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authorJiri Olsa <jolsa@redhat.com>2011-02-07 19:31:24 +0100
committerGreg Kroah-Hartman <gregkh@suse.de>2011-02-17 11:13:19 -0800
commitdc1892c4bc6960121ca4c8023a07c815cfd689be (patch)
tree8dde17673ca49a3605c45dead92217926d839c3a /drivers/tty/vt
parent1ffdda950394b6da54d68e9643bc691ebad7a6cc (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>
Diffstat (limited to 'drivers/tty/vt')
-rw-r--r--drivers/tty/vt/vc_screen.c18
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)
int size;
mutex_lock(&con_buf_mtx);
+ console_lock();
size = vcs_size(file->f_path.dentry->d_inode);
+ console_unlock();
+ if (size < 0) {
+ mutex_unlock(&con_buf_mtx);
+ return size;
+ }
switch (orig) {
default:
mutex_unlock(&con_buf_mtx);
@@ -237,6 +243,12 @@ vcs_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
* could sleep.
*/
size = vcs_size(inode);
+ if (size < 0) {
+ if (read)
+ break;
+ ret = size;
+ goto unlock_out;
+ }
if (pos >= size)
break;
if (count > size - pos)
@@ -436,6 +448,12 @@ vcs_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
* Return data written up to now on failure.
*/
size = vcs_size(inode);
+ if (size < 0) {
+ if (written)
+ break;
+ ret = size;
+ goto unlock_out;
+ }
if (pos >= size)
break;
if (this_round > size - pos)