Commit c9b3febc authored by Jesper Juhl's avatar Jesper Juhl Committed by Linus Torvalds

Fix a use after free bug in kernel->userspace relay file support

Coverity spotted what looks like a real possible case of using a variable
after it has been freed.  The problem is in
kernel/relay.c::relay_open_buf()

If the code hits "goto free_buf;" it ends up in this code :

  free_buf:
    	relay_destroy_buf(buf);	<--- calls kfree() on 'buf'.
  free_name:
   	kfree(tmpname);
  end:
  	return buf;		<-- use after free of 'buf'.

I read through the callers and they all handle a NULL return from this
function as an error (and hitting the 'free_buf' label only happens on
failure to chan->cb->create_buf_file(), so that looks like a clear error to
me).

The patch simply sets 'buf' to NULL after the call to
relay_destroy_buf(buf); - as far as I can see that should take care of the
problem.

The patch also corrects a reference to a documentation file while
I was at it.

Note from Mathieu: the documentation reference change should have been
done in a separate patch, but I guess no one will really care.
Signed-off-by: default avatarJesper Juhl <jesper.juhl@gmail.com>
Acked-by: default avatar"David J. Wilder" <wilder@us.ibm.com>
Tested-by: default avatar"David J. Wilder" <wilder@us.ibm.com>
Signed-off-by: default avatarMathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Tom Zanussi <zanussi@us.ibm.com>
Cc: Karim Yaghmour <karim@opersys.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent e804a4a4
/* /*
* Public API and common code for kernel->userspace relay file support. * Public API and common code for kernel->userspace relay file support.
* *
* See Documentation/filesystems/relayfs.txt for an overview of relayfs. * See Documentation/filesystems/relay.txt for an overview.
* *
* Copyright (C) 2002-2005 - Tom Zanussi (zanussi@us.ibm.com), IBM Corp * Copyright (C) 2002-2005 - Tom Zanussi (zanussi@us.ibm.com), IBM Corp
* Copyright (C) 1999-2005 - Karim Yaghmour (karim@opersys.com) * Copyright (C) 1999-2005 - Karim Yaghmour (karim@opersys.com)
...@@ -426,6 +426,7 @@ static struct rchan_buf *relay_open_buf(struct rchan *chan, unsigned int cpu) ...@@ -426,6 +426,7 @@ static struct rchan_buf *relay_open_buf(struct rchan *chan, unsigned int cpu)
free_buf: free_buf:
relay_destroy_buf(buf); relay_destroy_buf(buf);
buf = NULL;
free_name: free_name:
kfree(tmpname); kfree(tmpname);
end: end:
......
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