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| author | Al Viro <viro@zeniv.linux.org.uk> | 2016-06-07 21:26:55 -0400 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2016-06-24 10:15:29 -0700 |
| commit | 9db6c45bb3858dffba95afec2ccb8d05805cdff1 (patch) | |
| tree | 7a91467e74847add92d8f88691cbc3d317dd4262 | |
| parent | 8fa2337ec1643b52907bbcab51689a2c04557315 (diff) | |
| download | lwn-9db6c45bb3858dffba95afec2ccb8d05805cdff1.tar.gz lwn-9db6c45bb3858dffba95afec2ccb8d05805cdff1.zip | |
fix d_walk()/non-delayed __d_free() race
commit 3d56c25e3bb0726a5c5e16fc2d9e38f8ed763085 upstream.
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.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -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 9b235362efcd..47c06888dc05 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -1500,7 +1500,7 @@ 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 @@ -2352,7 +2352,6 @@ 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); } @@ -2536,6 +2535,7 @@ static void __d_move(struct dentry * dentry, struct dentry * target) /* ... and switch the parents */ if (IS_ROOT(dentry)) { + dentry->d_flags |= DCACHE_RCUACCESS; dentry->d_parent = target->d_parent; target->d_parent = target; INIT_LIST_HEAD(&target->d_child); |