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author | Hugh Dickins <hughd@google.com> | 2015-06-14 18:48:09 +0200 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2015-06-18 08:40:19 +0200 |
commit | 66fc13039422ba7df2d01a8ee0873e4ef965b50b (patch) | |
tree | 0826a86f9b90bf179b462e9d01b7887400a48ee0 /mm/shmem.c | |
parent | Linux 4.1-rc8 (diff) | |
download | linux-66fc13039422ba7df2d01a8ee0873e4ef965b50b.tar.xz linux-66fc13039422ba7df2d01a8ee0873e4ef965b50b.zip |
mm: shmem_zero_setup skip security check and lockdep conflict with XFS
It appears that, at some point last year, XFS made directory handling
changes which bring it into lockdep conflict with shmem_zero_setup():
it is surprising that mmap() can clone an inode while holding mmap_sem,
but that has been so for many years.
Since those few lockdep traces that I've seen all implicated selinux,
I'm hoping that we can use the __shmem_file_setup(,,,S_PRIVATE) which
v3.13's commit c7277090927a ("security: shmem: implement kernel private
shmem inodes") introduced to avoid LSM checks on kernel-internal inodes:
the mmap("/dev/zero") cloned inode is indeed a kernel-internal detail.
This also covers the !CONFIG_SHMEM use of ramfs to support /dev/zero
(and MAP_SHARED|MAP_ANONYMOUS). I thought there were also drivers
which cloned inode in mmap(), but if so, I cannot locate them now.
Reported-and-tested-by: Prarit Bhargava <prarit@redhat.com>
Reported-and-tested-by: Daniel Wagner <wagi@monom.org>
Reported-and-tested-by: Morten Stevens <mstevens@fedoraproject.org>
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/shmem.c')
-rw-r--r-- | mm/shmem.c | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/mm/shmem.c b/mm/shmem.c index de981370fbc5..47d536e59fc0 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -3401,7 +3401,13 @@ int shmem_zero_setup(struct vm_area_struct *vma) struct file *file; loff_t size = vma->vm_end - vma->vm_start; - file = shmem_file_setup("dev/zero", size, vma->vm_flags); + /* + * Cloning a new file under mmap_sem leads to a lock ordering conflict + * between XFS directory reading and selinux: since this file is only + * accessible to the user through its mapping, use S_PRIVATE flag to + * bypass file security, in the same way as shmem_kernel_file_setup(). + */ + file = __shmem_file_setup("dev/zero", size, vma->vm_flags, S_PRIVATE); if (IS_ERR(file)) return PTR_ERR(file); |