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To support unprivileged users mounting filesystems two permission checks have to be performed: a test to see if the user allowed to create a mount in the mount namespace, and a test to see if the user is allowed to access the specified filesystem. The automount case is special in that mounting the original filesystem grants permission to mount the sub-filesystems, to any user who happens to stumble across the their mountpoint and satisfies the ordinary filesystem permission checks. Attempting to handle the automount case by using override_creds almost works. It preserves the idea that permission to mount the original filesystem is permission to mount the sub-filesystem. Unfortunately using override_creds messes up the filesystems ordinary permission checks. Solve this by being explicit that a mount is a submount by introducing vfs_submount, and using it where appropriate. vfs_submount uses a new mount internal mount flags MS_SUBMOUNT, to let sget and friends know that a mount is a submount so they can take appropriate action. sget and sget_userns are modified to not perform any permission checks on submounts. follow_automount is modified to stop using override_creds as that has proven problemantic. do_mount is modified to always remove the new MS_SUBMOUNT flag so that we know userspace will never by able to specify it. autofs4 is modified to stop using current_real_cred that was put in there to handle the previous version of submount permission checking. cifs is modified to pass the mountpoint all of the way down to vfs_submount. debugfs is modified to pass the mountpoint all of the way down to trace_automount by adding a new parameter. To make this change easier a new typedef debugfs_automount_t is introduced to capture the type of the debugfs automount function. Cc: stable@vger.kernel.org Fixes: |
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| .. | ||
| asn1.c | ||
| cache.c | ||
| cifs_debug.c | ||
| cifs_debug.h | ||
| cifs_dfs_ref.c | ||
| cifs_fs_sb.h | ||
| cifs_ioctl.h | ||
| cifs_spnego.c | ||
| cifs_spnego.h | ||
| cifs_unicode.c | ||
| cifs_unicode.h | ||
| cifs_uniupr.h | ||
| cifsacl.c | ||
| cifsacl.h | ||
| cifsencrypt.c | ||
| cifsfs.c | ||
| cifsfs.h | ||
| cifsglob.h | ||
| cifspdu.h | ||
| cifsproto.h | ||
| cifssmb.c | ||
| connect.c | ||
| dir.c | ||
| dns_resolve.c | ||
| dns_resolve.h | ||
| export.c | ||
| file.c | ||
| fscache.c | ||
| fscache.h | ||
| inode.c | ||
| ioctl.c | ||
| Kconfig | ||
| link.c | ||
| Makefile | ||
| misc.c | ||
| netmisc.c | ||
| nterr.c | ||
| nterr.h | ||
| ntlmssp.h | ||
| readdir.c | ||
| rfc1002pdu.h | ||
| sess.c | ||
| smb1ops.c | ||
| smb2file.c | ||
| smb2glob.h | ||
| smb2inode.c | ||
| smb2maperror.c | ||
| smb2misc.c | ||
| smb2ops.c | ||
| smb2pdu.c | ||
| smb2pdu.h | ||
| smb2proto.h | ||
| smb2status.h | ||
| smb2transport.c | ||
| smbencrypt.c | ||
| smberr.h | ||
| smbfsctl.h | ||
| transport.c | ||
| winucase.c | ||
| xattr.c | ||