Re: [PATCH] ovl: check dentry positiveness in ovl_cleanup_whiteouts()

From: Konstantin Khlebnikov
Date: Mon Nov 16 2015 - 11:26:21 EST

Note: kernels starting from 4.0 prints this
[ 72.925147] overlayfs: cleanup of '#ffff88022da16280/a' failed (-2)
instead of crashing, because of this part

--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -19,7 +19,7 @@ void ovl_cleanup(struct inode *wdir, struct dentry *wdentry)
int err;

- if (S_ISDIR(wdentry->d_inode->i_mode))
+ if (d_is_dir(wdentry))
err = ovl_do_rmdir(wdir, wdentry);
err = ovl_do_unlink(wdir, wdentry);

of e36cb0b89ce20b4f8786a57e8a6bc8476f577650
("VFS: (Scripted) Convert S_ISLNK/DIR/REG(dentry->d_inode) to d_is_*(dentry)")

in older kernels crash happens at dereferencing wdentry->d_inode
ovl_do_rmdir/unlink calls vfs_unlink/vfs_rmdir which checks positiveness
in may_delete(). both returns -ENOENT (-2) in that case.

So, patch is still required: at least for avoiding flood in kernel log.

On 16.11.2015 18:44, Konstantin Khlebnikov wrote:
This patch fixes kernel crash at removing directory which contains
whiteouts from lower layers.

Cache of directory content passed as "list" contains entries from all
layers, including whiteouts from lower layers. So, lookup in upper dir
(moved into work at this stage) will return negative entry. Plus this
cache is filled long before and we can race with external removal.

mkdir -p lower0/dir lower1/dir upper work overlay
touch lower0/dir/a lower0/dir/b
mknod lower1/dir/a c 0 0
mount -t overlay none overlay -o lowerdir=lower1:lower0,upperdir=upper,workdir=work
rm -fr overlay/dir

Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
Cc: Stable <stable@xxxxxxxxxxxxxxx> # 3.18+
fs/overlayfs/readdir.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
index 70e9af551600..adcb1398c481 100644
--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -571,7 +571,8 @@ void ovl_cleanup_whiteouts(struct dentry *upper, struct list_head *list)
(int) PTR_ERR(dentry));
- ovl_cleanup(upper->d_inode, dentry);
+ if (dentry->d_inode)
+ ovl_cleanup(upper->d_inode, dentry);

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