RCU pathwalk breakage when running into a symlink overmounting something
Calling unlazy_walk() in walk_component() and do_last() when we find a symlink that needs to be followed doesn't acquire a reference to vfsmount. That's fine when the symlink is on the same vfsmount as the parent directory (which is almost always the case), but it's not always true - one _can_ manage to bind a symlink on top of something. And in such cases we end up with excessive mntput(). Cc: stable@vger.kernel.org # since 2.6.39 Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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@ -1590,7 +1590,8 @@ static inline int walk_component(struct nameidata *nd, struct path *path,
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if (should_follow_link(path->dentry, follow)) {
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if (should_follow_link(path->dentry, follow)) {
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if (nd->flags & LOOKUP_RCU) {
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if (nd->flags & LOOKUP_RCU) {
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if (unlikely(unlazy_walk(nd, path->dentry))) {
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if (unlikely(nd->path.mnt != path->mnt ||
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unlazy_walk(nd, path->dentry))) {
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err = -ECHILD;
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err = -ECHILD;
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goto out_err;
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goto out_err;
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}
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}
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@ -3045,7 +3046,8 @@ finish_lookup:
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if (should_follow_link(path->dentry, !symlink_ok)) {
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if (should_follow_link(path->dentry, !symlink_ok)) {
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if (nd->flags & LOOKUP_RCU) {
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if (nd->flags & LOOKUP_RCU) {
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if (unlikely(unlazy_walk(nd, path->dentry))) {
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if (unlikely(nd->path.mnt != path->mnt ||
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unlazy_walk(nd, path->dentry))) {
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error = -ECHILD;
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error = -ECHILD;
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goto out;
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goto out;
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}
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}
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