回复:[PATCH] ovl: check VM_DENYWRITE mappings in copy-up

[Chengguang Xu <cgxu519@mykernel.net>]

 ---- 在 星期四, 2021-04-08 19:20:42 Chengguang Xu <cgxu519@mykernel.net> 撰写 ----
 > In overlayfs copy-up, if open flag has O_TRUNC then upper
 > file will truncate to zero size, in this case we should check
 > VM_DENYWRITE mappings to keep compatibility with other filesystems.
 > 
 > Signed-off-by: Chengguang Xu <cgxu519@mykernel.net>
 > ---
 >  fs/overlayfs/copy_up.c | 5 ++++-
 >  1 file changed, 4 insertions(+), 1 deletion(-)
 > 
 > diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
 > index 0fed532efa68..c56c81494b0c 100644
 > --- a/fs/overlayfs/copy_up.c
 > +++ b/fs/overlayfs/copy_up.c
 > @@ -901,8 +901,11 @@ static int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry,
 >      }
 >  
 >      /* maybe truncate regular file. this has no effect on dirs */
 > -    if (flags & O_TRUNC)
 > +    if (flags & O_TRUNC) {
 > +        if (atomic_read(&d_inode(ovl_dentry_real(dentry))->i_writecount) < 0)
 > +            return -ETXTBSY;
 >          ctx.stat.size = 0;
 > +    }

Maybe we should check this for open(with writable flag) not only for truncate case, right?


Thanks,
Chengguang


 >  
 >      if (S_ISLNK(ctx.stat.mode)) {
 >          ctx.link = vfs_get_link(ctx.lowerpath.dentry, &done);
 > -- 
 > 2.27.0
 > 
 > 
 >