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ovl: initialize ovl_copy_up_ctx.destname inside ovl_do_copy_up()

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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>
This commit is contained in:
Amir Goldstein 2023-11-20 15:43:34 +02:00
parent 02d70090e0
commit 2c3ef4f89c
1 changed files with 7 additions and 1 deletions
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8
fs/overlayfs/copy_up.c
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@ -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,