[PATCH] btrfs-progs: fix invalid memory write in get_fs_info()

* [PATCH] btrfs-progs: fix invalid memory write in get_fs_info()
@ 2019-06-03  1:27 damenly.su
  2019-06-05 15:56 ` David Sterba
  0 siblings, 1 reply; 2+ messages in thread
From: damenly.su @ 2019-06-03  1:27 UTC (permalink / raw)
  To: linux-btrfs; +Cc: Su Yue, Peter Hjalmarsson

From: Su Yue <Damenly_Su@gmx.com>

As the link reported, btrfs fi sh may crash while a device is removing.

valgrind reported:
======================================================================
...
==883== Invalid write of size 8
==883==    at 0x13C99A: get_device_info (in /usr/bin/btrfs)
==883==    by 0x13D715: get_fs_info (in /usr/bin/btrfs)
==883==    by 0x153B5F: ??? (in /usr/bin/btrfs)
==883==    by 0x11B0C1: main (in /usr/bin/btrfs)
==883==  Address 0x4d8c7a0 is 0 bytes after a block of size 12,288 alloc'd
==883==    at 0x483877F: malloc (vg_replace_malloc.c:299)
==883==    by 0x13D861: get_fs_info (in /usr/bin/btrfs)
==883==    by 0x153B5F: ??? (in /usr/bin/btrfs)
==883==    by 0x11B0C1: main (in /usr/bin/btrfs)
==883==
==883== Invalid write of size 8
==883==    at 0x13C99D: get_device_info (in /usr/bin/btrfs)
==883==    by 0x13D715: get_fs_info (in /usr/bin/btrfs)
==883==    by 0x153B5F: ??? (in /usr/bin/btrfs)
==883==    by 0x11B0C1: main (in /usr/bin/btrfs)
==883==  Address 0x4d8c7a8 is 8 bytes after a block of size 12,288 alloc'd
==883==    at 0x483877F: malloc (vg_replace_malloc.c:299)
==883==    by 0x13D861: get_fs_info (in /usr/bin/btrfs)
==883==    by 0x153B5F: ??? (in /usr/bin/btrfs)
==883==    by 0x11B0C1: main (in /usr/bin/btrfs)
==883==
==883== Syscall param ioctl(generic) points to unaddressable byte(s)
==883==    at 0x4CA9CBB: ioctl (in /usr/lib/libc-2.29.so)
==883==    by 0x13C9AB: get_device_info (in /usr/bin/btrfs)
==883==    by 0x13D715: get_fs_info (in /usr/bin/btrfs)
==883==    by 0x153B5F: ??? (in /usr/bin/btrfs)
==883==    by 0x11B0C1: main (in /usr/bin/btrfs)
==883==  Address 0x4d8c7a0 is 0 bytes after a block of size 12,288 alloc'd
==883==    at 0x483877F: malloc (vg_replace_malloc.c:299)
==883==    by 0x13D861: get_fs_info (in /usr/bin/btrfs)
==883==    by 0x153B5F: ??? (in /usr/bin/btrfs)
==883==    by 0x11B0C1: main (in /usr/bin/btrfs)
==883==
--883-- VALGRIND INTERNAL ERROR: Valgrind received a signal 11 (SIGSEGV) - exiting
--883-- si_code=1;  Faulting address: 0x284D8C7B8;  sp: 0x1002eb5e50

valgrind: the 'impossible' happened:
   Killed by fatal signal

host stacktrace:
==883==    at 0x5805261C: get_bszB_as_is (m_mallocfree.c:303)
==883==    by 0x5805261C: get_bszB (m_mallocfree.c:315)
==883==    by 0x5805261C: vgPlain_arena_malloc (m_mallocfree.c:1799)
==883==    by 0x58005AD2: vgMemCheck_new_block (mc_malloc_wrappers.c:372)
==883==    by 0x58005AD2: vgMemCheck_malloc (mc_malloc_wrappers.c:407)
==883==    by 0x580A7373: do_client_request (scheduler.c:1925)
==883==    by 0x580A7373: vgPlain_scheduler (scheduler.c:1488)
==883==    by 0x580F57A0: thread_wrapper (syswrap-linux.c:103)
==883==    by 0x580F57A0: run_a_thread_NORETURN (syswrap-linux.c:156)

sched status:
  running_tid=1

Thread 1: status = VgTs_Runnable (lwpid 883)
==883==    at 0x483877F: malloc (vg_replace_malloc.c:299)
==883==    by 0x1534AA: ??? (in /usr/bin/btrfs)
==883==    by 0x153C49: ??? (in /usr/bin/btrfs)
==883==    by 0x11B0C1: main (in /usr/bin/btrfs)
client stack range: [0x1FFEFFA000 0x1FFF000FFF] client SP: 0x1FFEFFDCE0
valgrind stack range: [0x1002DB6000 0x1002EB5FFF] top usage: 7520 of 1048576

======================================================================

The above log says that invalid write to allocated @di_args happened
in get_device_info() called in get_fs_info().

The size of @di_args is allocated according by fi_args->num_devices.
And fi_args->num_devices is *the number of dev_items in chunk_tree*.
However, in the loop to get devices info, btrfs-progs calls ioctl
BTRFS_IOC_DEV_INFO which just finds device in
fs_info->fs_devices->devices.

Let's look at kernel side.
In btrfs_rm_device(), btrfs_rm_dev_item() causes removal of
related dev_items in chunk_tree. *Do something*.
Then delete the device from device->fs_devices.

So the case is:
Userspace					kernel

get_fs_info()					btrfs_rm_device()
						...
						  btrfs_rm_dev_item()

  determine fi_args->num_devices and
    fi_args->max_id by seraching chunk_tree.
  malloc()					  ...
  Loop(Crashed): call get_device_info() by devid
    from 1 to fi_args->max_id.
    	   					  mutex_lock(&fs_devices->device_list_mutex);
						  list_del_rcu(&device->dev_list);
					          ...

In the loop of get_device_info(), get_device_info() still can get info
of the removing device since it's still in fs_info->fs_devices->devices.
Then the iterator value @ndev increaments causes invalid access out of
bounds.

Solved it by adding the check of @ndev while looping.

Reported-by: Peter Hjalmarsson <kanelxake@gmail.com>
Link: https://bugzilla.redhat.com/show_bug.cgi?id=1711787
Signed-off-by: Su Yue <Damenly_Su@gmx.com>
---
 utils.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/utils.c b/utils.c
index c6cdc8f01dc1..0b271517551b 100644
--- a/utils.c
+++ b/utils.c
@@ -1763,7 +1763,8 @@ int get_fs_info(const char *path, struct btrfs_ioctl_fs_info_args *fi_args,
 
 	if (replacing)
 		memcpy(di_args, &tmp, sizeof(tmp));
-	for (; last_devid <= fi_args->max_id; last_devid++) {
+	for (; last_devid <= fi_args->max_id && ndevs < fi_args->num_devices;
+	     last_devid++) {
 		ret = get_device_info(fd, last_devid, &di_args[ndevs]);
 		if (ret == -ENODEV)
 			continue;
-- 
2.21.0


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