Skip to contentSkip to conversation

printk: fix discarding message when recursion_bug

PATCH In review Hiroshi Shimamoto 2 participants 4 messages Dec 19, 2008

lore
Share & tools
lore

Hiroshi Shimamoto

author
#0 lore raw

PATCH 1/1 printk: fix discarding message when recursion_bug

From: Hiroshi Shimamoto <[email protected]>

Impact: fix

When recursion_bug is true, kernel discards original message because printk_buf contains recursion_bug_msg with NULL terminator. The sizeof(recursion_bug_msg) makes this, use strlen() to get correct length without NULL terminator.

Reported-by Toshikazu Nakayama <[email protected]>
Signed-off-by Hiroshi Shimamoto <[email protected]>
---
 kernel/printk.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
kernel/printk.c +1 -1
index f492f15..e651ab0 100644
@@ -662,7 +662,7 @@ asmlinkage int vprintk(const char *fmt, va_list args)
 	if (recursion_bug) {
 		recursion_bug = 0;
 		strcpy(printk_buf, recursion_bug_msg);
-		printed_len = sizeof(recursion_bug_msg);
+		printed_len = strlen(recursion_bug_msg);
 	}
 	/* Emit the output into the temporary buffer */
 	printed_len += vscnprintf(printk_buf + printed_len,
Signature · 1 line
1.6.0.4
#1 lore raw
Quoted 8 lines · Hiroshi Shimamoto

From: Hiroshi Shimamoto <[email protected]>

Impact: fix

When recursion_bug is true, kernel discards original message because printk_buf contains recursion_bug_msg with NULL terminator. The sizeof(recursion_bug_msg) makes this, use strlen() to get correct length without NULL terminator.

Quoted 5 lines
Reported-by Toshikazu Nakayama <[email protected]>
Signed-off-by Hiroshi Shimamoto <[email protected]>
---
 kernel/printk.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

Good one - applied to tip/core/printk, thanks!

Btw., i'm curious: in what situation was such recursion observed, and how did the kernel behave? You saw a truncated recursion message in dmesg - or was it worse?

Ingo

author
#2 lore raw
Quoted 16 lines · Ingo Molnar
Quoted 8 lines · Hiroshi Shimamoto

From: Hiroshi Shimamoto <[email protected]>

Impact: fix

When recursion_bug is true, kernel discards original message because printk_buf contains recursion_bug_msg with NULL terminator. The sizeof(recursion_bug_msg) makes this, use strlen() to get correct length without NULL terminator.

Quoted 5 lines
Reported-by Toshikazu Nakayama <[email protected]>
Signed-off-by Hiroshi Shimamoto <[email protected]>
---
 kernel/printk.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
Quoted 5 lines

Good one - applied to tip/core/printk, thanks!

Btw., i'm curious: in what situation was such recursion observed, and how did the kernel behave? You saw a truncated recursion message in dmesg - or was it worse?

I'm not sure about the real situation. I've heard this issue was found in printing messages in NMI handler, maybe with artificial kernel stuck.

Thanks,
Hiroshi

#3 lore raw
Quoted 17 lines · Hiroshi Shimamoto
Quoted 16 lines · Ingo Molnar
Quoted 13 lines · Hiroshi Shimamoto

From: Hiroshi Shimamoto <[email protected]>

Impact: fix

When recursion_bug is true, kernel discards original message because printk_buf contains recursion_bug_msg with NULL terminator. The sizeof(recursion_bug_msg) makes this, use strlen() to get correct length without NULL terminator.

Reported-by Toshikazu Nakayama <[email protected]>
Signed-off-by Hiroshi Shimamoto <[email protected]>
---
 kernel/printk.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
Quoted 8 lines
Quoted 5 lines

Good one - applied to tip/core/printk, thanks!

Btw., i'm curious: in what situation was such recursion observed, and how did the kernel behave? You saw a truncated recursion message in dmesg - or was it worse?

I'm not sure about the real situation. I've heard this issue was found in printing messages in NMI handler, maybe with artificial kernel stuck.

yeah, accidental NMI recursion back into printk could indeed cause the recursion message to pop up.

Ingo