Messages in this thread Patch in this message | | | From | Jiri Olsa <> | Subject | [PATCH 1/2] tty,vcs: lseek/VC-release race fix | Date | Mon, 7 Feb 2011 19:31:24 +0100 |
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hi,
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]
wbr, jirka
Signed-off-by: Jiri Olsa <jolsa@redhat.com> --- 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 a672ed1..3c27c4b 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) -- 1.7.1
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