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fuse: define the filesystem as untrusted

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Files on FUSE can change at any point in time without IMA being able
to detect it.  The file data read for the file signature verification
could be totally different from what is subsequently read, making the
signature verification useless.

FUSE can be mounted by unprivileged users either today with fusermount
installed with setuid, or soon with the upcoming patches to allow FUSE
mounts in a non-init user namespace.

This patch sets the SB_I_IMA_UNVERIFIABLE_SIGNATURE flag and when
appropriate sets the SB_I_UNTRUSTED_MOUNTER flag.

Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Seth Forshee <seth.forshee@canonical.com>
Cc: Dongsu Park <dongsu@kinvolk.io>
Cc: Alban Crequy <alban@kinvolk.io>
Acked-by: Serge Hallyn <serge@hallyn.com>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
Mimi Zohar 2018-02-21 11:36:52 -05:00
parent 9e67028e76
commit 0834136aea
1 changed files with 3 additions and 0 deletions
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3
fs/fuse/inode.c
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@ -1080,6 +1080,9 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent)
sb->s_maxbytes = MAX_LFS_FILESIZE; sb->s_maxbytes = MAX_LFS_FILESIZE;
sb->s_time_gran = 1; sb->s_time_gran = 1;
sb->s_export_op = &fuse_export_operations; sb->s_export_op = &fuse_export_operations;
sb->s_iflags |= SB_I_IMA_UNVERIFIABLE_SIGNATURE;
if (sb->s_user_ns != &init_user_ns)
sb->s_iflags |= SB_I_UNTRUSTED_MOUNTER;
file = fget(d.fd); file = fget(d.fd);
err = -EINVAL; err = -EINVAL;