From b790f210fe8423eff881b2a8a93ba5dbc45534d0 Mon Sep 17 00:00:00 2001 From: Michael Welling Date: Fri, 25 Apr 2014 19:27:48 -0500 Subject: tty: serial: 8250_core.c Bug fix for Exar chips. MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The sleep function was updated to put the serial port to sleep only when necessary. This appears to resolve the errant behavior of the driver as described in Kernel Bug 61961 – "My Exar Corp. XR17C/D152 Dual PCI UART modem does not work with 3.8.0". Signed-off-by: Michael Welling Cc: stable Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/8250/8250_core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'drivers') diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c index 0e1bf8858431..2d4bd3929e50 100644 --- a/drivers/tty/serial/8250/8250_core.c +++ b/drivers/tty/serial/8250/8250_core.c @@ -555,7 +555,7 @@ static void serial8250_set_sleep(struct uart_8250_port *p, int sleep) */ if ((p->port.type == PORT_XR17V35X) || (p->port.type == PORT_XR17D15X)) { - serial_out(p, UART_EXAR_SLEEP, 0xff); + serial_out(p, UART_EXAR_SLEEP, sleep ? 0xff : 0); return; } -- cgit v1.2.3 From 4291086b1f081b869c6d79e5b7441633dc3ace00 Mon Sep 17 00:00:00 2001 From: Peter Hurley Date: Sat, 3 May 2014 14:04:59 +0200 Subject: n_tty: Fix n_tty_write crash when echoing in raw mode The tty atomic_write_lock does not provide an exclusion guarantee for the tty driver if the termios settings are LECHO & !OPOST. And since it is unexpected and not allowed to call TTY buffer helpers like tty_insert_flip_string concurrently, this may lead to crashes when concurrect writers call pty_write. In that case the following two writers: * the ECHOing from a workqueue and * pty_write from the process race and can overflow the corresponding TTY buffer like follows. If we look into tty_insert_flip_string_fixed_flag, there is: int space = __tty_buffer_request_room(port, goal, flags); struct tty_buffer *tb = port->buf.tail; ... memcpy(char_buf_ptr(tb, tb->used), chars, space); ... tb->used += space; so the race of the two can result in something like this: A B __tty_buffer_request_room __tty_buffer_request_room memcpy(buf(tb->used), ...) tb->used += space; memcpy(buf(tb->used), ...) ->BOOM B's memcpy is past the tty_buffer due to the previous A's tb->used increment. Since the N_TTY line discipline input processing can output concurrently with a tty write, obtain the N_TTY ldisc output_lock to serialize echo output with normal tty writes. This ensures the tty buffer helper tty_insert_flip_string is not called concurrently and everything is fine. Note that this is nicely reproducible by an ordinary user using forkpty and some setup around that (raw termios + ECHO). And it is present in kernels at least after commit d945cb9cce20ac7143c2de8d88b187f62db99bdc (pty: Rework the pty layer to use the normal buffering logic) in 2.6.31-rc3. js: add more info to the commit log js: switch to bool js: lock unconditionally js: lock only the tty->ops->write call References: CVE-2014-0196 Reported-and-tested-by: Jiri Slaby Signed-off-by: Peter Hurley Signed-off-by: Jiri Slaby Cc: Linus Torvalds Cc: Alan Cox Cc: Signed-off-by: Greg Kroah-Hartman --- drivers/tty/n_tty.c | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'drivers') diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c index 41fe8a047d37..fe9d129c8735 100644 --- a/drivers/tty/n_tty.c +++ b/drivers/tty/n_tty.c @@ -2353,8 +2353,12 @@ static ssize_t n_tty_write(struct tty_struct *tty, struct file *file, if (tty->ops->flush_chars) tty->ops->flush_chars(tty); } else { + struct n_tty_data *ldata = tty->disc_data; + while (nr > 0) { + mutex_lock(&ldata->output_lock); c = tty->ops->write(tty, b, nr); + mutex_unlock(&ldata->output_lock); if (c < 0) { retval = c; goto break_out; -- cgit v1.2.3 From 501fed45b7e8836ee9373f4d31e2d85e3db6103a Mon Sep 17 00:00:00 2001 From: Tomoki Sekiyama Date: Fri, 2 May 2014 18:58:24 -0400 Subject: drivers/tty/hvc: don't free hvc_console_setup after init When 'console=hvc0' is specified to the kernel parameter in x86 KVM guest, hvc console is setup within a kthread. However, that will cause SEGV and the boot will fail when the driver is builtin to the kernel, because currently hvc_console_setup() is annotated with '__init'. This patch removes '__init' to boot the guest successfully with 'console=hvc0'. Signed-off-by: Tomoki Sekiyama Cc: stable Signed-off-by: Greg Kroah-Hartman --- drivers/tty/hvc/hvc_console.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'drivers') diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c index 94f9e3a38412..0ff7fda0742f 100644 --- a/drivers/tty/hvc/hvc_console.c +++ b/drivers/tty/hvc/hvc_console.c @@ -190,7 +190,7 @@ static struct tty_driver *hvc_console_device(struct console *c, int *index) return hvc_driver; } -static int __init hvc_console_setup(struct console *co, char *options) +static int hvc_console_setup(struct console *co, char *options) { if (co->index < 0 || co->index >= MAX_NR_HVC_CONSOLES) return -ENODEV; -- cgit v1.2.3 From 5fbf1a65dd53ef313783c34a0e93a6e29def6136 Mon Sep 17 00:00:00 2001 From: Peter Hurley Date: Fri, 2 May 2014 10:56:11 -0400 Subject: Revert "tty: Fix race condition between __tty_buffer_request_room and flush_to_ldisc" This reverts commit 6a20dbd6caa2358716136144bf524331d70b1e03. Although the commit correctly identifies an unsafe race condition between __tty_buffer_request_room() and flush_to_ldisc(), the commit fixes the race with an unnecessary spinlock in a lockless algorithm. The follow-on commit, "tty: Fix lockless tty buffer race" fixes the race locklessly. Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman --- drivers/tty/tty_buffer.c | 16 ++-------------- include/linux/tty.h | 1 - 2 files changed, 2 insertions(+), 15 deletions(-) (limited to 'drivers') diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c index f1d30f6945af..8ebd9f88a6f6 100644 --- a/drivers/tty/tty_buffer.c +++ b/drivers/tty/tty_buffer.c @@ -255,16 +255,11 @@ static int __tty_buffer_request_room(struct tty_port *port, size_t size, if (change || left < size) { /* This is the slow path - looking for new buffers to use */ if ((n = tty_buffer_alloc(port, size)) != NULL) { - unsigned long iflags; - n->flags = flags; buf->tail = n; - - spin_lock_irqsave(&buf->flush_lock, iflags); b->commit = b->used; + smp_mb(); b->next = n; - spin_unlock_irqrestore(&buf->flush_lock, iflags); - } else if (change) size = 0; else @@ -448,7 +443,6 @@ static void flush_to_ldisc(struct work_struct *work) mutex_lock(&buf->lock); while (1) { - unsigned long flags; struct tty_buffer *head = buf->head; int count; @@ -456,19 +450,14 @@ static void flush_to_ldisc(struct work_struct *work) if (atomic_read(&buf->priority)) break; - spin_lock_irqsave(&buf->flush_lock, flags); count = head->commit - head->read; if (!count) { - if (head->next == NULL) { - spin_unlock_irqrestore(&buf->flush_lock, flags); + if (head->next == NULL) break; - } buf->head = head->next; - spin_unlock_irqrestore(&buf->flush_lock, flags); tty_buffer_free(port, head); continue; } - spin_unlock_irqrestore(&buf->flush_lock, flags); count = receive_buf(tty, head, count); if (!count) @@ -523,7 +512,6 @@ void tty_buffer_init(struct tty_port *port) struct tty_bufhead *buf = &port->buf; mutex_init(&buf->lock); - spin_lock_init(&buf->flush_lock); tty_buffer_reset(&buf->sentinel, 0); buf->head = &buf->sentinel; buf->tail = &buf->sentinel; diff --git a/include/linux/tty.h b/include/linux/tty.h index 036cccd80d9f..1c3316a47d7e 100644 --- a/include/linux/tty.h +++ b/include/linux/tty.h @@ -61,7 +61,6 @@ struct tty_bufhead { struct tty_buffer *head; /* Queue head */ struct work_struct work; struct mutex lock; - spinlock_t flush_lock; atomic_t priority; struct tty_buffer sentinel; struct llist_head free; /* Free queue head */ -- cgit v1.2.3 From 62a0d8d7c2b29f92850e4ee3c38e5dfd936e92b2 Mon Sep 17 00:00:00 2001 From: Peter Hurley Date: Fri, 2 May 2014 10:56:12 -0400 Subject: tty: Fix lockless tty buffer race Commit 6a20dbd6caa2358716136144bf524331d70b1e03, "tty: Fix race condition between __tty_buffer_request_room and flush_to_ldisc" correctly identifies an unsafe race condition between __tty_buffer_request_room() and flush_to_ldisc(), where the consumer flush_to_ldisc() prematurely advances the head before consuming the last of the data committed. For example: CPU 0 | CPU 1 __tty_buffer_request_room | flush_to_ldisc ... | ... | count = head->commit - head->read n = tty_buffer_alloc() | b->commit = b->used | b->next = n | | if (!count) /* T */ | if (head->next == NULL) /* F */ | buf->head = head->next In this case, buf->head has been advanced but head->commit may have been updated with a new value. Instead of reintroducing an unnecessary lock, fix the race locklessly. Read the commit-next pair in the reverse order of writing, which guarantees the commit value read is the latest value written if the head is advancing. Reported-by: Manfred Schlaegl Cc: # 3.12.x+ Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman --- drivers/tty/tty_buffer.c | 17 ++++++++++++++--- 1 file changed, 14 insertions(+), 3 deletions(-) (limited to 'drivers') diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c index 8ebd9f88a6f6..cf78d1985cd8 100644 --- a/drivers/tty/tty_buffer.c +++ b/drivers/tty/tty_buffer.c @@ -258,7 +258,11 @@ static int __tty_buffer_request_room(struct tty_port *port, size_t size, n->flags = flags; buf->tail = n; b->commit = b->used; - smp_mb(); + /* paired w/ barrier in flush_to_ldisc(); ensures the + * latest commit value can be read before the head is + * advanced to the next buffer + */ + smp_wmb(); b->next = n; } else if (change) size = 0; @@ -444,17 +448,24 @@ static void flush_to_ldisc(struct work_struct *work) while (1) { struct tty_buffer *head = buf->head; + struct tty_buffer *next; int count; /* Ldisc or user is trying to gain exclusive access */ if (atomic_read(&buf->priority)) break; + next = head->next; + /* paired w/ barrier in __tty_buffer_request_room(); + * ensures commit value read is not stale if the head + * is advancing to the next buffer + */ + smp_rmb(); count = head->commit - head->read; if (!count) { - if (head->next == NULL) + if (next == NULL) break; - buf->head = head->next; + buf->head = next; tty_buffer_free(port, head); continue; } -- cgit v1.2.3