fs: Call d_automount with the filesystems creds
Seth Forshee reported a mount regression in nfs autmounts
with "fs: Add user namespace member to struct super_block".
It turns out that the assumption that current->cred is something
reasonable during mount while necessary to improve support of
unprivileged mounts is wrong in the automount path.
To fix the existing filesystems override current->cred with the
init_cred before calling d_automount and restore current->cred after
d_automount completes.
To support unprivileged mounts would require a more nuanced cred
selection, so fail on unprivileged mounts for the time being. As none
of the filesystems that currently set FS_USERNS_MOUNT implement
d_automount this check is only good for preventing future problems.
Fixes: 6e4eab577a
("fs: Add user namespace member to struct super_block")
Tested-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
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Коммит
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@ -36,6 +36,7 @@
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#include <linux/posix_acl.h>
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#include <linux/hash.h>
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#include <linux/bitops.h>
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#include <linux/init_task.h>
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#include <asm/uaccess.h>
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#include "internal.h"
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@ -1099,6 +1100,7 @@ static int follow_automount(struct path *path, struct nameidata *nd,
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bool *need_mntput)
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{
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struct vfsmount *mnt;
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const struct cred *old_cred;
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int err;
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if (!path->dentry->d_op || !path->dentry->d_op->d_automount)
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@ -1120,11 +1122,16 @@ static int follow_automount(struct path *path, struct nameidata *nd,
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path->dentry->d_inode)
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return -EISDIR;
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if (path->dentry->d_sb->s_user_ns != &init_user_ns)
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return -EACCES;
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nd->total_link_count++;
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if (nd->total_link_count >= 40)
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return -ELOOP;
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old_cred = override_creds(&init_cred);
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mnt = path->dentry->d_op->d_automount(path);
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revert_creds(old_cred);
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if (IS_ERR(mnt)) {
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/*
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* The filesystem is allowed to return -EISDIR here to indicate
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