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btrfs-progs: fix overly strict is_same_loop_file() #938

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btrfs-progs: fix overly strict is_same_loop_file() #938

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65 changes: 58 additions & 7 deletions common/path-utils.c
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Original file line number Diff line number Diff line change
Expand Up @@ -124,7 +124,9 @@ static int is_loop_device(const char *device)
* the associated file (e.g. /images/my_btrfs.img) using
* loopdev API
*/
static int resolve_loop_device_with_loopdev(const char* loop_dev, char* loop_file)
static int resolve_loop_device_with_loopdev(const char* loop_dev, char* loop_file,
unsigned long long *offset,
unsigned long long *sizelimit)
{
int fd;
int ret;
Expand All @@ -142,6 +144,9 @@ static int resolve_loop_device_with_loopdev(const char* loop_dev, char* loop_fil
memcpy(loop_file, lo64.lo_file_name, sizeof(lo64.lo_file_name));
loop_file[sizeof(lo64.lo_file_name)] = 0;

*offset = lo64.lo_offset;
*sizelimit = lo64.lo_sizelimit;

out:
close(fd);

Expand All @@ -153,24 +158,30 @@ static int resolve_loop_device_with_loopdev(const char* loop_dev, char* loop_fil
* the associated file (e.g. /images/my_btrfs.img)
*/
static int resolve_loop_device(const char* loop_dev, char* loop_file,
int max_len)
int max_len, unsigned long long *offset,
unsigned long long *sizelimit)
{
int ret;
FILE *f;
char fmt[20];
char p[PATH_MAX];
char real_loop_dev[PATH_MAX];
char *name;

if (!realpath(loop_dev, real_loop_dev))
return -errno;
snprintf(p, PATH_MAX, "/sys/block/%s/loop/backing_file", strrchr(real_loop_dev, '/'));

name = strrchr(real_loop_dev, '/');

snprintf(p, PATH_MAX, "/sys/block/%s/loop/backing_file", name);
if (!(f = fopen(p, "r"))) {
if (errno == ENOENT)
/*
* It's possibly a partitioned loop device, which is
* resolvable with loopdev API.
*/
return resolve_loop_device_with_loopdev(loop_dev, loop_file);
return resolve_loop_device_with_loopdev(loop_dev, loop_file,
offset, sizelimit);
return -errno;
}

Expand All @@ -180,6 +191,24 @@ static int resolve_loop_device(const char* loop_dev, char* loop_file,
if (ret == EOF)
return -errno;

snprintf(p, PATH_MAX, "/sys/block/%s/loop/offset", name);
if (!(f = fopen(p, "r")))
return -errno;

ret = fscanf(f, "%llu", offset);
fclose(f);
if (ret == EOF)
return -errno;

snprintf(p, PATH_MAX, "/sys/block/%s/loop/sizelimit", name);
if (!(f = fopen(p, "r")))
return -errno;

ret = fscanf(f, "%llu", sizelimit);
fclose(f);
if (ret == EOF)
return -errno;

return 0;
}

Expand Down Expand Up @@ -235,14 +264,17 @@ int is_same_loop_file(const char *a, const char *b)
const char* final_a = NULL;
const char* final_b = NULL;
int ret;
unsigned long long a_offset, a_sizelimit, b_offset, b_sizelimit;
unsigned long long low_offset, low_sizelimit, high_offset;

/* Resolve a if it is a loop device */
if ((ret = is_loop_device(a)) < 0) {
if (ret == -ENOENT)
return 0;
return ret;
} else if (ret) {
ret = resolve_loop_device(a, res_a, sizeof(res_a));
ret = resolve_loop_device(a, res_a, sizeof(res_a),
&a_offset, &a_sizelimit);
if (ret < 0) {
if (errno != EPERM)
return ret;
Expand All @@ -259,7 +291,8 @@ int is_same_loop_file(const char *a, const char *b)
return 0;
return ret;
} else if (ret) {
ret = resolve_loop_device(b, res_b, sizeof(res_b));
ret = resolve_loop_device(b, res_b, sizeof(res_b),
&b_offset, &b_sizelimit);
if (ret < 0) {
if (errno != EPERM)
return ret;
Expand All @@ -270,7 +303,25 @@ int is_same_loop_file(const char *a, const char *b)
final_b = b;
}

return is_same_blk_file(final_a, final_b);
if (!is_same_blk_file(final_a, final_b))
return 0;

/* If no size limit, this is the base block device. */
if (a_sizelimit == 0 || b_sizelimit == 0)
return 1;

/* If the loop devices don't overlap, there's no problem. */
if (a_offset < b_offset) {
low_offset = a_offset;
low_sizelimit = a_sizelimit;
high_offset = b_offset;
} else {
low_offset = b_offset;
low_sizelimit = b_sizelimit;
high_offset = a_offset;
}

return low_offset + low_sizelimit > high_offset ? 1 : 0;
}

/* Checks if a file exists and is a block or regular file*/
Expand Down