| Message ID | YCyx8u40HaplP7a+@mwanda (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | btrfs: prevent potential out of bounds in btrfs_ioctl_snap_create_v2() | expand |
On Wed, Feb 17, 2021 at 09:04:34AM +0300, Dan Carpenter wrote: > The problem is we're copying "inherit" from user space but we don't > necessarily know that we're copying enough data for a 64 byte > struct. Then the next problem is that "inherit" has a variable size > array at the end, and we have to verify that array is the size we > expected. > > Fixes: 6f72c7e20dba: ("Btrfs: add qgroup inheritance") > Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com> > --- > Presumably only root can create snapshots. Well, no. After first analysis there are some "interesting memory access patterns" possible, with a crafted data in the inherit member. > Anyway, I have not tested > this fix. I believe it is correct, of course. But perhaps it's best > to check. Yeah I'll write a test also to see where exactly the issues are. Thanks for the report/fix.
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c index 384d33ab02c7..9d7b24d3e3bd 100644 --- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c @@ -1941,15 +1941,34 @@ static noinline int btrfs_ioctl_snap_create_v2(struct file *file, if (vol_args->flags & BTRFS_SUBVOL_RDONLY) readonly = true; if (vol_args->flags & BTRFS_SUBVOL_QGROUP_INHERIT) { - if (vol_args->size > PAGE_SIZE) { + u64 nums; + + if (vol_args->size < sizeof(*inherit) || + vol_args->size > PAGE_SIZE) { ret = -EINVAL; goto free_args; } + inherit = memdup_user(vol_args->qgroup_inherit, vol_args->size); if (IS_ERR(inherit)) { ret = PTR_ERR(inherit); goto free_args; } + + /* quick and dirty checks to prevent integer overflows */ + if (inherit->num_qgroups > PAGE_SIZE || + inherit->num_ref_copies > PAGE_SIZE || + inherit->num_excl_copies > PAGE_SIZE) { + ret = -EINVAL; + goto free_inherit; + } + + nums = inherit->num_qgroups + 2 * inherit->num_ref_copies + + 2 * inherit->num_excl_copies; + if (vol_args->size != struct_size(inherit, qgroups, nums)) { + ret = -EINVAL; + goto free_inherit; + } } ret = __btrfs_ioctl_snap_create(file, vol_args->name, vol_args->fd,
The problem is we're copying "inherit" from user space but we don't necessarily know that we're copying enough data for a 64 byte struct. Then the next problem is that "inherit" has a variable size array at the end, and we have to verify that array is the size we expected. Fixes: 6f72c7e20dba: ("Btrfs: add qgroup inheritance") Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com> --- Presumably only root can create snapshots. Anyway, I have not tested this fix. I believe it is correct, of course. But perhaps it's best to check. The calculation for the number of elements in the array was copied from btrfs_qgroup_inherit(). fs/btrfs/ioctl.c | 21 ++++++++++++++++++++- 1 file changed, 20 insertions(+), 1 deletion(-)