path: root/main/musl/3002-stdio-implement-fopencookie-3.patch

From f501fa8271c7464c9c75762d2c9f43e494e416d8 Mon Sep 17 00:00:00 2001
From: William Pitcock <nenolod@dereferenced.org>
Date: Sun, 24 Sep 2017 16:37:48 -0500
Subject: [PATCH] stdio: implement fopencookie(3)

The fopencookie(3) function allows the programmer to create a custom
stdio implementation, using four hook functions which operate on a
"cookie" data type.

Changelog:

v9:
- make read function more robust, should have been in v8 but i forgot to commit

v8:
- fix possible ungetc() underflow
- style cleanups

v7:
- include GNU typedefs for cookie i/o functions

v6:
- remove pointer arithmetic instead using a structure to contain the parent FILE
  object
- set F_ERR flag where appropriate
- style fixes
- fix stdio readahead to handle single-byte read case (as pointed out by dalias,
  tested by custom fuzzer)
- handle seek return values correctly (found by fuzzing)

v5:
- implement stdio readahead buffering support

v4:
- remove parameter names from header function declarations

v3:
- remove spurious `struct winsize`
- make f->lock unconditionally 0

v2:
- properly implement stdio buffering

v1:
- initial proof of concept
---
 include/stdio.h         |  14 +++++
 src/stdio/fopencookie.c | 138 ++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 152 insertions(+)
 create mode 100644 src/stdio/fopencookie.c

diff --git a/include/stdio.h b/include/stdio.h
index 884d2e6a..2932c76f 100644
--- a/include/stdio.h
+++ b/include/stdio.h
@@ -182,6 +182,20 @@ int vasprintf(char **, const char *, __isoc_va_list);
 #ifdef _GNU_SOURCE
 char *fgets_unlocked(char *, int, FILE *);
 int fputs_unlocked(const char *, FILE *);
+
+typedef ssize_t (cookie_read_function_t)(void *, char *, size_t);
+typedef ssize_t (cookie_write_function_t)(void *, const char *, size_t);
+typedef int (cookie_seek_function_t)(void *, off_t *, int);
+typedef int (cookie_close_function_t)(void *);
+
+typedef struct {
+	cookie_read_function_t *read;
+	cookie_write_function_t *write;
+	cookie_seek_function_t *seek;
+	cookie_close_function_t *close;
+} cookie_io_functions_t;
+
+FILE *fopencookie(void *, const char *, cookie_io_functions_t);
 #endif
 
 #if defined(_LARGEFILE64_SOURCE) || defined(_GNU_SOURCE)
diff --git a/src/stdio/fopencookie.c b/src/stdio/fopencookie.c
new file mode 100644
index 00000000..2f46dd53
--- /dev/null
+++ b/src/stdio/fopencookie.c
@@ -0,0 +1,138 @@
+#define _GNU_SOURCE
+#include "stdio_impl.h"
+#include <stdlib.h>
+#include <sys/ioctl.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <string.h>
+
+struct fcookie {
+	void *cookie;
+	cookie_io_functions_t iofuncs;
+};
+
+struct cookie_FILE {
+	FILE f;
+	struct fcookie fc;
+	unsigned char buf[UNGET+BUFSIZ];
+};
+
+static size_t cookieread(FILE *f, unsigned char *buf, size_t len)
+{
+	struct fcookie *fc = f->cookie;
+	ssize_t ret = -1;
+	size_t remain = len, readlen = 0;
+	size_t len2 = len - !!f->buf_size;
+
+	if (!fc->iofuncs.read) goto bail;
+
+	if (len2) {
+		ret = fc->iofuncs.read(fc->cookie, (char *) buf, len2);
+		if (ret <= 0) goto bail;
+
+		readlen += ret;
+		remain -= ret;
+	}
+
+	if (!f->buf_size || remain > !!f->buf_size) return readlen;
+
+	f->rpos = f->buf;
+	ret = fc->iofuncs.read(fc->cookie, (char *) f->rpos, f->buf_size);
+	if (ret <= 0) goto bail;
+	f->rend = f->rpos + ret;
+
+	buf[readlen++] = *f->rpos++;
+
+	return readlen;
+
+bail:
+	f->flags |= ret == 0 ? F_EOF : F_ERR;
+	f->rpos = f->rend = f->buf;
+	return readlen;
+}
+
+static size_t cookiewrite(FILE *f, const unsigned char *buf, size_t len)
+{
+	struct fcookie *fc = f->cookie;
+	ssize_t ret;
+	size_t len2 = f->wpos - f->wbase;
+	if (!fc->iofuncs.write) return len;
+	if (len2) {
+		f->wpos = f->wbase;
+		if (cookiewrite(f, f->wpos, len2) < len2) return 0;
+	}
+	ret = fc->iofuncs.write(fc->cookie, (const char *) buf, len);
+	if (ret < 0) {
+		f->wpos = f->wbase = f->wend = 0;
+		f->flags |= F_ERR;
+		return 0;
+	}
+	return ret;
+}
+
+static off_t cookieseek(FILE *f, off_t off, int whence)
+{
+	struct fcookie *fc = f->cookie;
+	int res;
+	if (whence > 2U) {
+		errno = EINVAL;
+		return -1;
+	}
+	if (!fc->iofuncs.seek) {
+		errno = ENOTSUP;
+		return -1;
+	}
+	res = fc->iofuncs.seek(fc->cookie, &off, whence);
+	if (res < 0)
+		return res;
+	return off;
+}
+
+static int cookieclose(FILE *f)
+{
+	struct fcookie *fc = f->cookie;
+	if (fc->iofuncs.close) return fc->iofuncs.close(fc->cookie);
+	return 0;
+}
+
+FILE *fopencookie(void *cookie, const char *mode, cookie_io_functions_t iofuncs)
+{
+	struct cookie_FILE *f;
+
+	/* Check for valid initial mode character */
+	if (!strchr("rwa", *mode)) {
+		errno = EINVAL;
+		return 0;
+	}
+
+	/* Allocate FILE+fcookie+buffer or fail */
+	if (!(f=malloc(sizeof *f))) return 0;
+
+	/* Zero-fill only the struct, not the buffer */
+	memset(&f->f, 0, sizeof f->f);
+
+	/* Impose mode restrictions */
+	if (!strchr(mode, '+')) f->f.flags = (*mode == 'r') ? F_NOWR : F_NORD;
+
+	/* Set up our fcookie */
+	f->fc.cookie = cookie;
+	f->fc.iofuncs.read = iofuncs.read;
+	f->fc.iofuncs.write = iofuncs.write;
+	f->fc.iofuncs.seek = iofuncs.seek;
+	f->fc.iofuncs.close = iofuncs.close;
+
+	f->f.fd = -1;
+	f->f.cookie = &f->fc;
+	f->f.buf = f->buf + UNGET;
+	f->f.buf_size = BUFSIZ;
+	f->f.lbf = EOF;
+
+	/* Initialize op ptrs. No problem if some are unneeded. */
+	f->f.read = cookieread;
+	f->f.write = cookiewrite;
+	f->f.seek = cookieseek;
+	f->f.close = cookieclose;
+
+	/* Add new FILE to open file list */
+	return __ofl_add(&f->f);
+}
-- 
2.15.0