[PATCH v2] ipc: Use private shmem or hugetlbfs inodes for shm segments.

From: Stephen Smalley
Date: Fri Jul 24 2015 - 08:36:28 EST

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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(-)

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

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Next message: Krzysztof Kozlowski: "Re: [PATCH] power_supply: Adjust devm usage"
Previous message: Vaishali Thakkar: "Re: [PATCH] power_supply: Adjust devm usage"
Next in thread: Paul Moore: "Re: [PATCH v2] ipc: Use private shmem or hugetlbfs inodes for shm segments."
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