/drivers/ptp/ptp_chardev.c
index 4f8ae8057a7e..9d7542efb175 100644
--- a/drivers/ptp/ptp_chardev.c
+++ b/drivers/ptp/ptp_chardev.c
@@ -21,6 +21,7 @@
 #include <linux/posix-clock.h>
 #include <linux/poll.h>
 #include <linux/sched.h>
+#include <linux/slab.h>
 
 #include "ptp_private.h"
 
@@ -136,20 +137,23 @@ unsigned int ptp_poll(struct posix_clock *pc, struct file *fp, poll_table *wait)
         return queue_cnt(&ptp->tsevq) ? POLLIN : 0;
 }
 
+#define EXTTS_BUFSIZE (PTP_BUF_TIMESTAMPS * sizeof(struct ptp_extts_event))
+
 ssize_t ptp_read(struct posix_clock *pc,
                  uint rdflags, char __user *buf, size_t cnt)
 {
         struct ptp_clock *ptp = container_of(pc, struct ptp_clock, clock);
         struct timestamp_event_queue *queue = &ptp->tsevq;
-        struct ptp_extts_event event[PTP_BUF_TIMESTAMPS];
+        struct ptp_extts_event *event;
         unsigned long flags;
         size_t qcnt, i;
+        int result;
 
         if (cnt % sizeof(struct ptp_extts_event) != 0)
                 return -EINVAL;
 
-        if (cnt > sizeof(event))
-                cnt = sizeof(event);
+        if (cnt > EXTTS_BUFSIZE)
+                cnt = EXTTS_BUFSIZE;
 
         cnt = cnt / sizeof(struct ptp_extts_event);
 
@@ -167,6 +171,12 @@ ssize_t ptp_read(struct posix_clock *pc,
                 return -ENODEV;
         }
 
+        event = kmalloc(EXTTS_BUFSIZE, GFP_KERNEL);
+        if (!event) {
+                mutex_unlock(&ptp->tsevq_mux);
+                return -ENOMEM;
+        }
+
         spin_lock_irqsave(&queue->lock, flags);
 
         qcnt = queue_cnt(queue);
@@ -185,8 +195,10 @@ ssize_t ptp_read(struct posix_clock *pc,
 
         mutex_unlock(&ptp->tsevq_mux);
 
+        result = cnt;
         if (copy_to_user(buf, event, cnt))
-                return -EFAULT;
+                result = -EFAULT;
 
-        return cnt;
+        kfree(event);
+        return result;
 }