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open: handle idmapped mounts in do_truncate()

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When truncating files the vfs will verify that the caller is privileged
over the inode. Extend it to handle idmapped mounts. If the inode is
accessed through an idmapped mount it is mapped according to the mount's
user namespace. Afterwards the permissions checks are identical to
non-idmapped mounts. If the initial user namespace is passed nothing
changes so non-idmapped mounts will see identical behavior as before.

Link: https://lore.kernel.org/r/20210121131959.646623-16-christian.brauner@ubuntu.com
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
This commit is contained in:
Christian Brauner
2021-01-21 14:19:34 +01:00
parent 6521f89170
commit 643fe55a06
5 changed files with 23 additions and 16 deletions
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7
fs/inode.c
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@@ -1903,7 +1903,8 @@ int dentry_needs_remove_privs(struct dentry *dentry)
return mask;
}
static int __remove_privs(struct dentry *dentry, int kill)
static int __remove_privs(struct user_namespace *mnt_userns,
struct dentry *dentry, int kill)
{
struct iattr newattrs;
@@ -1912,7 +1913,7 @@ static int __remove_privs(struct dentry *dentry, int kill)
* Note we call this on write, so notify_change will not
* encounter any conflicting delegations:
*/
return notify_change(&init_user_ns, dentry, &newattrs, NULL);
return notify_change(mnt_userns, dentry, &newattrs, NULL);
}
/*
@@ -1939,7 +1940,7 @@ int file_remove_privs(struct file *file)
if (kill < 0)
return kill;
if (kill)
error = __remove_privs(dentry, kill);
error = __remove_privs(file_mnt_user_ns(file), dentry, kill);
if (!error)
inode_has_no_xattr(inode);