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22c1657d05
Use fstat() only to pre-allocate a big enough buffer.
This fixes a race where if the file grows between fstat() and read()
we would be missing the end of the file, and if the file slims down
read() would just fail.
Fixes: 316964709e "util: add os_read_file() helper"
Reported-by: Jason Ekstrand <jason@jlekstrand.net>
Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
107 lines
1.9 KiB
C
107 lines
1.9 KiB
C
/*
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* Copyright 2019 Intel Corporation
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* SPDX-License-Identifier: MIT
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*/
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#include "os_file.h"
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#include <errno.h>
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#include <stdlib.h>
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#if defined(__linux__)
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#include <fcntl.h>
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#include <sys/stat.h>
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#include <unistd.h>
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static ssize_t
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readN(int fd, char *buf, size_t len)
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{
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int err = -ENODATA;
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size_t total = 0;
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do {
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ssize_t ret = read(fd, buf + total, len - total);
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if (ret < 0)
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ret = -errno;
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if (ret == -EINTR || ret == -EAGAIN)
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continue;
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if (ret <= 0)
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break;
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total += ret;
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} while (total != len);
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return total ? total : err;
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}
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char *
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os_read_file(const char *filename)
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{
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/* Note that this also serves as a slight margin to avoid a 2x grow when
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* the file is just a few bytes larger when we read it than when we
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* fstat'ed it.
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* The string's NULL terminator is also included in here.
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*/
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size_t len = 64;
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int fd = open(filename, O_RDONLY);
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if (fd == -1) {
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/* errno set by open() */
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return NULL;
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}
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/* Pre-allocate a buffer at least the size of the file if we can read
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* that information.
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*/
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struct stat stat;
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if (fstat(fd, &stat) == 0)
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len += stat.st_size;
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char *buf = malloc(len);
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if (!buf) {
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close(fd);
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errno = -ENOMEM;
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return NULL;
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}
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ssize_t read;
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size_t offset = 0, remaining = len - 1;
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while ((read = readN(fd, buf + offset, remaining)) == remaining) {
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char *newbuf = realloc(buf, 2 * len);
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if (!newbuf) {
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free(buf);
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close(fd);
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errno = -ENOMEM;
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return NULL;
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}
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buf = newbuf;
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len *= 2;
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offset += read;
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remaining = len - offset - 1;
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}
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close(fd);
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if (read > 0)
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offset += read;
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buf[offset] = '\0';
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return buf;
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}
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#else
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char *
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os_read_file(const char *filename)
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{
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errno = -ENOSYS;
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return NULL;
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}
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#endif
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