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printk: guard the amount written per line by devkmsg_read()

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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 (of 7):

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 <tj@kernel.org>
Cc: David Miller <davem@davemloft.net>
Cc: Kay Sievers <kay@vrfy.org>
Reviewed-by: Petr Mladek <pmladek@suse.cz>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Tejun Heo 2015-06-25 15:01:24 -07:00 committed by Linus Torvalds
parent 4ae555a531
commit d43ff430f4
2 changed files with 24 additions and 12 deletions
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2
include/linux/printk.h
View File

@ -30,6 +30,8 @@ static inline const char *printk_skip_level(const char *buffer)
return buffer;
}
#define CONSOLE_EXT_LOG_MAX 8192
/* printk's without a loglevel use this.. */
#define MESSAGE_LOGLEVEL_DEFAULT CONFIG_MESSAGE_LOGLEVEL_DEFAULT

34
kernel/printk/printk.c
View File

@ -505,6 +505,11 @@ 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 {
@ -512,7 +517,7 @@ 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_write(struct kiocb *iocb, struct iov_iter *from)
@ -570,6 +575,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
{
struct devkmsg_user *user = file->private_data;
struct printk_log *msg;
char *p, *e;
u64 ts_usec;
size_t i;
char cont = '-';
@ -579,6 +585,9 @@ 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;
@ -625,9 +634,9 @@ 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 */
@ -635,11 +644,11 @@ 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;
@ -648,30 +657,31 @@ 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;