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author | Dmitry Kasatkin <dmitry.kasatkin@gmail.com> | 2017-12-05 21:06:34 +0200 |
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committer | Mimi Zohar <zohar@linux.vnet.ibm.com> | 2017-12-11 17:20:47 -0500 |
commit | 0d73a55208e94fc9fb6deaeea61438cd3280d4c0 (patch) | |
tree | 7f32904e7fadf1c5721aca841f12b43287c5181b /security/integrity/ima/ima_appraise.c | |
parent | 50b977481fce90aa5fbda55e330b9d722733e358 (diff) | |
download | linux-0d73a55208e94fc9fb6deaeea61438cd3280d4c0.tar.bz2 |
ima: re-introduce own integrity cache lock
Before IMA appraisal was introduced, IMA was using own integrity cache
lock along with i_mutex. process_measurement and ima_file_free took
the iint->mutex first and then the i_mutex, while setxattr, chmod and
chown took the locks in reverse order. To resolve the potential deadlock,
i_mutex was moved to protect entire IMA functionality and the redundant
iint->mutex was eliminated.
Solution was based on the assumption that filesystem code does not take
i_mutex further. But when file is opened with O_DIRECT flag, direct-io
implementation takes i_mutex and produces deadlock. Furthermore, certain
other filesystem operations, such as llseek, also take i_mutex.
More recently some filesystems have replaced their filesystem specific
lock with the global i_rwsem to read a file. As a result, when IMA
attempts to calculate the file hash, reading the file attempts to take
the i_rwsem again.
To resolve O_DIRECT related deadlock problem, this patch re-introduces
iint->mutex. But to eliminate the original chmod() related deadlock
problem, this patch eliminates the requirement for chmod hooks to take
the iint->mutex by introducing additional atomic iint->attr_flags to
indicate calling of the hooks. The allowed locking order is to take
the iint->mutex first and then the i_rwsem.
Original flags were cleared in chmod(), setxattr() or removwxattr()
hooks and tested when file was closed or opened again. New atomic flags
are set or cleared in those hooks and tested to clear iint->flags on
close or on open.
Atomic flags are following:
* IMA_CHANGE_ATTR - indicates that chATTR() was called (chmod, chown,
chgrp) and file attributes have changed. On file open, it causes IMA
to clear iint->flags to re-evaluate policy and perform IMA functions
again.
* IMA_CHANGE_XATTR - indicates that setxattr or removexattr was called
and extended attributes have changed. On file open, it causes IMA to
clear iint->flags IMA_DONE_MASK to re-appraise.
* IMA_UPDATE_XATTR - indicates that security.ima needs to be updated.
It is cleared if file policy changes and no update is needed.
* IMA_DIGSIG - indicates that file security.ima has signature and file
security.ima must not update to file has on file close.
* IMA_MUST_MEASURE - indicates the file is in the measurement policy.
Fixes: Commit 6552321831dc ("xfs: remove i_iolock and use i_rwsem in
the VFS inode instead")
Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@huawei.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Diffstat (limited to 'security/integrity/ima/ima_appraise.c')
-rw-r--r-- | security/integrity/ima/ima_appraise.c | 27 |
1 files changed, 14 insertions, 13 deletions
diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c index 084c19e45668..ea1245606a14 100644 --- a/security/integrity/ima/ima_appraise.c +++ b/security/integrity/ima/ima_appraise.c @@ -251,6 +251,7 @@ int ima_appraise_measurement(enum ima_hooks func, status = INTEGRITY_FAIL; break; } + clear_bit(IMA_DIGSIG, &iint->atomic_flags); if (xattr_len - sizeof(xattr_value->type) - hash_start >= iint->ima_hash->length) /* xattr length may be longer. md5 hash in previous @@ -269,7 +270,7 @@ int ima_appraise_measurement(enum ima_hooks func, status = INTEGRITY_PASS; break; case EVM_IMA_XATTR_DIGSIG: - iint->flags |= IMA_DIGSIG; + set_bit(IMA_DIGSIG, &iint->atomic_flags); rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA, (const char *)xattr_value, rc, iint->ima_hash->digest, @@ -320,7 +321,7 @@ void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file) int rc = 0; /* do not collect and update hash for digital signatures */ - if (iint->flags & IMA_DIGSIG) + if (test_bit(IMA_DIGSIG, &iint->atomic_flags)) return; if (iint->ima_file_status != INTEGRITY_PASS) @@ -330,7 +331,9 @@ void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file) if (rc < 0) return; + inode_lock(file_inode(file)); ima_fix_xattr(dentry, iint); + inode_unlock(file_inode(file)); } /** @@ -353,16 +356,14 @@ void ima_inode_post_setattr(struct dentry *dentry) return; must_appraise = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR); + if (!must_appraise) + __vfs_removexattr(dentry, XATTR_NAME_IMA); iint = integrity_iint_find(inode); if (iint) { - iint->flags &= ~(IMA_APPRAISE | IMA_APPRAISED | - IMA_APPRAISE_SUBMASK | IMA_APPRAISED_SUBMASK | - IMA_ACTION_RULE_FLAGS); - if (must_appraise) - iint->flags |= IMA_APPRAISE; + set_bit(IMA_CHANGE_ATTR, &iint->atomic_flags); + if (!must_appraise) + clear_bit(IMA_UPDATE_XATTR, &iint->atomic_flags); } - if (!must_appraise) - __vfs_removexattr(dentry, XATTR_NAME_IMA); } /* @@ -391,12 +392,12 @@ static void ima_reset_appraise_flags(struct inode *inode, int digsig) iint = integrity_iint_find(inode); if (!iint) return; - - iint->flags &= ~IMA_DONE_MASK; iint->measured_pcrs = 0; + set_bit(IMA_CHANGE_XATTR, &iint->atomic_flags); if (digsig) - iint->flags |= IMA_DIGSIG; - return; + set_bit(IMA_DIGSIG, &iint->atomic_flags); + else + clear_bit(IMA_DIGSIG, &iint->atomic_flags); } int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name, |