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authorPetr Mladek <pmladek@suse.com>2016-12-12 16:45:40 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2016-12-12 18:55:09 -0800
commit4a998e322abc935e95efc1a8108e6102be636a43 (patch)
tree41db744c25a5864076d74d3a929cd4c5ecfc9b5e
parent8e8780a547d987b6465c9458402177fe706c5624 (diff)
downloadlinux-4a998e322abc935e95efc1a8108e6102be636a43.tar.bz2
printk/NMI: fix up handling of the full nmi log buffer
vsnprintf() adds the trailing '\0' but it does not count it into the number of printed characters. The result is that there is one byte less space for the real characters in the buffer. The broken check for the free space might cause that we will repeatedly try to print 1 character into the buffer, never reach the full buffer, and do not count the messages as missed. Also vsnprintf() returns the number of characters that would be printed if the buffer was big enough. As a result, s->len might be bigger than the size of the buffer[*]. And the printk() function might return bigger len than it really printed. Both problems are fixed by using vscnprintf() instead. Note that I though about increasing the number of missed messages even when the message was shrunken. But it made the code even more complicated. I think that it is not worth it. Shrunken messages are usually easy to recognize. And it should be a corner case. [*] The overflown s->len value is crazy and unexpected. I "made a mistake" and reported this situation as an internal error when fixed handling of PR_CONT headers in some other patch. Link: http://lkml.kernel.org/r/20161208174912.GA17042@linux.suse Signed-off-by: Petr Mladek <pmladek@suse.com> CcL Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> Cc: Chris Mason <clm@fb.com> Cc: David Sterba <dsterba@suse.com> Cc: Jason Wessel <jason.wessel@windriver.com> Cc: Josef Bacik <jbacik@fb.com> Cc: Joe Perches <joe@perches.com> Cc: Jaroslav Kysela <perex@perex.cz> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Takashi Iwai <tiwai@suse.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--kernel/printk/nmi.c5
1 files changed, 3 insertions, 2 deletions
diff --git a/kernel/printk/nmi.c b/kernel/printk/nmi.c
index 16bab471c7e2..152533edc56f 100644
--- a/kernel/printk/nmi.c
+++ b/kernel/printk/nmi.c
@@ -67,7 +67,8 @@ static int vprintk_nmi(const char *fmt, va_list args)
again:
len = atomic_read(&s->len);
- if (len >= sizeof(s->buffer)) {
+ /* The trailing '\0' is not counted into len. */
+ if (len >= sizeof(s->buffer) - 1) {
atomic_inc(&nmi_message_lost);
return 0;
}
@@ -79,7 +80,7 @@ again:
if (!len)
smp_rmb();
- add = vsnprintf(s->buffer + len, sizeof(s->buffer) - len, fmt, args);
+ add = vscnprintf(s->buffer + len, sizeof(s->buffer) - len, fmt, args);
/*
* Do it once again if the buffer has been flushed in the meantime.