Commit dcc4e572 authored by Kees Cook's avatar Kees Cook Committed by Steven Rostedt (Google)
Browse files

seq_buf: Introduce DECLARE_SEQ_BUF and seq_buf_str() 

Solve two ergonomic issues with struct seq_buf;

1) Too much boilerplate is required to initialize:

	struct seq_buf s;
	char buf[32];

	seq_buf_init(s, buf, sizeof(buf));

Instead, we can build this directly on the stack. Provide
DECLARE_SEQ_BUF() macro to do this:

	DECLARE_SEQ_BUF(s, 32);

2) %NUL termination is fragile and requires 2 steps to get a valid
   C String (and is a layering violation exposing the "internals" of
   seq_buf):

	seq_buf_terminate(s);
	do_something(s->buffer);

Instead, we can just return s->buffer directly after terminating it in
the refactored seq_buf_terminate(), now known as seq_buf_str():

	do_something(seq_buf_str(s));

Link: https://lore.kernel.org/linux-trace-kernel/20231027155634.make.260-kees@kernel.org
Link: https://lore.kernel.org/linux-trace-kernel/20231026194033.it.702-kees@kernel.org/



Cc: Yosry Ahmed <yosryahmed@google.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Justin Stitt <justinstitt@google.com>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Yun Zhou <yun.zhou@windriver.com>
Cc: Jacob Keller <jacob.e.keller@intel.com>
Cc: Zhen Lei <thunder.leizhen@huawei.com>
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent 29e06c10

include/linux/seq_buf.h

+17 −4
Original line number Diff line number Diff line
@@ -21,9 +21,18 @@ struct seq_buf { 
	size_t			len;

};



#define DECLARE_SEQ_BUF(NAME, SIZE)			\

	char __ ## NAME ## _buffer[SIZE] = "";		\

	struct seq_buf NAME = {				\

		.buffer = &__ ## NAME ## _buffer,	\

		.size = SIZE,				\

	}



static inline void seq_buf_clear(struct seq_buf *s)

{

	s->len = 0;

	if (s->size)

		s->buffer[0] = '\0';

}



static inline void
@@ -69,8 +78,8 @@ static inline unsigned int seq_buf_used(struct seq_buf *s) 
}



/**

 * seq_buf_terminate - Make sure buffer is nul terminated

 * @s: the seq_buf descriptor to terminate.

 * seq_buf_str - get %NUL-terminated C string from seq_buf

 * @s: the seq_buf handle

 *

 * This makes sure that the buffer in @s is nul terminated and

 * safe to read as a string.
@@ -81,16 +90,20 @@ static inline unsigned int seq_buf_used(struct seq_buf *s) 
 *

 * After this function is called, s->buffer is safe to use

 * in string operations.

 *

 * Returns @s->buf after making sure it is terminated.

 */

static inline void seq_buf_terminate(struct seq_buf *s)

static inline const char *seq_buf_str(struct seq_buf *s)

{

	if (WARN_ON(s->size == 0))

		return;

		return "";



	if (seq_buf_buffer_left(s))

		s->buffer[s->len] = 0;

	else

		s->buffer[s->size - 1] = 0;



	return s->buffer;

}



/**

kernel/trace/trace.c

+1 −10
Original line number Diff line number Diff line
@@ -3828,15 +3828,6 @@ static bool trace_safe_str(struct trace_iterator *iter, const char *str, 
	return false;

}



static const char *show_buffer(struct trace_seq *s)

{

	struct seq_buf *seq = &s->seq;



	seq_buf_terminate(seq);



	return seq->buffer;

}



static DEFINE_STATIC_KEY_FALSE(trace_no_verify);



static int test_can_verify_check(const char *fmt, ...)
@@ -3976,7 +3967,7 @@ void trace_check_vprintf(struct trace_iterator *iter, const char *fmt, 
		 */

		if (WARN_ONCE(!trace_safe_str(iter, str, star, len),

			      "fmt: '%s' current_buffer: '%s'",

			      fmt, show_buffer(&iter->seq))) {

			      fmt, seq_buf_str(&iter->seq.seq))) {

			int ret;



			/* Try to safely read the string */

lib/seq_buf.c

+1 −3
Original line number Diff line number Diff line
@@ -109,9 +109,7 @@ void seq_buf_do_printk(struct seq_buf *s, const char *lvl) 
	if (s->size == 0 || s->len == 0)

		return;



	seq_buf_terminate(s);



	start = s->buffer;

	start = seq_buf_str(s);

	while ((lf = strchr(start, '\n'))) {

		int len = lf - start + 1;