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feat(skipcpio): speed up and harden skipcpio 

Before:
```
Benchmark #1: ./skipcpio/skipcpio test-5.10.15-200.fc33.x86_64.img >/dev/null
  Time (mean ± σ):     125.5 ms ±   0.9 ms    [User: 97.4 ms, System: 27.9 ms]
  Range (min … max):   124.8 ms … 129.4 ms    23 runs
```

After:
```
Benchmark #1: ./skipcpio/skipcpio test-5.10.15-200.fc33.x86_64.img >/dev/null
  Time (mean ± σ):      12.2 ms ±   0.3 ms    [User: 2.7 ms, System: 9.5 ms]
  Range (min … max):    11.7 ms …  13.6 ms    212 runs
```

Besides the speedup, skipcpio now parses the cpio header and is not
falsely ending when the early cpio payload contains `TRAILER!!!`.

Fixes: https://github.com/dracutdevs/dracut/issues/1123
master
Harald Hoyer 2021-02-24 13:55:54 +01:00 committed by Harald Hoyer
parent c67b624637
commit 630334950c
1 changed files with 75 additions and 26 deletions
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101
skipcpio/skipcpio.c
View File

@ -23,16 +23,46 @@
#define _GNU_SOURCE
#endif

#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

#define CPIO_MAGIC "070701"
#define CPIO_END "TRAILER!!!"
#define CPIO_ENDLEN (sizeof(CPIO_END)-1)
#define CPIO_ENDLEN (sizeof(CPIO_END) - 1)

static char buf[CPIO_ENDLEN * 2 + 1];
#define CPIO_ALIGNMENT 4

struct cpio_header {
char c_magic[6];
char c_ino[8];
char c_mode[8];
char c_uid[8];
char c_gid[8];
char c_nlink[8];
char c_mtime[8];
char c_filesize[8];
char c_dev_maj[8];
char c_dev_min[8];
char c_rdev_maj[8];
char c_rdev_min[8];
char c_namesize[8];
char c_chksum[8];
} __attribute__((packed));

struct buf_struct {
struct cpio_header h;
char filename[CPIO_ENDLEN];
} __attribute__((packed));

union buf_union {
struct buf_struct cpio;
char copy_buffer[2048];
};

static union buf_union buf;

#define ALIGN_UP(n, a) (((n) + (a) - 1) & (~((a) - 1)))

int main(int argc, char **argv)
{
@ -51,7 +81,7 @@ int main(int argc, char **argv)
exit(1);
}

s = fread(buf, 6, 1, f);
s = fread(&buf.cpio, sizeof(buf.cpio), 1, f);
if (s <= 0) {
fprintf(stderr, "Read error from file '%s'\n", argv[1]);
fclose(f);
@ -60,25 +90,44 @@ int main(int argc, char **argv)
fseek(f, 0, SEEK_SET);

/* check, if this is a cpio archive */
if (buf[0] == '0' && buf[1] == '7' && buf[2] == '0' && buf[3] == '7' && buf[4] == '0' && buf[5] == '1') {
if (memcmp(buf.cpio.h.c_magic, CPIO_MAGIC, 6) == 0) {

long pos = 0;

/* Search for CPIO_END */
do {
char *h;
fseek(f, pos, SEEK_SET);
buf[sizeof(buf) - 1] = 0;
s = fread(buf, CPIO_ENDLEN, 2, f);
if (s <= 0)
break;
unsigned long filesize;
unsigned long filename_length;

h = memmem(buf, sizeof(buf), CPIO_END, sizeof(CPIO_END));
if (h) {
pos = (h - buf) + pos + CPIO_ENDLEN;
do {
// zero string, spilling into next unused field, to use strtol
buf.cpio.h.c_chksum[0] = 0;
filename_length = strtoul(buf.cpio.h.c_namesize, NULL, 16);
pos = ALIGN_UP(pos + sizeof(struct cpio_header) + filename_length, CPIO_ALIGNMENT);

// zero string, spilling into next unused field, to use strtol
buf.cpio.h.c_dev_maj[0] = 0;
filesize = strtoul(buf.cpio.h.c_filesize, NULL, 16);
pos = ALIGN_UP(pos + filesize, CPIO_ALIGNMENT);

if (filename_length == (CPIO_ENDLEN + 1)
&& strncmp(buf.cpio.filename, CPIO_END, CPIO_ENDLEN) == 0) {
fseek(f, pos, SEEK_SET);
break;
}
pos += CPIO_ENDLEN;

if (fseek(f, pos, SEEK_SET) != 0) {
perror("fseek");
exit(1);
}

if (fread(&buf.cpio, sizeof(buf.cpio), 1, f) != 1) {
perror("fread");
exit(1);
}

if (memcmp(buf.cpio.h.c_magic, CPIO_MAGIC, 6) != 0) {
fprintf(stderr, "Corrupt CPIO archive!\n");
exit(1);
}
} while (!feof(f));

if (feof(f)) {
@ -86,33 +135,33 @@ int main(int argc, char **argv)
fseek(f, 0, SEEK_SET);
} else {
/* skip zeros */
while (!feof(f)) {
do {
size_t i;

buf[sizeof(buf) - 1] = 0;
s = fread(buf, 1, sizeof(buf) - 1, f);
s = fread(buf.copy_buffer, 1, sizeof(buf.copy_buffer) - 1, f);
if (s <= 0)
break;

for (i = 0; (i < s) && (buf[i] == 0); i++) ;
for (i = 0; (i < s) && (buf.copy_buffer[i] == 0); i++) ;

if (buf[i] != 0) {
if (buf.copy_buffer[i] != 0) {
pos += i;

fseek(f, pos, SEEK_SET);
break;
}

pos += s;
}
} while (!feof(f));
}
}
/* cat out the rest */
while (!feof(f)) {
s = fread(buf, 1, sizeof(buf), f);
s = fread(buf.copy_buffer, 1, sizeof(buf.copy_buffer), f);
if (s <= 0)
break;

s = fwrite(buf, 1, s, stdout);
s = fwrite(buf.copy_buffer, 1, s, stdout);
if (s <= 0)
break;
}