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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>
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1 changed files with 18 additions and 0 deletions
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@ -159,7 +159,13 @@ static loff_t vcs_lseek(struct file *file, loff_t offset, int orig)
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int size;
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mutex_lock(&con_buf_mtx);
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console_lock();
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size = vcs_size(file->f_path.dentry->d_inode);
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console_unlock();
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if (size < 0) {
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mutex_unlock(&con_buf_mtx);
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return size;
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}
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switch (orig) {
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default:
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mutex_unlock(&con_buf_mtx);
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@ -237,6 +243,12 @@ vcs_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
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* could sleep.
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*/
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size = vcs_size(inode);
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if (size < 0) {
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if (read)
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break;
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ret = size;
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goto unlock_out;
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}
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if (pos >= size)
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break;
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if (count > size - pos)
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@ -436,6 +448,12 @@ vcs_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
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* Return data written up to now on failure.
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*/
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size = vcs_size(inode);
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if (size < 0) {
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if (written)
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break;
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ret = size;
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goto unlock_out;
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}
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if (pos >= size)
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break;
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if (this_round > size - pos)
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