diff options
authorStefan Richter <stefanr@s5r6.in-berlin.de>2014-11-11 17:16:44 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-11-21 09:22:53 -0800
commit562e494829ef4d54cf9c6c0676038dac3e2917af (patch)
parent16640ca660f4980fb5c1f4e4febce19875f4c1b8 (diff)
firewire: cdev: prevent kernel stack leaking into ioctl arguments
commit eaca2d8e75e90a70a63a6695c9f61932609db212 upstream. Found by the UC-KLEE tool: A user could supply less input to firewire-cdev ioctls than write- or write/read-type ioctl handlers expect. The handlers used data from uninitialized kernel stack then. This could partially leak back to the user if the kernel subsequently generated fw_cdev_event_'s (to be read from the firewire-cdev fd) which notably would contain the _u64 closure field which many of the ioctl argument structures contain. The fact that the handlers would act on random garbage input is a lesser issue since all handlers must check their input anyway. The fix simply always null-initializes the entire ioctl argument buffer regardless of the actual length of expected user input. That is, a runtime overhead of memset(..., 40) is added to each firewirew-cdev ioctl() call. [Comment from Clemens Ladisch: This part of the stack is most likely to be already in the cache.] Remarks: - There was never any leak from kernel stack to the ioctl output buffer itself. IOW, it was not possible to read kernel stack by a read-type or write/read-type ioctl alone; the leak could at most happen in combination with read()ing subsequent event data. - The actual expected minimum user input of each ioctl from include/uapi/linux/firewire-cdev.h is, in bytes: [0x00] = 32, [0x05] = 4, [0x0a] = 16, [0x0f] = 20, [0x14] = 16, [0x01] = 36, [0x06] = 20, [0x0b] = 4, [0x10] = 20, [0x15] = 20, [0x02] = 20, [0x07] = 4, [0x0c] = 0, [0x11] = 0, [0x16] = 8, [0x03] = 4, [0x08] = 24, [0x0d] = 20, [0x12] = 36, [0x17] = 12, [0x04] = 20, [0x09] = 24, [0x0e] = 4, [0x13] = 40, [0x18] = 4. Reported-by: David Ramos <daramos@stanford.edu> Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
1 files changed, 1 insertions, 2 deletions
diff --git a/drivers/firewire/core-cdev.c b/drivers/firewire/core-cdev.c
index ac1b43a04285..4f73c727a97a 100644
--- a/drivers/firewire/core-cdev.c
+++ b/drivers/firewire/core-cdev.c
@@ -1637,8 +1637,7 @@ static int dispatch_ioctl(struct client *client,
_IOC_SIZE(cmd) > sizeof(buffer))
return -ENOTTY;
- if (_IOC_DIR(cmd) == _IOC_READ)
- memset(&buffer, 0, _IOC_SIZE(cmd));
+ memset(&buffer, 0, sizeof(buffer));
if (_IOC_DIR(cmd) & _IOC_WRITE)
if (copy_from_user(&buffer, arg, _IOC_SIZE(cmd)))