Commit a4140162 authored by Mimi Zohar's avatar Mimi Zohar
Browse files

ima: limit the number of ToMToU integrity violations 



Each time a file in policy, that is already opened for read, is opened
for write, a Time-of-Measure-Time-of-Use (ToMToU) integrity violation
audit message is emitted and a violation record is added to the IMA
measurement list.  This occurs even if a ToMToU violation has already
been recorded.

Limit the number of ToMToU integrity violations per file open for read.

Note: The IMA_MAY_EMIT_TOMTOU atomic flag must be set from the reader
side based on policy.  This may result in a per file open for read
ToMToU violation.

Since IMA_MUST_MEASURE is only used for violations, rename the atomic
IMA_MUST_MEASURE flag to IMA_MAY_EMIT_TOMTOU.

Cc: stable@vger.kernel.org # applies cleanly up to linux-6.6
Tested-by: default avatarStefan Berger <stefanb@linux.ibm.com>
Reviewed-by: default avatarPetr Vorel <pvorel@suse.cz>
Tested-by: default avatarPetr Vorel <pvorel@suse.cz>
Reviewed-by: default avatarRoberto Sassu <roberto.sassu@huawei.com>
Signed-off-by: default avatarMimi Zohar <zohar@linux.ibm.com>
parent 5b3cd801

security/integrity/ima/ima.h

+1 −1
Original line number Diff line number Diff line
@@ -181,7 +181,7 @@ struct ima_kexec_hdr { 
#define IMA_UPDATE_XATTR	1

#define IMA_CHANGE_ATTR		2

#define IMA_DIGSIG		3

#define IMA_MUST_MEASURE	4

#define IMA_MAY_EMIT_TOMTOU	4

#define IMA_EMITTED_OPENWRITERS	5



/* IMA integrity metadata associated with an inode */

security/integrity/ima/ima_main.c

+4 −3
Original line number Diff line number Diff line
@@ -129,14 +129,15 @@ static void ima_rdwr_violation_check(struct file *file, 
		if (atomic_read(&inode->i_readcount) && IS_IMA(inode)) {

			if (!iint)

				iint = ima_iint_find(inode);



			/* IMA_MEASURE is set from reader side */

			if (iint && test_bit(IMA_MUST_MEASURE,

			if (iint && test_and_clear_bit(IMA_MAY_EMIT_TOMTOU,

						       &iint->atomic_flags))

				send_tomtou = true;

		}

	} else {

		if (must_measure)

			set_bit(IMA_MUST_MEASURE, &iint->atomic_flags);

			set_bit(IMA_MAY_EMIT_TOMTOU, &iint->atomic_flags);



		/* Limit number of open_writers violations */

		if (inode_is_open_for_write(inode) && must_measure) {