From: Miklos Szeredi Date: Tue, 29 Nov 2016 09:20:24 +0000 (+0100) Subject: ovl: fix d_real() for stacked fs X-Git-Tag: v4.9.8~879^2 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=c4fcfc1619ea43a8a89ad2f83ff23905eee088bd;p=platform%2Fkernel%2Flinux-rpi3.git ovl: fix d_real() for stacked fs Handling of recursion in d_real() is completely broken. Recursion is only done in the 'inode != NULL' case. But when opening the file we have 'inode == NULL' hence d_real() will return an overlay dentry. This won't work since overlayfs doesn't define its own file operations, so all file ops will fail. Fix by doing the recursion first and the check against the inode second. Bash script to reproduce the issue written by Quentin: - 8< - - - - - 8< - - - - - 8< - - - - - 8< - - - - tmpdir=$(mktemp -d) pushd ${tmpdir} mkdir -p {upper,lower,work} echo -n 'rocks' > lower/ksplice mount -t overlay level_zero upper -o lowerdir=lower,upperdir=upper,workdir=work cat upper/ksplice tmpdir2=$(mktemp -d) pushd ${tmpdir2} mkdir -p {upper,work} mount -t overlay level_one upper -o lowerdir=${tmpdir}/upper,upperdir=upper,workdir=work ls -l upper/ksplice cat upper/ksplice - 8< - - - - - 8< - - - - - 8< - - - - - 8< - - - - Reported-by: Quentin Casasnovas Signed-off-by: Miklos Szeredi Fixes: 2d902671ce1c ("vfs: merge .d_select_inode() into .d_real()") Cc: # v4.8+ --- diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c index edd46a0..0e10085 100644 --- a/fs/overlayfs/super.c +++ b/fs/overlayfs/super.c @@ -328,11 +328,11 @@ static struct dentry *ovl_d_real(struct dentry *dentry, if (!real) goto bug; + /* Handle recursion */ + real = d_real(real, inode, open_flags); + if (!inode || inode == d_inode(real)) return real; - - /* Handle recursion */ - return d_real(real, inode, open_flags); bug: WARN(1, "ovl_d_real(%pd4, %s:%lu): real dentry not found\n", dentry, inode ? inode->i_sb->s_id : "NULL", inode ? inode->i_ino : 0);