From: Chengguang Xu cgxu519@mykernel.net
[ Upstream commit b71759ef1e1730db81dab98e9dab9455e8c7f5a2 ]
It is possible that a directory tree is shared between multiple overlay instances as a lower layer. In this case when one instance executes a file residing on the lower layer, the other instance denies a truncate(2) call on this file.
This only happens for truncate(2) and not for open(2) with the O_TRUNC flag.
Fix this interference and inconsistency by removing the preliminary i_writecount check before copy-up.
This means that unlike on normal filesystems truncate(argv[0]) will now succeed. If this ever causes a regression in a real world use case this needs to be revisited.
One way to fix this properly would be to keep a correct i_writecount in the overlay inode, but that is difficult due to memory mapping code only dealing with the real file/inode.
Signed-off-by: Chengguang Xu cgxu519@mykernel.net Signed-off-by: Miklos Szeredi mszeredi@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- Documentation/filesystems/overlayfs.rst | 3 +++ fs/overlayfs/inode.c | 6 ------ 2 files changed, 3 insertions(+), 6 deletions(-)
diff --git a/Documentation/filesystems/overlayfs.rst b/Documentation/filesystems/overlayfs.rst index 455ca86eb4fc..7da6c30ed596 100644 --- a/Documentation/filesystems/overlayfs.rst +++ b/Documentation/filesystems/overlayfs.rst @@ -427,6 +427,9 @@ b) If a file residing on a lower layer is opened for read-only and then memory mapped with MAP_SHARED, then subsequent changes to the file are not reflected in the memory mapping.
+c) If a file residing on a lower layer is being executed, then opening that +file for write or truncating the file will not be denied with ETXTBSY. + The following options allow overlayfs to act more like a standards compliant filesystem:
diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c index b288843e6b42..6566294c5fd6 100644 --- a/fs/overlayfs/inode.c +++ b/fs/overlayfs/inode.c @@ -33,12 +33,6 @@ int ovl_setattr(struct user_namespace *mnt_userns, struct dentry *dentry, goto out;
if (attr->ia_valid & ATTR_SIZE) { - struct inode *realinode = d_inode(ovl_dentry_real(dentry)); - - err = -ETXTBSY; - if (atomic_read(&realinode->i_writecount) < 0) - goto out_drop_write; - /* Truncate should trigger data copy up as well */ full_copy_up = true; }