Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [PATCH 3.16 271/357] kernel/printk/printk.c: fix faulty logic in the case of recursive printk | Date | Fri, 3 Oct 2014 14:30:57 -0700 |
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3.16-stable review patch. If anyone has any objections, please let me know.
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From: Patrick Palka <patrick@parcs.ath.cx>
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@parcs.ath.cx> Reviewed-by: Petr Mladek <pmladek@suse.cz> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- 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)); } /*
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