4.16-stable review patch. If anyone has any objections, please let me know.
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From: Vivek Goyal vgoyal@redhat.com
commit 452061fd4521b2bf3225fc391dbe536e5f9c05e2 upstream.
d->last signifies that this is the last layer we are looking into and there is no more. And that means this allows for some optimzation opportunities during lookup. For example, in ovl_lookup_single() we don't have to check for opaque xattr of a directory is this is the last layer we are looking into (d->last = true).
But knowing for sure whether we are looking into last layer can be very tricky. If redirects are not enabled, then we can look at poe->numlower and figure out if the lookup we are about to is last layer or not. But if redircts are enabled then it is possible poe->numlower suggests that we are looking in last layer, but there is an absolute redirect present in found element and that redirects us to a layer in root and that means lookup will continue in lower layers further.
For example, consider following.
/upperdir/pure (opaque=y) /upperdir/pure/foo (opaque=y,redirect=/bar) /lowerdir/bar
In this case pure is "pure upper". When we look for "foo", that time poe->numlower=0. But that alone does not mean that we will not search for a merge candidate in /lowerdir. Absolute redirect changes that.
IOW, d->last should not be set just based on poe->numlower if redirects are enabled. That can lead to setting d->last while it should not have and that means we will not check for opaque xattr while we should have.
So do this.
- If redirects are not enabled, then continue to rely on poe->numlower information to determine if it is last layer or not.
- If redirects are enabled, then set d->last = true only if this is the last layer in root ovl_entry (roe).
Suggested-by: Amir Goldstein amir73il@gmail.com Reviewed-by: Amir Goldstein amir73il@gmail.com Signed-off-by: Vivek Goyal vgoyal@redhat.com Signed-off-by: Miklos Szeredi mszeredi@redhat.com Fixes: 02b69b284cd7 ("ovl: lookup redirects") Cc: stable@vger.kernel.org #v4.10 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/overlayfs/namei.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)
--- a/fs/overlayfs/namei.c +++ b/fs/overlayfs/namei.c @@ -815,7 +815,7 @@ struct dentry *ovl_lookup(struct inode * .is_dir = false, .opaque = false, .stop = false, - .last = !poe->numlower, + .last = ofs->config.redirect_follow ? false : !poe->numlower, .redirect = NULL, };
@@ -873,7 +873,11 @@ struct dentry *ovl_lookup(struct inode * for (i = 0; !d.stop && i < poe->numlower; i++) { struct ovl_path lower = poe->lowerstack[i];
- d.last = i == poe->numlower - 1; + if (!ofs->config.redirect_follow) + d.last = i == poe->numlower - 1; + else + d.last = lower.layer->idx == roe->numlower; + err = ovl_lookup_layer(lower.dentry, &d, &this); if (err) goto out_put;