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c1681bf8a7
struct block_device lifecycle is defined by its inode (see fs/block_dev.c) - block_device allocated first time we access /dev/loopXX and deallocated on bdev_destroy_inode. When we create the device "losetup /dev/loopXX afile" we want that block_device stay alive until we destroy the loop device with "losetup -d". But because we do not hold /dev/loopXX inode its counter goes 0, and inode/bdev can be destroyed at any moment. Usually it happens at memory pressure or when user drops inode cache (like in the test below). When later in loop_clr_fd() we want to use bdev we have use-after-free error with following stack: BUG: unable to handle kernel NULL pointer dereference at 0000000000000280 bd_set_size+0x10/0xa0 loop_clr_fd+0x1f8/0x420 [loop] lo_ioctl+0x200/0x7e0 [loop] lo_compat_ioctl+0x47/0xe0 [loop] compat_blkdev_ioctl+0x341/0x1290 do_filp_open+0x42/0xa0 compat_sys_ioctl+0xc1/0xf20 do_sys_open+0x16e/0x1d0 sysenter_dispatch+0x7/0x1a To prevent use-after-free we need to grab the device in loop_set_fd() and put it later in loop_clr_fd(). The issue is reprodusible on current Linus head and v3.3. Here is the test: dd if=/dev/zero of=loop.file bs=1M count=1 while [ true ]; do losetup /dev/loop0 loop.file echo 2 > /proc/sys/vm/drop_caches losetup -d /dev/loop0 done [ Doing bdgrab/bput in loop_set_fd/loop_clr_fd is safe, because every time we call loop_set_fd() we check that loop_device->lo_state is Lo_unbound and set it to Lo_bound If somebody will try to set_fd again it will get EBUSY. And if we try to loop_clr_fd() on unbound loop device we'll get ENXIO. loop_set_fd/loop_clr_fd (and any other loop ioctl) is called under loop_device->lo_ctl_mutex. ] Signed-off-by: Anatol Pomozov <anatol.pomozov@gmail.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
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aoe | ||
drbd | ||
mtip32xx | ||
paride | ||
rsxx | ||
xen-blkback | ||
amiflop.c | ||
ataflop.c | ||
brd.c | ||
cciss_cmd.h | ||
cciss_scsi.c | ||
cciss_scsi.h | ||
cciss.c | ||
cciss.h | ||
cpqarray.c | ||
cpqarray.h | ||
cryptoloop.c | ||
DAC960.c | ||
DAC960.h | ||
floppy.c | ||
hd.c | ||
ida_cmd.h | ||
ida_ioctl.h | ||
Kconfig | ||
loop.c | ||
Makefile | ||
mg_disk.c | ||
nbd.c | ||
nvme.c | ||
osdblk.c | ||
pktcdvd.c | ||
ps3disk.c | ||
ps3vram.c | ||
rbd_types.h | ||
rbd.c | ||
smart1,2.h | ||
sunvdc.c | ||
swim3.c | ||
swim_asm.S | ||
swim.c | ||
sx8.c | ||
umem.c | ||
umem.h | ||
virtio_blk.c | ||
xen-blkfront.c | ||
xsysace.c | ||
z2ram.c |