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authorCong Wang <xiyou.wangcong@gmail.com>2017-04-19 15:11:00 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2017-04-19 15:56:24 -0700
commit073c516ff73557a8f7315066856c04b50383ac34 (patch)
parent80d136e138f59de35aafb0440e8ab2f51c40ccd5 (diff)
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>
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) {