ima: limit the number of ToMToU integrity violations

[ Upstream commit a414016218ca97140171aa3bb926b02e1f68c2cc ]

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>
[ adapted IMA flag definitions location from ima.h to integrity.h ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 068edb0d79f7360233c63e76e33906943febb21d..3b734a4dfcbe4e54ecb759ecb23c8e84c739c1cb 100644 (file)
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -128,16 +128,22 @@ static void ima_rdwr_violation_check(struct file *file,
                if (atomic_read(&inode->i_readcount) && IS_IMA(inode)) {
                        if (!iint)
                                iint = integrity_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);
-               if (inode_is_open_for_write(inode) && must_measure)
-                       send_writers = true;
+                       set_bit(IMA_MAY_EMIT_TOMTOU, &iint->atomic_flags);
+
+               /* Limit number of open_writers violations */
+               if (inode_is_open_for_write(inode) && must_measure) {
+                       if (!test_and_set_bit(IMA_EMITTED_OPENWRITERS,
+                                             &iint->atomic_flags))
+                               send_writers = true;
+               }
        }
 
        if (!send_tomtou && !send_writers)

diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h
index ad20ff7f5dfaa44231e969dff777d9d4a3b0a35b..a007edae938aeb1748b4d4999f1e76a0e00bd0c4 100644 (file)
--- a/security/integrity/integrity.h
+++ b/security/integrity/integrity.h
@@ -74,7 +74,8 @@
 #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
 
 enum evm_ima_xattr_type {
        IMA_XATTR_DIGEST = 0x01,