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Message-Id: <20171012000520.16806-1-nenolod@dereferenced.org>
Date: Thu, 12 Oct 2017 00:05:20 +0000
From: William Pitcock <nenolod@...eferenced.org>
To: musl@...ts.openwall.com
Cc: William Pitcock <nenolod@...eferenced.org>
Subject: [PATCH v6] 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:
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 | 9 ++++
src/stdio/fopencookie.c | 141 ++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 150 insertions(+)
create mode 100644 src/stdio/fopencookie.c
diff --git a/include/stdio.h b/include/stdio.h
index 884d2e6a..da0563f6 100644
--- a/include/stdio.h
+++ b/include/stdio.h
@@ -182,6 +182,15 @@ int vasprintf(char **, const char *, __isoc_va_list);
#ifdef _GNU_SOURCE
char *fgets_unlocked(char *, int, FILE *);
int fputs_unlocked(const char *, FILE *);
+
+typedef struct {
+ ssize_t (*read)(void *, char *, size_t);
+ ssize_t (*write)(void *, const char *, size_t);
+ int (*seek)(void *, off_t *, int);
+ int (*close)(void *);
+} 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..bcf42c10
--- /dev/null
+++ b/src/stdio/fopencookie.c
@@ -0,0 +1,141 @@
+#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;
+
+ if (!fc->iofuncs.read) goto bail;
+
+ ret = fc->iofuncs.read(fc->cookie, (char *) buf, len > 1 ? (len - 1) : 1);
+ if (ret <= 0) goto bail;
+
+ readlen += ret;
+ remain -= ret;
+
+ 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;
+
+ if (remain > 0) {
+ if (remain > f->buf_size) remain = f->buf_size;
+ memcpy(buf + readlen, f->rpos, remain);
+ readlen += remain;
+ f->rpos += remain;
+ }
+
+ return readlen;
+
+bail:
+ f->flags |= F_EOF ^ ((F_ERR^F_EOF) & ret);
+ 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 > 2) {
+ 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, 0, sizeof(FILE));
+
+ /* 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;
+ f->f.buf_size = BUFSIZ;
+ f->f.lbf = EOF;
+
+ /* enable opportunistic stdio locking */
+ f->f.lock = 0;
+
+ /* 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);
+}
--
2.13.3
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