On Fri, Jul 24, 2015 at 8:34 AM, Stephen Smalley <sds@xxxxxxxxxxxxx> wrote:
> The shm implementation internally uses shmem or hugetlbfs inodes
> for shm segments. As these inodes are never directly exposed to
> userspace and only accessed through the shm operations which are
> already hooked by security modules, mark the inodes with the
> S_PRIVATE flag so that inode security initialization and permission
> checking is skipped.
>
> This was motivated by the following lockdep warning:
> Jul 22 14:36:40 fc23 kernel:
> ======================================================
> Jul 22 14:36:40 fc23 kernel: [ INFO: possible circular locking
> dependency detected ]
> Jul 22 14:36:40 fc23 kernel: 4.2.0-0.rc3.git0.1.fc24.x86_64+debug #1
> Tainted: G W
> Jul 22 14:36:40 fc23 kernel:
> -------------------------------------------------------
> Jul 22 14:36:40 fc23 kernel: httpd/1597 is trying to acquire lock:
> Jul 22 14:36:40 fc23 kernel: (&ids->rwsem){+++++.}, at:
> [<ffffffff81385354>] shm_close+0x34/0x130
> Jul 22 14:36:40 fc23 kernel: #012but task is already holding lock:
> Jul 22 14:36:40 fc23 kernel: (&mm->mmap_sem){++++++}, at:
> [<ffffffff81386bbb>] SyS_shmdt+0x4b/0x180
> Jul 22 14:36:40 fc23 kernel: #012which lock already depends on the new lock.
> Jul 22 14:36:40 fc23 kernel: #012the existing dependency chain (in
> reverse order) is:
> Jul 22 14:36:40 fc23 kernel: #012-> #3 (&mm->mmap_sem){++++++}:
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81109a07>] lock_acquire+0xc7/0x270
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81217baa>] __might_fault+0x7a/0xa0
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81284a1e>] filldir+0x9e/0x130
> Jul 22 14:36:40 fc23 kernel: [<ffffffffa019bb08>]
> xfs_dir2_block_getdents.isra.12+0x198/0x1c0 [xfs]
> Jul 22 14:36:40 fc23 kernel: [<ffffffffa019c5b4>]
> xfs_readdir+0x1b4/0x330 [xfs]
> Jul 22 14:36:40 fc23 kernel: [<ffffffffa019f38b>]
> xfs_file_readdir+0x2b/0x30 [xfs]
> Jul 22 14:36:40 fc23 kernel: [<ffffffff812847e7>] iterate_dir+0x97/0x130
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81284d21>] SyS_getdents+0x91/0x120
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81871d2e>]
> entry_SYSCALL_64_fastpath+0x12/0x76
> Jul 22 14:36:40 fc23 kernel: #012-> #2 (&xfs_dir_ilock_class){++++.+}:
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81109a07>] lock_acquire+0xc7/0x270
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81101e97>]
> down_read_nested+0x57/0xa0
> Jul 22 14:36:40 fc23 kernel: [<ffffffffa01b0e57>]
> xfs_ilock+0x167/0x350 [xfs]
> Jul 22 14:36:40 fc23 kernel: [<ffffffffa01b10b8>]
> xfs_ilock_attr_map_shared+0x38/0x50 [xfs]
> Jul 22 14:36:40 fc23 kernel: [<ffffffffa014799d>]
> xfs_attr_get+0xbd/0x190 [xfs]
> Jul 22 14:36:40 fc23 kernel: [<ffffffffa01c17ad>]
> xfs_xattr_get+0x3d/0x70 [xfs]
> Jul 22 14:36:40 fc23 kernel: [<ffffffff8129962f>]
> generic_getxattr+0x4f/0x70
> Jul 22 14:36:40 fc23 kernel: [<ffffffff8139ba52>]
> inode_doinit_with_dentry+0x162/0x670
> Jul 22 14:36:40 fc23 kernel: [<ffffffff8139cf69>]
> sb_finish_set_opts+0xd9/0x230
> Jul 22 14:36:40 fc23 kernel: [<ffffffff8139d66c>]
> selinux_set_mnt_opts+0x35c/0x660
> Jul 22 14:36:40 fc23 kernel: [<ffffffff8139ff97>]
> superblock_doinit+0x77/0xf0
> Jul 22 14:36:40 fc23 kernel: [<ffffffff813a0020>]
> delayed_superblock_init+0x10/0x20
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81272d23>]
> iterate_supers+0xb3/0x110
> Jul 22 14:36:40 fc23 kernel: [<ffffffff813a4e5f>]
> selinux_complete_init+0x2f/0x40
> Jul 22 14:36:40 fc23 kernel: [<ffffffff813b47a3>]
> security_load_policy+0x103/0x600
> Jul 22 14:36:40 fc23 kernel: [<ffffffff813a6901>]
> sel_write_load+0xc1/0x750
> Jul 22 14:36:40 fc23 kernel: [<ffffffff8126e817>] __vfs_write+0x37/0x100
> Jul 22 14:36:40 fc23 kernel: [<ffffffff8126f229>] vfs_write+0xa9/0x1a0
> Jul 22 14:36:40 fc23 kernel: [<ffffffff8126ff48>] SyS_write+0x58/0xd0
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81871d2e>]
> entry_SYSCALL_64_fastpath+0x12/0x76
> Jul 22 14:36:40 fc23 kernel: #012-> #1 (&isec->lock){+.+.+.}:
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81109a07>] lock_acquire+0xc7/0x270
> Jul 22 14:36:40 fc23 kernel: [<ffffffff8186de8f>]
> mutex_lock_nested+0x7f/0x3e0
> Jul 22 14:36:40 fc23 kernel: [<ffffffff8139b9a9>]
> inode_doinit_with_dentry+0xb9/0x670
> Jul 22 14:36:40 fc23 kernel: [<ffffffff8139bf7c>]
> selinux_d_instantiate+0x1c/0x20
> Jul 22 14:36:40 fc23 kernel: [<ffffffff813955f6>]
> security_d_instantiate+0x36/0x60
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81287c34>] d_instantiate+0x54/0x70
> Jul 22 14:36:40 fc23 kernel: [<ffffffff8120111c>]
> __shmem_file_setup+0xdc/0x240
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81201290>]
> shmem_file_setup+0x10/0x20
> Jul 22 14:36:40 fc23 kernel: [<ffffffff813856e0>] newseg+0x290/0x3a0
> Jul 22 14:36:40 fc23 kernel: [<ffffffff8137e278>] ipcget+0x208/0x2d0
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81386074>] SyS_shmget+0x54/0x70
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81871d2e>]
> entry_SYSCALL_64_fastpath+0x12/0x76
> Jul 22 14:36:40 fc23 kernel: #012-> #0 (&ids->rwsem){+++++.}:
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81108df8>]
> __lock_acquire+0x1a78/0x1d00
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81109a07>] lock_acquire+0xc7/0x270
> Jul 22 14:36:40 fc23 kernel: [<ffffffff8186efba>] down_write+0x5a/0xc0
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81385354>] shm_close+0x34/0x130
> Jul 22 14:36:40 fc23 kernel: [<ffffffff812203a5>] remove_vma+0x45/0x80
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81222a30>] do_munmap+0x2b0/0x460
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81386c25>] SyS_shmdt+0xb5/0x180
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81871d2e>]
> entry_SYSCALL_64_fastpath+0x12/0x76
> Jul 22 14:36:40 fc23 kernel: #012other info that might help us debug this:
> Jul 22 14:36:40 fc23 kernel: Chain exists of:#012 &ids->rwsem -->
> &xfs_dir_ilock_class --> &mm->mmap_sem
> Jul 22 14:36:40 fc23 kernel: Possible unsafe locking scenario:
> Jul 22 14:36:40 fc23 kernel: CPU0 CPU1
> Jul 22 14:36:40 fc23 kernel: ---- ----
> Jul 22 14:36:40 fc23 kernel: lock(&mm->mmap_sem);
> Jul 22 14:36:40 fc23 kernel:
> lock(&xfs_dir_ilock_class);
> Jul 22 14:36:40 fc23 kernel: lock(&mm->mmap_sem);
> Jul 22 14:36:40 fc23 kernel: lock(&ids->rwsem);
> Jul 22 14:36:40 fc23 kernel: #012 *** DEADLOCK ***
> Jul 22 14:36:40 fc23 kernel: 1 lock held by httpd/1597:
> Jul 22 14:36:40 fc23 kernel: #0: (&mm->mmap_sem){++++++}, at:
> [<ffffffff81386bbb>] SyS_shmdt+0x4b/0x180
> Jul 22 14:36:40 fc23 kernel: #012stack backtrace:
> Jul 22 14:36:40 fc23 kernel: CPU: 7 PID: 1597 Comm: httpd Tainted: G
> W 4.2.0-0.rc3.git0.1.fc24.x86_64+debug #1
> Jul 22 14:36:40 fc23 kernel: Hardware name: VMware, Inc. VMware
> Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00
> 05/20/2014
> Jul 22 14:36:40 fc23 kernel: 0000000000000000 000000006cb6fe9d
> ffff88019ff07c58 ffffffff81868175
> Jul 22 14:36:40 fc23 kernel: 0000000000000000 ffffffff82aea390
> ffff88019ff07ca8 ffffffff81105903
> Jul 22 14:36:40 fc23 kernel: ffff88019ff07c78 ffff88019ff07d08
> 0000000000000001 ffff8800b75108f0
> Jul 22 14:36:40 fc23 kernel: Call Trace:
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81868175>] dump_stack+0x4c/0x65
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81105903>] print_circular_bug+0x1e3/0x250
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81108df8>] __lock_acquire+0x1a78/0x1d00
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81220c33>] ? unlink_file_vma+0x33/0x60
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81109a07>] lock_acquire+0xc7/0x270
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81385354>] ? shm_close+0x34/0x130
> Jul 22 14:36:40 fc23 kernel: [<ffffffff8186efba>] down_write+0x5a/0xc0
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81385354>] ? shm_close+0x34/0x130
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81385354>] shm_close+0x34/0x130
> Jul 22 14:36:40 fc23 kernel: [<ffffffff812203a5>] remove_vma+0x45/0x80
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81222a30>] do_munmap+0x2b0/0x460
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81386bbb>] ? SyS_shmdt+0x4b/0x180
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81386c25>] SyS_shmdt+0xb5/0x180
> Jul 22 14:36:40 fc23 kernel: [<ffffffff81871d2e>]
> entry_SYSCALL_64_fastpath+0x12/0x76
>
> Reported-by: Morten Stevens <mstevens@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Stephen Smalley <sds@xxxxxxxxxxxxx>
> ---
> This version only differs in the patch description, which restores
> the original lockdep trace from Morten Stevens. It was unfortunately
> mangled in the prior version.
>
> fs/hugetlbfs/inode.c | 2 ++
> ipc/shm.c | 2 +-
> mm/shmem.c | 4 ++--
> 3 files changed, 5 insertions(+), 3 deletions(-)
The stuff below looked reasonable to me yesterday, still looks reasonable today.
Acked-by: Paul Moore <paul@xxxxxxxxxxxxxx>
> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
> index 0cf74df..973c24c 100644
> --- a/fs/hugetlbfs/inode.c
> +++ b/fs/hugetlbfs/inode.c
> @@ -1010,6 +1010,8 @@ struct file *hugetlb_file_setup(const char *name, size_t size,
> inode = hugetlbfs_get_inode(sb, NULL, S_IFREG | S_IRWXUGO, 0);
> if (!inode)
> goto out_dentry;
> + if (creat_flags == HUGETLB_SHMFS_INODE)
> + inode->i_flags |= S_PRIVATE;
>
> file = ERR_PTR(-ENOMEM);
> if (hugetlb_reserve_pages(inode, 0,
> diff --git a/ipc/shm.c b/ipc/shm.c
> index 06e5cf2..4aef24d 100644
> --- a/ipc/shm.c
> +++ b/ipc/shm.c
> @@ -545,7 +545,7 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
> if ((shmflg & SHM_NORESERVE) &&
> sysctl_overcommit_memory != OVERCOMMIT_NEVER)
> acctflag = VM_NORESERVE;
> - file = shmem_file_setup(name, size, acctflag);
> + file = shmem_kernel_file_setup(name, size, acctflag);
> }
> error = PTR_ERR(file);
> if (IS_ERR(file))
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 4caf8ed..dbe0c1e 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -3363,8 +3363,8 @@ put_path:
> * shmem_kernel_file_setup - get an unlinked file living in tmpfs which must be
> * kernel internal. There will be NO LSM permission checks against the
> * underlying inode. So users of this interface must do LSM checks at a
> - * higher layer. The one user is the big_key implementation. LSM checks
> - * are provided at the key level rather than the inode level.
> + * higher layer. The users are the big_key and shm implementations. LSM
> + * checks are provided at the key or shm level rather than the inode.
> * @name: name for dentry (to be seen in /proc/<pid>/maps
> * @size: size to be set for the file
> * @flags: VM_NORESERVE suppresses pre-accounting of the entire object size
> --
> 2.1.0
>
--
paul moore
www.paul-moore.com
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