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authorTejun Heo <tj@kernel.org>2015-06-26 01:01:24 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2015-06-26 03:00:38 +0300
commitd43ff430f434d862db59582c0f1f02382a678036 (patch)
tree1ade66d9cce26fc358a3d814bec1ad7bb06ec8cc /kernel
parent4ae555a5313a302d36e34b3273545e4088c37cce (diff)
downloadlinux-d43ff430f434d862db59582c0f1f02382a678036.tar.xz
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 (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>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/printk/printk.c34
1 files changed, 22 insertions, 12 deletions
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index c099b082cd02..a11549034e07 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;