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: Stefan Berger <stefanb@linux.ibm.com>
Reviewed-by: Petr Vorel <pvorel@suse.cz>
Tested-by: Petr Vorel <pvorel@suse.cz>
Reviewed-by: Roberto Sassu <roberto.sassu@huawei.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 3423b3088de5080c5b49935037021bd5da3d1ccb..e0489c6f7f596196e8848731c9d5b801ae20f224 100644 (file)
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -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 */

diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 95118c1887cb69c2c4650d086df24088b25cfa3e..f3e7ac513db3f5e4791670a071eee55b9fdf8ace 100644 (file)
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -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,
-                                               &iint->atomic_flags))
+                       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) {