| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Date: Wed, 26 Apr 2023 20:05:03 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: Al Viro <viro@...iv.linux.org.uk>,
Jiri Slaby <jirislaby@...nel.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Dmitry Vyukov <dvyukov@...gle.com>,
syzbot <syzbot+b7c3ba8cdc2f6cf83c21@...kaller.appspotmail.com>,
linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: [PATCH] tty: tty_io: remove hung_up_tty_fops
syzbot is reporting data race between __tty_hangup() and __fput(), for
filp->f_op readers are not holding tty->files_lock.
Dmitry Vyukov mentioned that this race has possibility of NULL pointer
dereference, for tty_fops implements e.g. splice_read callback whereas
hung_up_tty_fops does not.
CPU0 CPU1
---- ----
do_splice_to() {
__tty_hangup() {
// f_op->splice_read was generic_file_splice_read
if (unlikely(!in->f_op->splice_read))
return warn_unsupported(in, "read");
filp->f_op = &hung_up_tty_fops;
// f_op->splice_read is now NULL
return in->f_op->splice_read(in, ppos, pipe, len, flags);
}
}
If we care about only NULL pointer dereference, implementing missing
callbacks to hung_up_tty_fops is fine. But if we also care about KCSAN
reports, we will need to wrap all filp->f_op usages which are reachable
via tty_fops callbacks using data_race().
Such wrapping is overkill as a fix for tty_io code. Therefore, instead of
implementing missing callbacks, stop updating filp->f_op and remove
hung_up_tty_fops. Then, changes will be limited to within tty_io code.
tty_open() is doing "filp->f_op = &tty_fops;".
__tty_hangup() is doing "filp->f_op = &hung_up_tty_fops;".
tty_hung_up_p() is doing "filp->f_op == &hung_up_tty_fops", and
most functions are checking tty_hung_up_p().
Since tty_open() allocates "struct tty_file_private" for each
"struct file", we can remember whether __tty_hangup() was called
by adding a flag to "struct tty_file_private".
Below is detail of where/what to change.
Regarding __tty_hangup(), replace "filp->f_op = &hung_up_tty_fops;" with
setting the above-mentioned flag.
Regarding tty_hungup_p(), replace "filp->f_op == &hung_up_tty_fops" with
"filp->f_op == &tty_fops" and check the above-mentioned flag.
Regarding tty_open(), just remove "filp->f_op = &tty_fops;" because
"struct tty_file_private" was already released by tty_del_file() from
tty_release() when control reaches this line.
Regarding tty_{read,write,poll,ioctl,compat_ioctl}(), respectively embed
hung_up_tty_{read,write,poll,ioctl,compat_ioctl}() right before
tty_paranoia_check().
Regarding tty_fasync(), embed hung_up_tty_fasync() right before tty_lock()
in tty_fasync() rather than tty_paranoia_check() in __tty_fasync(), for
tty_hung_up_p() is checked right after tty_lock() returned.
Since tty_read() is called via file->f_op->read_iter() from
call_read_iter() from generic_file_splice_read(), no change is needed for
tty_fops->splice_read.
Since tty_write() is called via file->f_op->write_iter() from
call_write_iter() from do_iter_readv_writev() from do_iter_write() from
vfs_iter_write() from iter_file_splice_write(), no change is needed for
tty_fops->splice_write.
Since both tty_fops and hung_up_tty_fops point to the same callback for
llseek/release, no change is needed for tty_fops->{llseek,release}.
Finally, remove hung_up_tty_fops.
Reported-by: syzbot <syzbot+b7c3ba8cdc2f6cf83c21@...kaller.appspotmail.com>
Link: https://syzkaller.appspot.com/bug?extid=b7c3ba8cdc2f6cf83c21
Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc: Dmitry Vyukov <dvyukov@...gle.com>
---
drivers/tty/tty_io.c | 37 ++++++++++++++++++-------------------
include/linux/tty.h | 1 +
2 files changed, 19 insertions(+), 19 deletions(-)
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 36fb945fdad4..c1748e4da233 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -182,7 +182,7 @@ int tty_alloc_file(struct file *file)
{
struct tty_file_private *priv;
- priv = kmalloc(sizeof(*priv), GFP_KERNEL);
+ priv = kzalloc(sizeof(*priv), GFP_KERNEL);
if (!priv)
return -ENOMEM;
@@ -491,17 +491,6 @@ static const struct file_operations console_fops = {
.fasync = tty_fasync,
};
-static const struct file_operations hung_up_tty_fops = {
- .llseek = no_llseek,
- .read_iter = hung_up_tty_read,
- .write_iter = hung_up_tty_write,
- .poll = hung_up_tty_poll,
- .unlocked_ioctl = hung_up_tty_ioctl,
- .compat_ioctl = hung_up_tty_compat_ioctl,
- .release = tty_release,
- .fasync = hung_up_tty_fasync,
-};
-
static DEFINE_SPINLOCK(redirect_lock);
static struct file *redirect;
@@ -619,7 +608,8 @@ static void __tty_hangup(struct tty_struct *tty, int exit_session)
continue;
closecount++;
__tty_fasync(-1, filp, 0); /* can't block */
- filp->f_op = &hung_up_tty_fops;
+ /* Accept race with tty_hung_up_p() test. */
+ data_race(priv->hung = true);
}
spin_unlock(&tty->files_lock);
@@ -743,7 +733,9 @@ void tty_vhangup_session(struct tty_struct *tty)
*/
int tty_hung_up_p(struct file *filp)
{
- return (filp && filp->f_op == &hung_up_tty_fops);
+ return filp && filp->f_op == &tty_fops &&
+ /* Accept race with __tty_hangup(). */
+ data_race(((struct tty_file_private *) filp->private_data)->hung);
}
EXPORT_SYMBOL(tty_hung_up_p);
@@ -911,6 +903,8 @@ static ssize_t tty_read(struct kiocb *iocb, struct iov_iter *to)
struct tty_struct *tty = file_tty(file);
struct tty_ldisc *ld;
+ if (tty_hung_up_p(file))
+ return hung_up_tty_read(iocb, to);
if (tty_paranoia_check(tty, inode, "tty_read"))
return -EIO;
if (!tty || tty_io_error(tty))
@@ -1073,6 +1067,8 @@ static ssize_t file_tty_write(struct file *file, struct kiocb *iocb, struct iov_
struct tty_ldisc *ld;
ssize_t ret;
+ if (tty_hung_up_p(file))
+ return hung_up_tty_write(iocb, from);
if (tty_paranoia_check(tty, file_inode(file), "tty_write"))
return -EIO;
if (!tty || !tty->ops->write || tty_io_error(tty))
@@ -2159,11 +2155,6 @@ static int tty_open(struct inode *inode, struct file *filp)
return retval;
schedule();
- /*
- * Need to reset f_op in case a hangup happened.
- */
- if (tty_hung_up_p(filp))
- filp->f_op = &tty_fops;
goto retry_open;
}
clear_bit(TTY_HUPPED, &tty->flags);
@@ -2197,6 +2188,8 @@ static __poll_t tty_poll(struct file *filp, poll_table *wait)
struct tty_ldisc *ld;
__poll_t ret = 0;
+ if (tty_hung_up_p(filp))
+ return hung_up_tty_poll(filp, wait);
if (tty_paranoia_check(tty, file_inode(filp), "tty_poll"))
return 0;
@@ -2249,6 +2242,8 @@ static int tty_fasync(int fd, struct file *filp, int on)
struct tty_struct *tty = file_tty(filp);
int retval = -ENOTTY;
+ if (tty_hung_up_p(filp))
+ return hung_up_tty_fasync(fd, filp, on);
tty_lock(tty);
if (!tty_hung_up_p(filp))
retval = __tty_fasync(fd, filp, on);
@@ -2658,6 +2653,8 @@ long tty_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
int retval;
struct tty_ldisc *ld;
+ if (tty_hung_up_p(file))
+ return hung_up_tty_ioctl(file, cmd, arg);
if (tty_paranoia_check(tty, file_inode(file), "tty_ioctl"))
return -EINVAL;
@@ -2943,6 +2940,8 @@ static long tty_compat_ioctl(struct file *file, unsigned int cmd,
return tty_ioctl(file, cmd, arg);
}
+ if (tty_hung_up_p(file))
+ return hung_up_tty_compat_ioctl(file, cmd, arg);
if (tty_paranoia_check(tty, file_inode(file), "tty_ioctl"))
return -EINVAL;
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 093935e97f42..d7fa18f8c526 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -255,6 +255,7 @@ struct tty_file_private {
struct tty_struct *tty;
struct file *file;
struct list_head list;
+ bool hung;
};
/**
--
2.34.1
Powered by blists - more mailing lists