From 1538399c3e28ab77dee17bf1ccc8391b314373f6 Mon Sep 17 00:00:00 2001 From: Patrick Palka Date: Tue, 9 Sep 2014 14:50:48 -0700 Subject: [PATCH] kernel/printk/printk.c: fix faulty logic in the case of recursive printk 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 bfe6782194f4 ("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: bfe6782194f4c92f ("printk: remove separate printk_sched buffers and use printk buf instead") Signed-off-by: Patrick Palka Reviewed-by: Petr Mladek Reviewed-by: Jan Kara Acked-by: Steven Rostedt Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/printk/printk.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index e04c455a0e386..1ce770687ea83 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -1665,15 +1665,15 @@ asmlinkage int vprintk_emit(int facility, int level, 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)); } /* -- 2.39.5