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Message-Id: <20231026194033.it.702-kees@kernel.org>
Date: Thu, 26 Oct 2023 12:40:37 -0700
From: Kees Cook <keescook@...omium.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Kees Cook <keescook@...omium.org>,
"Matthew Wilcox (Oracle)" <willy@...radead.org>,
Christoph Hellwig <hch@....de>,
Justin Stitt <justinstitt@...gle.com>,
Kent Overstreet <kent.overstreet@...ux.dev>,
Petr Mladek <pmladek@...e.com>,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
Rasmus Villemoes <linux@...musvillemoes.dk>,
Sergey Senozhatsky <senozhatsky@...omium.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Arnd Bergmann <arnd@...db.de>,
Jonathan Corbet <corbet@....net>,
Yun Zhou <yun.zhou@...driver.com>,
Jacob Keller <jacob.e.keller@...el.com>,
Zhen Lei <thunder.leizhen@...wei.com>,
linux-trace-kernel@...r.kernel.org,
Yosry Ahmed <yosryahmed@...gle.com>,
linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH v2] 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 direction after terminating it
in refactored seq_buf_terminate(), now known as seq_buf_str():
do_soemthing(seq_buf_str(s));
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc: Christoph Hellwig <hch@....de>
Cc: Justin Stitt <justinstitt@...gle.com>
Cc: Kent Overstreet <kent.overstreet@...ux.dev>
Cc: Petr Mladek <pmladek@...e.com>
Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Rasmus Villemoes <linux@...musvillemoes.dk>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Jonathan Corbet <corbet@....net>
Cc: Yun Zhou <yun.zhou@...driver.com>
Cc: Jacob Keller <jacob.e.keller@...el.com>
Cc: Zhen Lei <thunder.leizhen@...wei.com>
Cc: linux-trace-kernel@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
v2 - rename seq_buf_cstr() to seq_buf_str() (rostedt)
v1 - https://lore.kernel.org/all/20231026170722.work.638-kees@kernel.org/
---
include/linux/seq_buf.h | 19 +++++++++++++++----
kernel/trace/trace.c | 11 +----------
lib/seq_buf.c | 4 +---
3 files changed, 17 insertions(+), 17 deletions(-)
diff --git a/include/linux/seq_buf.h b/include/linux/seq_buf.h
index 8483e4b2d0d2..71eb4d624308 100644
--- a/include/linux/seq_buf.h
+++ b/include/linux/seq_buf.h
@@ -21,9 +21,16 @@ 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 +76,8 @@ 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 +88,20 @@ 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 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;
}
/**
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index d629065c2383..2539cfc20a97 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -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 */
diff --git a/lib/seq_buf.c b/lib/seq_buf.c
index b7477aefff53..23518f77ea9c 100644
--- a/lib/seq_buf.c
+++ b/lib/seq_buf.c
@@ -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;
--
2.34.1
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