From 0048f176788f3c5bd3348244f6e2a1a3ad9b733b Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Thu, 14 May 2015 11:36:36 -0400 Subject: [PATCH] printk: guard the amount written per line by devkmsg_read() This patchset updates netconsole so that it can emit messages with the same header as used in /dev/kmsg which gives neconsole receiver full log information which enables things like structured logging and detection of lost messages. This patch: devkmsg_read() uses 8k buffer and assumes that the formatted output message won't overrun which seems safe given LOG_LINE_MAX, the current use of dict and the escaping method being used; however, we're planning to use devkmsg formatting wider and accounting for the buffer size properly isn't that complicated. This patch defines CONSOLE_EXT_LOG_MAX as 8192 and updates devkmsg_read() so that it limits output accordingly. Signed-off-by: Tejun Heo Cc: David Miller Cc: Kay Sievers Reviewed-by: Petr Mladek Cc: Tetsuo Handa Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Change-Id: Idead54c1fb93161aebd0e00be0b66f96b907233b --- include/linux/printk.h | 4 ++++ kernel/printk_kmsg.c | 34 ++++++++++++++++++++++------------ 2 files changed, 26 insertions(+), 12 deletions(-) diff --git a/include/linux/printk.h b/include/linux/printk.h index 708b8a8..db9831e 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -33,6 +33,10 @@ static inline const char *printk_skip_level(const char *buffer) return buffer; } +#ifdef CONFIG_MULTIPLE_KMSG +#define CONSOLE_EXT_LOG_MAX 8192 +#endif + extern int console_printk[]; #define console_loglevel (console_printk[0]) diff --git a/kernel/printk_kmsg.c b/kernel/printk_kmsg.c index 7480558..c7023f7 100644 --- a/kernel/printk_kmsg.c +++ b/kernel/printk_kmsg.c @@ -487,6 +487,11 @@ static int check_syslog_permissions(int type, bool from_file) return security_syslog(type); } +static void append_char(char **pp, char *e, char c) +{ + if (*pp < e) + *(*pp)++ = c; +} /* /dev/kmsg - userspace message inject/listen interface */ struct devkmsg_user { @@ -494,7 +499,7 @@ struct devkmsg_user { u32 idx; enum log_flags prev; struct mutex lock; - char buf[8192]; + char buf[CONSOLE_EXT_LOG_MAX]; }; static ssize_t devkmsg_writev(struct kiocb *iocb, const struct iovec *iv, @@ -558,6 +563,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf, { struct devkmsg_user *user = file->private_data; struct log *msg; + char *p, *e; u64 ts_usec; size_t i; char cont = '-'; @@ -567,6 +573,9 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf, if (!user) return -EBADF; + p = user->buf; + e = user->buf + sizeof(user->buf); + ret = mutex_lock_interruptible(&user->lock); if (ret) return ret; @@ -613,9 +622,9 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf, ((user->prev & LOG_CONT) && !(msg->flags & LOG_PREFIX))) cont = '+'; - len = sprintf(user->buf, "%u,%llu,%llu,%c;", - (msg->facility << 3) | msg->level, - user->seq, ts_usec, cont); + p += scnprintf(p, e - p, "%u,%llu,%llu,%c;", + (msg->facility << 3) | msg->level, + user->seq, ts_usec, cont); user->prev = msg->flags; /* escape non-printable characters */ @@ -623,11 +632,11 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf, unsigned char c = log_text(msg)[i]; if (c < ' ' || c >= 127 || c == '\\') - len += sprintf(user->buf + len, "\\x%02x", c); + p += scnprintf(p, e - p, "\\x%02x", c); else - user->buf[len++] = c; + append_char(&p, e, c); } - user->buf[len++] = '\n'; + append_char(&p, e, '\n'); if (msg->dict_len) { bool line = true; @@ -636,30 +645,31 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf, unsigned char c = log_dict(msg)[i]; if (line) { - user->buf[len++] = ' '; + append_char(&p, e, ' '); line = false; } if (c == '\0') { - user->buf[len++] = '\n'; + append_char(&p, e, '\n'); line = true; continue; } if (c < ' ' || c >= 127 || c == '\\') { - len += sprintf(user->buf + len, "\\x%02x", c); + p += scnprintf(p, e - p, "\\x%02x", c); continue; } - user->buf[len++] = c; + append_char(&p, e, c); } - user->buf[len++] = '\n'; + append_char(&p, e, '\n'); } user->idx = log_next(user->idx); user->seq++; raw_spin_unlock_irq(&logbuf_lock); + len = p - user->buf; if (len > count) { ret = -EINVAL; goto out; -- 2.7.4