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Subject[PATCH 01/16] printk: guard the amount written per line by devkmsg_read()
Date
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: Kay Sievers <kay@vrfy.org>
Cc: Petr Mladek <pmladek@suse.cz>
---
include/linux/printk.h | 2 ++
kernel/printk/printk.c | 35 +++++++++++++++++++++++------------
2 files changed, 25 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 879edfc..b6e24af 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -512,7 +512,7 @@ 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)
@@ -565,11 +565,18 @@ static ssize_t devkmsg_write(struct kiocb *iocb, struct iov_iter *from)
return ret;
}

+static void append_char(char **pp, char *e, char c)
+{
+ if (*pp < e)
+ *(*pp)++ = c;
+}
+
static ssize_t devkmsg_read(struct file *file, char __user *buf,
size_t count, loff_t *ppos)
{
struct devkmsg_user *user = file->private_data;
struct printk_log *msg;
+ char *p, *e;
u64 ts_usec;
size_t i;
char cont = '-';
@@ -579,6 +586,9 @@ 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 +635,9 @@ 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 +645,11 @@ 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 +658,31 @@ 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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