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Subject[PATCH 2/7] tracing: do not return EFAULT if read copied anything
From: Steven Rostedt <srostedt@redhat.com>

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>
---
kernel/trace/trace.c | 14 ++++++++++++--
1 files changed, 12 insertions(+), 2 deletions(-)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index ab5cbca..57155dc 100644
--- 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;

--
1.6.1.3
--


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