tracing: do not return EFAULT if read copied anything

Impact: fix trace read to conform to standards

Andrew Morton, Theodore Tso and H. Peter Anvin brought to my attention
that a userspace read should not return -EFAULT if it succeeded in
copying anything. It should only return -EFAULT if it failed to copy
at all.

This patch modifies the check of copy_from_user and updates the return
code appropriately.

I also used H. Peter Anvin's short cut rule to just test ret == count.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index ab5cbcae43a1ce511c8455909558a135657d0348..57155dc53530d2114f79b85e290bbbc685b661a4 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -346,6 +346,9 @@ ssize_t trace_seq_to_user(struct trace_seq *s, char __user *ubuf, size_t cnt)
        int len;
        int ret;
 
+       if (!cnt)
+               return 0;
+
        if (s->len <= s->readpos)
                return -EBUSY;
 
@@ -353,9 +356,11 @@ ssize_t trace_seq_to_user(struct trace_seq *s, char __user *ubuf, size_t cnt)
        if (cnt > len)
                cnt = len;
        ret = copy_to_user(ubuf, s->buffer + s->readpos, cnt);
-       if (ret)
+       if (ret == cnt)
                return -EFAULT;
 
+       cnt -= ret;
+
        s->readpos += len;
        return cnt;
 }
@@ -3049,6 +3054,9 @@ tracing_buffers_read(struct file *filp, char __user *ubuf,
        ssize_t ret;
        size_t size;
 
+       if (!count)
+               return 0;
+
        /* Do we have previous read data to read? */
        if (info->read < PAGE_SIZE)
                goto read;
@@ -3073,8 +3081,10 @@ read:
                size = count;
 
        ret = copy_to_user(ubuf, info->spare + info->read, size);
-       if (ret)
+       if (ret == size)
                return -EFAULT;
+       size -= ret;
+
        *ppos += size;
        info->read += size;