URL: https://bugzilla.kernel.org/show_bug.cgi?id=97041
 Lukas Lueg 2015-04-21 21:53:14 UTC

The btrfs-image attached to this bug causes the userland tools v3.19.1 to
crash with a SIGFPE. The problem is that map->sub_stripes in
__btrfs_map_block() is allowed to be 0 before entering a division.

The userland tool crashes. The kernel reports a "divide error: 0000 ..."
with a traceback from __btrfs_map_block()


(gdb) run check btrfs_fukked_sigfpe_volumes:1404.bin
Starting program: /usr/sbin/btrfs check btrfs_fukked_sigfpe_volumes:1404.bin
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".

Program received signal SIGFPE, Arithmetic exception.
0x000000000044d7b6 in __btrfs_map_block (map_tree=map_tree@entry=0x88c170, 
    rw=rw@entry=0, logical=<optimized out>, length=length@entry=0x7fffffffd8f0, 
    type=type@entry=0x0, multi_ret=multi_ret@entry=0x7fffffffd8e8, mirror_num=0, 
    raid_map_ret=0x0) at volumes.c:1404
1404			int factor = map->num_stripes / map->sub_stripes;
(gdb) bt
#0  0x000000000044d7b6 in __btrfs_map_block (map_tree=map_tree@entry=0x88c170, 
    rw=rw@entry=0, logical=<optimized out>, length=length@entry=0x7fffffffd8f0, 
    type=type@entry=0x0, multi_ret=multi_ret@entry=0x7fffffffd8e8, mirror_num=0, 
    raid_map_ret=0x0) at volumes.c:1404
#1  0x000000000044db45 in btrfs_map_block (map_tree=map_tree@entry=0x88c170, 
    rw=rw@entry=0, logical=<optimized out>, length=length@entry=0x7fffffffd8f0, 
    multi_ret=multi_ret@entry=0x7fffffffd8e8, mirror_num=mirror_num@entry=0, 
    raid_map_ret=0x0) at volumes.c:1291
#2  0x000000000043b22d in read_whole_eb (info=0x88c010, eb=eb@entry=0x88f400, 
    mirror=mirror@entry=0) at disk-io.c:232
#3  0x000000000043caa2 in read_tree_block (root=root@entry=0x88c710, 
    bytenr=<optimized out>, blocksize=<optimized out>, parent_transid=5)
    at disk-io.c:295
#4  0x000000000043d5df in btrfs_setup_chunk_tree_and_device_map (
    fs_info=fs_info@entry=0x88c010) at disk-io.c:1106
#5  0x000000000043d7d1 in __open_ctree_fd (fp=fp@entry=3, 
    path=path@entry=0x7fffffffe1fa "btrfs_fukked_sigfpe_volumes:1404.bin", 
    sb_bytenr=65536, sb_bytenr@entry=0, root_tree_bytenr=root_tree_bytenr@entry=0, 
    flags=flags@entry=OPEN_CTREE_EXCLUSIVE) at disk-io.c:1190
#6  0x000000000043d965 in open_ctree_fs_info (
    filename=0x7fffffffe1fa "btrfs_fukked_sigfpe_volumes:1404.bin", 
    sb_bytenr=sb_bytenr@entry=0, root_tree_bytenr=root_tree_bytenr@entry=0, 
    flags=flags@entry=OPEN_CTREE_EXCLUSIVE) at disk-io.c:1231
#7  0x0000000000427bf5 in cmd_check (argc=1, argv=0x7fffffffde90) at cmds-check.c:9326
#8  0x000000000040e5a2 in main (argc=2, argv=0x7fffffffde90) at btrfs.c:245
(gdb) p map->sub_stripes
$1 = 0