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Fix race while allocating free loop device.

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Fixes Issue #314.

Thanks to Martin Jeřábek for the report.
This commit is contained in:
Milan Broz
2017-01-20 15:27:40 +01:00
parent 945249fd02
commit 3b02c1e690
4 changed files with 48 additions and 59 deletions
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36
lib/utils_loop.c
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@@ -19,6 +19,7 @@
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <unistd.h>
@@ -73,7 +74,7 @@ static char *crypt_loop_get_device_old(void)
return NULL;
}
char *crypt_loop_get_device(void)
static char *crypt_loop_get_device(void)
{
char dev[64];
int i, loop_fd;
@@ -99,13 +100,15 @@ char *crypt_loop_get_device(void)
return strdup(dev);
}
int crypt_loop_attach(const char *loop, const char *file, int offset,
int crypt_loop_attach(char **loop, const char *file, int offset,
int autoclear, int *readonly)
{
struct loop_info64 lo64 = {0};
char *lo_file_name;
int loop_fd = -1, file_fd = -1, r = 1;
*loop = NULL;
file_fd = open(file, (*readonly ? O_RDONLY : O_RDWR) | O_EXCL);
if (file_fd < 0 && (errno == EROFS || errno == EACCES) && !*readonly) {
*readonly = 1;
@@ -114,9 +117,25 @@ int crypt_loop_attach(const char *loop, const char *file, int offset,
if (file_fd < 0)
goto out;
loop_fd = open(loop, *readonly ? O_RDONLY : O_RDWR);
if (loop_fd < 0)
goto out;
while (loop_fd < 0) {
*loop = crypt_loop_get_device();
if (!*loop)
goto out;
loop_fd = open(*loop, *readonly ? O_RDONLY : O_RDWR);
if (loop_fd < 0)
goto out;
if (ioctl(loop_fd, LOOP_SET_FD, file_fd) < 0) {
if (errno != EBUSY)
goto out;
free(*loop);
*loop = NULL;
close(loop_fd);
loop_fd = -1;
}
}
lo_file_name = (char*)lo64.lo_file_name;
lo_file_name[LO_NAME_SIZE-1] = '\0';
@@ -125,9 +144,6 @@ int crypt_loop_attach(const char *loop, const char *file, int offset,
if (autoclear)
lo64.lo_flags |= LO_FLAGS_AUTOCLEAR;
if (ioctl(loop_fd, LOOP_SET_FD, file_fd) < 0)
goto out;
if (ioctl(loop_fd, LOOP_SET_STATUS64, &lo64) < 0) {
(void)ioctl(loop_fd, LOOP_CLR_FD, 0);
goto out;
@@ -149,6 +165,10 @@ out:
close(loop_fd);
if (file_fd >= 0)
close(file_fd);
if (r && *loop) {
free(*loop);
*loop = NULL;
}
return r ? -1 : loop_fd;
}