blktrace: NUL-terminate user space messages

Impact: fix corrupted blkparse output

Make sure messages from user space are NUL-terminated strings,
otherwise we could dump random memory to the block trace file.

Additionally, I've limited the message to BLK_TN_MAX_MSG-1
characters, because the last character would be stripped by
vscnprintf anyway.

Signed-off-by: Carl Henrik Lunde <chlunde@ping.uio.no>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: "Alan D. Brunelle" <alan.brunelle@hp.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <20090403122714.GT5178@kernel.dk>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 3 insertions, 2 deletions

diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index 947c5b3f90c4..a400b861fad3 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -327,10 +327,10 @@ static ssize_t blk_msg_write(struct file *filp, const char __user *buffer,
         char *msg;
         struct blk_trace *bt;
 
-        if (count > BLK_TN_MAX_MSG)
+        if (count > BLK_TN_MAX_MSG - 1)
                 return -EINVAL;
 
-        msg = kmalloc(count, GFP_KERNEL);
+        msg = kmalloc(count + 1, GFP_KERNEL);
         if (msg == NULL)
                 return -ENOMEM;
 
@@ -339,6 +339,7 @@ static ssize_t blk_msg_write(struct file *filp, const char __user *buffer,
                 return -EFAULT;
         }
 
+        msg[count] = '\0';
         bt = filp->private_data;
         __trace_note_message(bt, "%s", msg);
         kfree(msg);