On Thu 2015-05-14 12:06:20, Tejun Heo wrote:
> 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 <t...@kernel.org>
Reviewed-by: Petr Mladek <pmla...@suse.cz>
It is more secure now.
Best Regards,
Petr
> Cc: Kay Sievers <k...@vrfy.org>
> Cc: Petr Mladek <pmla...@suse.cz>
> ---
> include/linux/printk.h | 2 ++
> kernel/printk/printk.c | 34 ++++++++++++++++++++++------------
> 2 files changed, 24 insertions(+), 12 deletions(-)
>
> diff --git a/include/linux/printk.h b/include/linux/printk.h
> index 9b30871..58b1fec 100644
> --- a/include/linux/printk.h
> +++ b/include/linux/printk.h
> @@ -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
>
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index c099b08..a115490 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -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;
> --
> 2.1.0
>
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