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| author | Cong Wang <xiyou.wangcong@gmail.com> | 2017-04-19 15:11:00 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2017-04-19 15:56:24 -0700 |
| commit | 073c516ff73557a8f7315066856c04b50383ac34 (patch) | |
| tree | eff12868fb4ddf3a3a60b695a1a8f95b873fe26e | |
| parent | 80d136e138f59de35aafb0440e8ab2f51c40ccd5 (diff) | |
| download | linux-073c516ff73557a8f7315066856c04b50383ac34.tar.bz2 | |
nsfs: mark dentry with DCACHE_RCUACCESS
Andrey reported a use-after-free in __ns_get_path():
spin_lock include/linux/spinlock.h:299 [inline]
lockref_get_not_dead+0x19/0x80 lib/lockref.c:179
__ns_get_path+0x197/0x860 fs/nsfs.c:66
open_related_ns+0xda/0x200 fs/nsfs.c:143
sock_ioctl+0x39d/0x440 net/socket.c:1001
vfs_ioctl fs/ioctl.c:45 [inline]
do_vfs_ioctl+0x1bf/0x1780 fs/ioctl.c:685
SYSC_ioctl fs/ioctl.c:700 [inline]
SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
We are under rcu read lock protection at that point:
rcu_read_lock();
d = atomic_long_read(&ns->stashed);
if (!d)
goto slow;
dentry = (struct dentry *)d;
if (!lockref_get_not_dead(&dentry->d_lockref))
goto slow;
rcu_read_unlock();
but don't use a proper RCU API on the free path, therefore a parallel
__d_free() could free it at the same time. We need to mark the stashed
dentry with DCACHE_RCUACCESS so that __d_free() will be called after all
readers leave RCU.
Fixes: e149ed2b805f ("take the targets of /proc/*/ns/* symlinks to separate fs")
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| -rw-r--r-- | fs/nsfs.c | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/fs/nsfs.c b/fs/nsfs.c index 1656843e87d2..323f492e0822 100644 --- a/fs/nsfs.c +++ b/fs/nsfs.c @@ -91,6 +91,7 @@ slow: return ERR_PTR(-ENOMEM); } d_instantiate(dentry, inode); + dentry->d_flags |= DCACHE_RCUACCESS; dentry->d_fsdata = (void *)ns->ops; d = atomic_long_cmpxchg(&ns->stashed, 0, (unsigned long)dentry); if (d) { |