diff options
author | Jiri Olsa <jolsa@redhat.com> | 2011-02-07 13:31:24 -0500 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@suse.de> | 2011-02-17 14:13:19 -0500 |
commit | dc1892c4bc6960121ca4c8023a07c815cfd689be (patch) | |
tree | 8dde17673ca49a3605c45dead92217926d839c3a | |
parent | 1ffdda950394b6da54d68e9643bc691ebad7a6cc (diff) |
tty,vcs: lseek/VC-release race fix
there's a race between vcs's lseek handler and VC release.
The lseek handler does not hold console_lock and touches
VC's size info. If during this the VC got released, there's
an access violation.
Following program triggers the issue for me:
[SNIP]
#define _BSD_SOURCE
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <linux/vt.h>
#include <unistd.h>
#include <errno.h>
static int run_seek(void)
{
while(1) {
int fd;
fd = open("./vcs30", O_RDWR);
while(lseek(fd, 0, 0) != -1);
close(fd);
}
}
static int open_ioctl_tty(void)
{
return open("/dev/tty1", O_RDWR);
}
static int do_ioctl(int fd, int req, int i)
{
return ioctl(fd, req, i);
}
#define INIT(i) do_ioctl(ioctl_fd, VT_ACTIVATE, i)
#define SHUT(i) do_ioctl(ioctl_fd, VT_DISALLOCATE, i)
int main(int argc, char **argv)
{
int ioctl_fd = open_ioctl_tty();
if (ioctl < 0) {
perror("open tty1 failed\n");
return -1;
}
if ((-1 == mknod("vcs30", S_IFCHR|0666, makedev(7, 30))) &&
(errno != EEXIST)) {
printf("errno %d\n", errno);
perror("failed to create vcs30");
return -1;
}
do_ioctl(ioctl_fd, VT_LOCKSWITCH, 0);
if (!fork())
run_seek();
while(1) {
INIT(30);
SHUT(30);
}
return 0;
}
[SNIP]
Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
-rw-r--r-- | drivers/tty/vt/vc_screen.c | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/drivers/tty/vt/vc_screen.c b/drivers/tty/vt/vc_screen.c index a672ed192d33..3c27c4bc6040 100644 --- a/drivers/tty/vt/vc_screen.c +++ b/drivers/tty/vt/vc_screen.c | |||
@@ -159,7 +159,13 @@ static loff_t vcs_lseek(struct file *file, loff_t offset, int orig) | |||
159 | int size; | 159 | int size; |
160 | 160 | ||
161 | mutex_lock(&con_buf_mtx); | 161 | mutex_lock(&con_buf_mtx); |
162 | console_lock(); | ||
162 | size = vcs_size(file->f_path.dentry->d_inode); | 163 | size = vcs_size(file->f_path.dentry->d_inode); |
164 | console_unlock(); | ||
165 | if (size < 0) { | ||
166 | mutex_unlock(&con_buf_mtx); | ||
167 | return size; | ||
168 | } | ||
163 | switch (orig) { | 169 | switch (orig) { |
164 | default: | 170 | default: |
165 | mutex_unlock(&con_buf_mtx); | 171 | mutex_unlock(&con_buf_mtx); |
@@ -237,6 +243,12 @@ vcs_read(struct file *file, char __user *buf, size_t count, loff_t *ppos) | |||
237 | * could sleep. | 243 | * could sleep. |
238 | */ | 244 | */ |
239 | size = vcs_size(inode); | 245 | size = vcs_size(inode); |
246 | if (size < 0) { | ||
247 | if (read) | ||
248 | break; | ||
249 | ret = size; | ||
250 | goto unlock_out; | ||
251 | } | ||
240 | if (pos >= size) | 252 | if (pos >= size) |
241 | break; | 253 | break; |
242 | if (count > size - pos) | 254 | if (count > size - pos) |
@@ -436,6 +448,12 @@ vcs_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos) | |||
436 | * Return data written up to now on failure. | 448 | * Return data written up to now on failure. |
437 | */ | 449 | */ |
438 | size = vcs_size(inode); | 450 | size = vcs_size(inode); |
451 | if (size < 0) { | ||
452 | if (written) | ||
453 | break; | ||
454 | ret = size; | ||
455 | goto unlock_out; | ||
456 | } | ||
439 | if (pos >= size) | 457 | if (pos >= size) |
440 | break; | 458 | break; |
441 | if (this_round > size - pos) | 459 | if (this_round > size - pos) |