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Unsquashfs: ability to unpack over existing mount points #257

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Unsquashfs: ability to unpack over existing mount points #257

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3 changes: 3 additions & 0 deletions manpages/unsquashfs.1
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Original file line number Diff line number Diff line change
Expand Up @@ -58,6 +58,9 @@ set all file timestamps to TIME, rather than the time stored in the filesystem i
\fB\-cat\fR
cat the files on the command line to stdout.
.TP
\fB\-one\-file\-system\fR
do not cross filesystem boundaries. If a directory is an existing mount point, just skip it.
.TP
\fB\-f\fR, \fB\-force\fR
if file already exists then overwrite.
.TP
Expand Down
160 changes: 153 additions & 7 deletions squashfs-tools/unsquashfs.c
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Original file line number Diff line number Diff line change
Expand Up @@ -105,6 +105,15 @@ unsigned int timeval;
int time_opt = FALSE;
int full_precision = FALSE;

/* should unsquashfs cross filesystem boundaries? */
int one_file_system = FALSE;
char **mp_list = NULL;
int mp_nextidx = 0, mp_count = 0;
int mp_use_fallback = FALSE;

/* initial length of the mount points list, which expands as needed */
#define MP_INITIAL_ELEMENTS 8

/* extended attribute flags */
int no_xattrs = XATTR_DEF;
regex_t *xattr_exclude_preg = NULL;
Expand Down Expand Up @@ -1208,14 +1217,18 @@ int create_inode(char *pathname, struct inode *i)
if(force)
unlink(pathname);

if(link(link_path, pathname) == -1) {
if(link(link_path, pathname) == 0) {
hardlnk_count++;
return TRUE;
}
else if(one_file_system || errno != EXDEV) {
EXIT_UNSQUASH_IGNORE("create_inode: failed to create"
" hardlink, because %s\n", strerror(errno));
return FALSE;
}

hardlnk_count++;
return TRUE;
/* trying to dereference hard link outside filesystem boundaries */
TRACE("create_inode: hard link across different mounts\n");
}

switch(i->type) {
Expand Down Expand Up @@ -2061,6 +2074,121 @@ int follow_path(char *path, char *name, unsigned int start_block,
}


void grow_mounts_list(void)
{
/* Mount points list will be expanded as needed */
int i, cnt = (mp_count ? mp_count << 1: MP_INITIAL_ELEMENTS);
size_t buflen = sizeof(mp_list[0]) * cnt;

mp_list = (char **) realloc((void *)mp_list, buflen);
if(!mp_list)
MEM_ERROR();
for(i = mp_count; i < cnt; i++)
mp_list[i] = NULL;
mp_count = cnt;
}


void free_mounts_list(void)
{
if(!mp_list)
return;
for(int i = 0; i < mp_nextidx; i++)
free((void *)mp_list[i]);
mp_count = mp_nextidx = 0;
free((void *)mp_list);
mp_list = NULL;
}


void load_mounts_list(const char *root)
{
char linebuf[1024];
char *start, *end;
size_t slen;
FILE *fp;

/* Read the second field from /proc/mounts if /proc is mounted,
* and write to mp_list[] only those mount points that start with
* <root>. With reading errors a fallback will be used. This code
* is based on mountpoint.c from the sysvinit-utils package. */
if((fp = fopen("/proc/mounts", "r")) == NULL) {
mp_use_fallback = TRUE;
return;
}
slen = strlen(root);
TRACE("load_mounts_list: locate %s\n", root);

for(;;) {
/* Read each input line into <linebuf> */
if(!fgets(linebuf, sizeof(linebuf), fp)) {
if(feof(fp))
break;
mp_use_fallback = TRUE;
free_mounts_list();
break;
}

/* Locate the second field inside <linebuf> */
start = linebuf;
while(*start != ' ')
start ++;
end = ++start;
while(*end != ' ')
end ++;
*end = '\0';

/* Save only mount points that start with <root> */
if(!strncmp(root, start, slen)) {
if(mp_nextidx >= mp_count)
grow_mounts_list();
if((mp_list[mp_nextidx++] = strdup(start)) == NULL)
MEM_ERROR();
TRACE("load_mounts_list: added %s\n", start);
}
}

fclose(fp);
}


int is_mpoint(const char* p)
{
TRACE("is_mpoint: check %s\n", p);

/* Primary way: check <p> by short list. It's very fast. */
if(mp_list) {
for(int i = 0; i < mp_nextidx; i++)
if(!strcmp(mp_list[i], p))
return TRUE;
return FALSE;
}

/* This fallback slows down unsquashfs and is only used when /proc
* is not mounted. This code is based on mountpoint.c from the
* sysvinit-utils package. Unfortunately, not all bind mounts
* can be caught this way. */
if(!mp_use_fallback)
return FALSE;
struct stat st1, st2;
char *newp;

if(lstat(p, &st1))
return FALSE;
if(!S_ISDIR(st1.st_mode))
return FALSE;
if(asprintf(&newp, "%s/..", p) == -1)
MEM_ERROR();
if(stat(newp, &st2)) {
free(newp);
return FALSE;
}
free(newp);

return (st1.st_dev != st2.st_dev) || (st1.st_ino == st2.st_ino);
}


int pre_scan(char *parent_name, unsigned int start_block, unsigned int offset,
struct pathnames *extracts, struct pathnames *excludes, int depth)
{
Expand All @@ -2081,6 +2209,12 @@ int pre_scan(char *parent_name, unsigned int start_block, unsigned int offset,
if(inumber_lookup(i->inode_number))
EXIT_UNSQUASH("File System corrupted: directory loop detected\n");

if(!lsonly && depth != 1 && one_file_system && is_mpoint(parent_name)) {
TRACE("pre_scan: skipping mount point %s\n", parent_name);
squashfs_closedir(dir);
return TRUE;
}

while(squashfs_readdir(dir, &name, &start_block, &offset, &type)) {
struct inode *i;
char *pathname;
Expand All @@ -2102,7 +2236,7 @@ int pre_scan(char *parent_name, unsigned int start_block, unsigned int offset,
MEM_ERROR();

if(type == SQUASHFS_DIR_TYPE) {
res = pre_scan(parent_name, start_block, offset, newt,
res = pre_scan(pathname, start_block, offset, newt,
newc, depth + 1);
if(res == FALSE)
scan_res = FALSE;
Expand Down Expand Up @@ -2135,6 +2269,7 @@ int dir_scan(char *parent_name, unsigned int start_block, unsigned int offset,
{
unsigned int type;
int scan_res = TRUE;
int mp = FALSE;
char *name;
struct pathnames *newt, *newc = NULL;
struct inode *i;
Expand Down Expand Up @@ -2164,8 +2299,11 @@ int dir_scan(char *parent_name, unsigned int start_block, unsigned int offset,
/*
* Skip directory if mkdir fails, unless we're
* forcing and the error is -EEXIST
* or if this directory is a mount point
*/
if((depth != 1 && !force) || errno != EEXIST) {
if(depth != 1 && errno == EEXIST)
mp = is_mpoint(parent_name);
if((depth != 1 && !force && !mp) || errno != EEXIST) {
EXIT_UNSQUASH_IGNORE("dir_scan: failed to make"
" directory %s, because %s\n",
parent_name, strerror(errno));
Expand All @@ -2189,7 +2327,10 @@ int dir_scan(char *parent_name, unsigned int start_block, unsigned int offset,
}
}

if(max_depth == -1 || depth <= max_depth) {
if(mp && one_file_system) {
TRACE("dir_scan: skipping mount point %s\n", parent_name);
}
else if(max_depth == -1 || depth <= max_depth) {
while(squashfs_readdir(dir, &name, &start_block, &offset,
&type)) {
char *pathname;
Expand Down Expand Up @@ -4224,6 +4365,8 @@ int parse_options(int argc, char *argv[])
no_wildcards = TRUE;
else if(strcmp(argv[i], "-UTC") == 0)
use_localtime = FALSE;
else if(strcmp(argv[i], "-one-file-system") == 0)
one_file_system = TRUE;
else if(strcmp(argv[i], "-strict-errors") == 0 ||
strcmp(argv[i], "-st") == 0)
strict_errors = TRUE;
Expand Down Expand Up @@ -4573,8 +4716,10 @@ int main(int argc, char *argv[])
else
data_buffer_size <<= 20 - block_log;

if(!lsonly)
if(!lsonly) {
load_mounts_list(dest);
initialise_threads(fragment_buffer_size, data_buffer_size, cat_files);
}

res = s_ops->read_filesystem_tables();
if(res == FALSE)
Expand Down Expand Up @@ -4636,6 +4781,7 @@ int main(int argc, char *argv[])
res = (long) queue_get(from_writer);
if(res == TRUE && set_exit_code)
exit_code = 2;
free_mounts_list();
}

disable_progress_bar();
Expand Down