Patch "kernel/printk/printk.c: fix faulty logic in the case of recursive printk" has been added to the 3.16-stable tree

[<gregkh@xxxxxxxxxxxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    kernel/printk/printk.c: fix faulty logic in the case of recursive printk

to the 3.16-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     kernel-printk-printk.c-fix-faulty-logic-in-the-case-of-recursive-printk.patch
and it can be found in the queue-3.16 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From 000a7d66ec30898f46869be01ab8205b056385d0 Mon Sep 17 00:00:00 2001
From: Patrick Palka <patrick@xxxxxxxxxxxx>
Date: Tue, 9 Sep 2014 14:50:48 -0700
Subject: kernel/printk/printk.c: fix faulty logic in the case of recursive printk

From: Patrick Palka <patrick@xxxxxxxxxxxx>

commit 000a7d66ec30898f46869be01ab8205b056385d0 upstream.

We shouldn't set text_len in the code path that detects printk recursion
because text_len corresponds to the length of the string inside textbuf.
A few lines down from the line

    text_len = strlen(recursion_msg);

is the line

    text_len += vscnprintf(text + text_len, ...);

So if printk detects recursion, it sets text_len to 29 (the length of
recursion_msg) and logs an error.  Then the message supplied by the
caller of printk is stored inside textbuf but offset by 29 bytes.  This
means that the output of the recursive call to printk will contain 29
bytes of garbage in front of it.

This defect is caused by commit 458df9fd4815 ("printk: remove separate
printk_sched buffers and use printk buf instead") which turned the line

    text_len = vscnprintf(text, ...);

into

    text_len += vscnprintf(text + text_len, ...);

To fix this, this patch avoids setting text_len when logging the printk
recursion error.  This patch also marks unlikely() the branch leading up
to this code.

Fixes: 458df9fd4815b478 ("printk: remove separate printk_sched buffers and use printk buf instead")
Signed-off-by: Patrick Palka <patrick@xxxxxxxxxxxx>
Reviewed-by: Petr Mladek <pmladek@xxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
Acked-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 kernel/printk/printk.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1617,15 +1617,15 @@ asmlinkage int vprintk_emit(int facility
 	raw_spin_lock(&logbuf_lock);
 	logbuf_cpu = this_cpu;
 
-	if (recursion_bug) {
+	if (unlikely(recursion_bug)) {
 		static const char recursion_msg[] =
 			"BUG: recent printk recursion!";
 
 		recursion_bug = 0;
-		text_len = strlen(recursion_msg);
 		/* emit KERN_CRIT message */
 		printed_len += log_store(0, 2, LOG_PREFIX|LOG_NEWLINE, 0,
-					 NULL, 0, recursion_msg, text_len);
+					 NULL, 0, recursion_msg,
+					 strlen(recursion_msg));
 	}
 
 	/*


Patches currently in stable-queue which might be from patrick@xxxxxxxxxxxx are

queue-3.16/kernel-printk-printk.c-fix-faulty-logic-in-the-case-of-recursive-printk.patch
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