Revision 1e9c75fb9c47a75a9aec0cd17db5f6dc36b58e00 authored by Benjamin Coddington on 03 October 2018, 14:18:33 UTC, committed by Eric W. Biederman on 12 November 2018, 07:02:34 UTC
Since commit ff17fa561a04 ("d_invalidate(): unhash immediately")
immediately unhashes the dentry, we'll never return the mountpoint in
lookup_mountpoint(), which can lead to an unbreakable loop in
d_invalidate().
I have reports of NFS clients getting into this condition after the server
removes an export of an existing mount created through follow_automount(),
but I suspect there are various other ways to produce this problem if we
hunt down users of d_invalidate(). For example, it is possible to get into
this state by using XFS' d_invalidate() call in xfs_vn_unlink():
truncate -s 100m img{1,2}
mkfs.xfs -q -n version=ci img1
mkfs.xfs -q -n version=ci img2
mkdir -p /mnt/xfs
mount img1 /mnt/xfs
mkdir /mnt/xfs/sub1
mount img2 /mnt/xfs/sub1
cat > /mnt/xfs/sub1/foo &
umount -l /mnt/xfs/sub1
mount img2 /mnt/xfs/sub1
mount --make-private /mnt/xfs
mkdir /mnt/xfs/sub2
mount --move /mnt/xfs/sub1 /mnt/xfs/sub2
rmdir /mnt/xfs/sub1
Fix this by moving the check for an unlinked dentry out of the
detach_mounts() path.
Fixes: ff17fa561a04 ("d_invalidate(): unhash immediately")
Cc: stable@vger.kernel.org
Reviewed-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
1 parent 9c8e0a1
Kconfig
# SPDX-License-Identifier: GPL-2.0
menu "Certificates for signature checking"
config MODULE_SIG_KEY
string "File name or PKCS#11 URI of module signing key"
default "certs/signing_key.pem"
depends on MODULE_SIG
help
Provide the file name of a private key/certificate in PEM format,
or a PKCS#11 URI according to RFC7512. The file should contain, or
the URI should identify, both the certificate and its corresponding
private key.
If this option is unchanged from its default "certs/signing_key.pem",
then the kernel will automatically generate the private key and
certificate as described in Documentation/admin-guide/module-signing.rst
config SYSTEM_TRUSTED_KEYRING
bool "Provide system-wide ring of trusted keys"
depends on KEYS
depends on ASYMMETRIC_KEY_TYPE
help
Provide a system keyring to which trusted keys can be added. Keys in
the keyring are considered to be trusted. Keys may be added at will
by the kernel from compiled-in data and from hardware key stores, but
userspace may only add extra keys if those keys can be verified by
keys already in the keyring.
Keys in this keyring are used by module signature checking.
config SYSTEM_TRUSTED_KEYS
string "Additional X.509 keys for default system keyring"
depends on SYSTEM_TRUSTED_KEYRING
help
If set, this option should be the filename of a PEM-formatted file
containing trusted X.509 certificates to be included in the default
system keyring. Any certificate used for module signing is implicitly
also trusted.
NOTE: If you previously provided keys for the system keyring in the
form of DER-encoded *.x509 files in the top-level build directory,
those are no longer used. You will need to set this option instead.
config SYSTEM_EXTRA_CERTIFICATE
bool "Reserve area for inserting a certificate without recompiling"
depends on SYSTEM_TRUSTED_KEYRING
help
If set, space for an extra certificate will be reserved in the kernel
image. This allows introducing a trusted certificate to the default
system keyring without recompiling the kernel.
config SYSTEM_EXTRA_CERTIFICATE_SIZE
int "Number of bytes to reserve for the extra certificate"
depends on SYSTEM_EXTRA_CERTIFICATE
default 4096
help
This is the number of bytes reserved in the kernel image for a
certificate to be inserted.
config SECONDARY_TRUSTED_KEYRING
bool "Provide a keyring to which extra trustable keys may be added"
depends on SYSTEM_TRUSTED_KEYRING
help
If set, provide a keyring to which extra keys may be added, provided
those keys are not blacklisted and are vouched for by a key built
into the kernel or already in the secondary trusted keyring.
config SYSTEM_BLACKLIST_KEYRING
bool "Provide system-wide ring of blacklisted keys"
depends on KEYS
help
Provide a system keyring to which blacklisted keys can be added.
Keys in the keyring are considered entirely untrusted. Keys in this
keyring are used by the module signature checking to reject loading
of modules signed with a blacklisted key.
config SYSTEM_BLACKLIST_HASH_LIST
string "Hashes to be preloaded into the system blacklist keyring"
depends on SYSTEM_BLACKLIST_KEYRING
help
If set, this option should be the filename of a list of hashes in the
form "<hash>", "<hash>", ... . This will be included into a C
wrapper to incorporate the list into the kernel. Each <hash> should
be a string of hex digits.
endmenu
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