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| author | Al Viro <viro@zeniv.linux.org.uk> | 2016-06-08 03:26:55 +0200 |
|---|---|---|
| committer | Al Viro <viro@zeniv.linux.org.uk> | 2016-06-08 03:26:55 +0200 |
| commit | 3d56c25e3bb0726a5c5e16fc2d9e38f8ed763085 (patch) | |
| tree | 3b76a5c52293cc900bd55a839831939a4ac47d44 /fs | |
| parent | autofs braino fix for do_last() (diff) | |
| download | linux-3d56c25e3bb0726a5c5e16fc2d9e38f8ed763085.tar.xz linux-3d56c25e3bb0726a5c5e16fc2d9e38f8ed763085.zip | |
fix d_walk()/non-delayed __d_free() race
Ascend-to-parent logics in d_walk() depends on all encountered child
dentries not getting freed without an RCU delay. Unfortunately, in
quite a few cases it is not true, with hard-to-hit oopsable race as
the result.
Fortunately, the fix is simiple; right now the rule is "if it ever
been hashed, freeing must be delayed" and changing it to "if it
ever had a parent, freeing must be delayed" closes that hole and
covers all cases the old rule used to cover. Moreover, pipes and
sockets remain _not_ covered, so we do not introduce RCU delay in
the cases which are the reason for having that delay conditional
in the first place.
Cc: stable@vger.kernel.org # v3.2+ (and watch out for __d_materialise_dentry())
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/dcache.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/fs/dcache.c b/fs/dcache.c index ad4a542e9bab..817c243c1ff1 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -1636,7 +1636,7 @@ struct dentry *d_alloc(struct dentry * parent, const struct qstr *name) struct dentry *dentry = __d_alloc(parent->d_sb, name); if (!dentry) return NULL; - + dentry->d_flags |= DCACHE_RCUACCESS; spin_lock(&parent->d_lock); /* * don't need child lock because it is not subject @@ -2358,7 +2358,6 @@ static void __d_rehash(struct dentry * entry, struct hlist_bl_head *b) { BUG_ON(!d_unhashed(entry)); hlist_bl_lock(b); - entry->d_flags |= DCACHE_RCUACCESS; hlist_bl_add_head_rcu(&entry->d_hash, b); hlist_bl_unlock(b); } @@ -2843,6 +2842,7 @@ static void __d_move(struct dentry *dentry, struct dentry *target, /* ... and switch them in the tree */ if (IS_ROOT(dentry)) { /* splicing a tree */ + dentry->d_flags |= DCACHE_RCUACCESS; dentry->d_parent = target->d_parent; target->d_parent = target; list_del_init(&target->d_child); |