linux-toradex.git/ipc/shm.c, branch v4.4.103

ipc/shm: Fix shmat mmap nil-page protection

2017-03-12T05:37:26+00:00

commit 95e91b831f87ac8e1f8ed50c14d709089b4e01b8 upstream.

The issue is described here, with a nice testcase:

    https://bugzilla.kernel.org/show_bug.cgi?id=192931

The problem is that shmat() calls do_mmap_pgoff() with MAP_FIXED, and
the address rounded down to 0.  For the regular mmap case, the
protection mentioned above is that the kernel gets to generate the
address -- arch_get_unmapped_area() will always check for MAP_FIXED and
return that address.  So by the time we do security_mmap_addr(0) things
get funky for shmat().

The testcase itself shows that while a regular user crashes, root will
not have a problem attaching a nil-page.  There are two possible fixes
to this.  The first, and which this patch does, is to simply allow root
to crash as well -- this is also regular mmap behavior, ie when hacking
up the testcase and adding mmap(...  |MAP_FIXED).  While this approach
is the safer option, the second alternative is to ignore SHM_RND if the
rounded address is 0, thus only having MAP_SHARED flags.  This makes the
behavior of shmat() identical to the mmap() case.  The downside of this
is obviously user visible, but does make sense in that it maintains
semantics after the round-down wrt 0 address and mmap.

Passes shm related ltp tests.

Link: http://lkml.kernel.org/r/1486050195-18629-1-git-send-email-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso 
Reported-by: Gareth Evans 
Cc: Manfred Spraul 
Cc: Michael Kerrisk 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

ipc/shm: handle removed segments gracefully in shm_mmap()

2016-02-25T20:01:23+00:00

commit 1ac0b6dec656f3f78d1c3dd216fad84cb4d0a01e upstream.

remap_file_pages(2) emulation can reach file which represents removed
IPC ID as long as a memory segment is mapped.  It breaks expectations of
IPC subsystem.

Test case (rewritten to be more human readable, originally autogenerated
by syzkaller[1]):

	#define _GNU_SOURCE
	#include 
	#include 
	#include 
	#include 

	#define PAGE_SIZE 4096

	int main()
	{
		int id;
		void *p;

		id = shmget(IPC_PRIVATE, 3 * PAGE_SIZE, 0);
		p = shmat(id, NULL, 0);
		shmctl(id, IPC_RMID, NULL);
		remap_file_pages(p, 3 * PAGE_SIZE, 0, 7, 0);

	        return 0;
	}

The patch changes shm_mmap() and code around shm_lock() to propagate
locking error back to caller of shm_mmap().

[1] http://github.com/google/syzkaller

Signed-off-by: Kirill A. Shutemov 
Reported-by: Dmitry Vyukov 
Cc: Davidlohr Bueso 
Cc: Manfred Spraul 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

Initialize msg/shm IPC objects before doing ipc_addid()

2015-09-30T16:48:40+00:00

As reported by Dmitry Vyukov, we really shouldn't do ipc_addid() before
having initialized the IPC object state.  Yes, we initialize the IPC
object in a locked state, but with all the lockless RCU lookup work,
that IPC object lock no longer means that the state cannot be seen.

We already did this for the IPC semaphore code (see commit e8577d1f0329:
"ipc/sem.c: fully initialize sem_array before making it visible") but we
clearly forgot about msg and shm.

Reported-by: Dmitry Vyukov 
Cc: Manfred Spraul 
Cc: Davidlohr Bueso 
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds

ipc: convert invalid scenarios to use WARN_ON

2015-09-10T20:29:01+00:00

Considering Linus' past rants about the (ab)use of BUG in the kernel, I
took a look at how we deal with such calls in ipc.  Given that any errors
or corruption in ipc code are most likely contained within the set of
processes participating in the broken mechanisms, there aren't really many
strong fatal system failure scenarios that would require a BUG call.
Also, if something is seriously wrong, ipc might not be the place for such
a BUG either.

1. For example, recently, a customer hit one of these BUG_ONs in shm
   after failing shm_lock().  A busted ID imho does not merit a BUG_ON,
   and WARN would have been better.

2. MSG_COPY functionality of posix msgrcv(2) for checkpoint/restore.
   I don't see how we can hit this anyway -- at least it should be IS_ERR.
    The 'copy' arg from do_msgrcv is always set by calling prepare_copy()
   first and foremost.  We could also probably drop this check altogether.
    Either way, it does not merit a BUG_ON.

3. No ->fault() callback for the fs getting the corresponding page --
   seems selfish to make the system unusable.

Signed-off-by: Davidlohr Bueso 
Cc: Manfred Spraul 
Cc: Linus Torvalds 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

ipc: use private shmem or hugetlbfs inodes for shm segments.

2015-08-07T01:39:41+00:00

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:

  ======================================================
   [ INFO: possible circular locking dependency detected ]
   4.2.0-0.rc3.git0.1.fc24.x86_64+debug #1 Tainted: G        W
  -------------------------------------------------------
   httpd/1597 is trying to acquire lock:
   (&ids->rwsem){+++++.}, at: shm_close+0x34/0x130
   but task is already holding lock:
   (&mm->mmap_sem){++++++}, at: SyS_shmdt+0x4b/0x180
   which lock already depends on the new lock.
   the existing dependency chain (in reverse order) is:
   -> #3 (&mm->mmap_sem){++++++}:
        lock_acquire+0xc7/0x270
        __might_fault+0x7a/0xa0
        filldir+0x9e/0x130
        xfs_dir2_block_getdents.isra.12+0x198/0x1c0 [xfs]
        xfs_readdir+0x1b4/0x330 [xfs]
        xfs_file_readdir+0x2b/0x30 [xfs]
        iterate_dir+0x97/0x130
        SyS_getdents+0x91/0x120
        entry_SYSCALL_64_fastpath+0x12/0x76
   -> #2 (&xfs_dir_ilock_class){++++.+}:
        lock_acquire+0xc7/0x270
        down_read_nested+0x57/0xa0
        xfs_ilock+0x167/0x350 [xfs]
        xfs_ilock_attr_map_shared+0x38/0x50 [xfs]
        xfs_attr_get+0xbd/0x190 [xfs]
        xfs_xattr_get+0x3d/0x70 [xfs]
        generic_getxattr+0x4f/0x70
        inode_doinit_with_dentry+0x162/0x670
        sb_finish_set_opts+0xd9/0x230
        selinux_set_mnt_opts+0x35c/0x660
        superblock_doinit+0x77/0xf0
        delayed_superblock_init+0x10/0x20
        iterate_supers+0xb3/0x110
        selinux_complete_init+0x2f/0x40
        security_load_policy+0x103/0x600
        sel_write_load+0xc1/0x750
        __vfs_write+0x37/0x100
        vfs_write+0xa9/0x1a0
        SyS_write+0x58/0xd0
        entry_SYSCALL_64_fastpath+0x12/0x76
  ...

Signed-off-by: Stephen Smalley 
Reported-by: Morten Stevens 
Acked-by: Hugh Dickins 
Acked-by: Paul Moore 
Cc: Manfred Spraul 
Cc: Davidlohr Bueso 
Cc: Prarit Bhargava 
Cc: Eric Paris 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

ipc: rename ipc_obtain_object

2015-07-01T02:44:58+00:00

...  to ipc_obtain_object_idr, which is more meaningful and makes the code
slightly easier to follow.

Signed-off-by: Davidlohr Bueso 
Cc: Manfred Spraul 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

ipc,shm: move BUG_ON check into shm_lock

2015-07-01T02:44:58+00:00

Upon every shm_lock call, we BUG_ON if an error was returned, indicating
racing either in idr or in shm_destroy.  Move this logic into the locking.

[akpm@linux-foundation.org: simplify code]
Signed-off-by: Davidlohr Bueso 
Cc: Manfred Spraul 
Cc: Davidlohr Bueso 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

2015-04-27T00:22:07+00:00

Pull fourth vfs update from Al Viro:
 "d_inode() annotations from David Howells (sat in for-next since before
  the beginning of merge window) + four assorted fixes"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  RCU pathwalk breakage when running into a symlink overmounting something
  fix I_DIO_WAKEUP definition
  direct-io: only inc/dec inode->i_dio_count for file systems
  fs/9p: fix readdir()
  VFS: assorted d_backing_inode() annotations
  VFS: fs/inode.c helpers: d_inode() annotations
  VFS: fs/cachefiles: d_backing_inode() annotations
  VFS: fs library helpers: d_inode() annotations
  VFS: assorted weird filesystems: d_inode() annotations
  VFS: normal filesystems (and lustre): d_inode() annotations
  VFS: security/: d_inode() annotations
  VFS: security/: d_backing_inode() annotations
  VFS: net/: d_inode() annotations
  VFS: net/unix: d_backing_inode() annotations
  VFS: kernel/: d_inode() annotations
  VFS: audit: d_backing_inode() annotations
  VFS: Fix up some ->d_inode accesses in the chelsio driver
  VFS: Cachefiles should perform fs modifications on the top layer only
  VFS: AF_UNIX sockets should call mknod on the top layer only

ipc: remove use of seq_printf return value

2015-04-15T23:35:24+00:00

The seq_printf return value, because it's frequently misused,
will eventually be converted to void.

See: commit 1f33c41c03da ("seq_file: Rename seq_overflow() to
     seq_has_overflowed() and make public")

Signed-off-by: Joe Perches 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

VFS: assorted weird filesystems: d_inode() annotations

2015-04-15T19:06:58+00:00

Signed-off-by: David Howells 
Signed-off-by: Al Viro