From: Amir Goldstein <amir73il@gmail.com>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: Al Viro <viro@zeniv.linux.org.uk>, linux-unionfs@vger.kernel.org
Subject: [PATCH] ovl: initialize ovl_copy_up_ctx.destname inside ovl_do_copy_up()
Date: Mon, 20 Nov 2023 16:00:38 +0200 [thread overview]
Message-ID: <20231120140038.2211224-1-amir73il@gmail.com> (raw)
The ->destname member of struct ovl_copy_up_ctx is initialized inside
ovl_copy_up_one() to ->d_name of the overlayfs dentry being copied up
and then it may be overridden by index name inside ovl_do_copy_up().
ovl_inode_lock() in ovl_copy_up_start() and ovl_copy_up() in ovl_rename()
effectively stabilze ->d_name of the overlayfs dentry being copied up,
but ovl_inode_lock() is not held when ->d_name is being read.
It is not a correctness bug, because if ovl_do_copy_up() races with
ovl_rename() and ctx.destname is freed, we will not end up calling
ovl_do_copy_up() with the dead name reference.
The code becomes much easier to understand and to document if the
initialization of c->destname is always done inside ovl_do_copy_up(),
either to the index entry name, or to the overlay dentry ->d_name.
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
fs/overlayfs/copy_up.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
index 4382881b0709..500c555792ff 100644
--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -929,6 +929,13 @@ static int ovl_do_copy_up(struct ovl_copy_up_ctx *c)
err = -EIO;
goto out_free_fh;
} else {
+ /*
+ * c->dentry->d_name is stabilzed by ovl_copy_up_start(),
+ * because if we got here, it means that c->dentry has no upper
+ * alias and changing ->d_name means going through ovl_rename()
+ * that will call ovl_copy_up() on source and target dentry.
+ */
+ c->destname = c->dentry->d_name;
/*
* Mark parent "impure" because it may now contain non-pure
* upper
@@ -1109,7 +1116,6 @@ static int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry,
if (parent) {
ovl_path_upper(parent, &parentpath);
ctx.destdir = parentpath.dentry;
- ctx.destname = dentry->d_name;
err = vfs_getattr(&parentpath, &ctx.pstat,
STATX_ATIME | STATX_MTIME,
--
2.34.1
reply other threads:[~2023-11-20 14:00 UTC|newest]
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