From 5b3cd801155f0b34b0b95942a5b057c9b8cad33e Mon Sep 17 00:00:00 2001 From: Mimi Zohar Date: Mon, 27 Jan 2025 10:24:13 -0500 Subject: [PATCH 1/2] ima: limit the number of open-writers integrity violations Each time a file in policy, that is already opened for write, is opened for read, an open-writers integrity violation audit message is emitted and a violation record is added to the IMA measurement list. This occurs even if an open-writers violation has already been recorded. Limit the number of open-writers integrity violations for an existing file open for write to one. After the existing file open for write closes (__fput), subsequent open-writers integrity violations may be emitted. Cc: stable@vger.kernel.org # applies cleanly up to linux-6.6 Tested-by: Stefan Berger Reviewed-by: Petr Vorel Tested-by: Petr Vorel Reviewed-by: Roberto Sassu Signed-off-by: Mimi Zohar --- security/integrity/ima/ima.h | 1 + security/integrity/ima/ima_main.c | 11 +++++++++-- 2 files changed, 10 insertions(+), 2 deletions(-) diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h index a4f284bd846c..3423b3088de5 100644 --- a/security/integrity/ima/ima.h +++ b/security/integrity/ima/ima.h @@ -182,6 +182,7 @@ struct ima_kexec_hdr { #define IMA_CHANGE_ATTR 2 #define IMA_DIGSIG 3 #define IMA_MUST_MEASURE 4 +#define IMA_EMITTED_OPENWRITERS 5 /* IMA integrity metadata associated with an inode */ struct ima_iint_cache { diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c index 28b8b0db6f9b..95118c1887cb 100644 --- a/security/integrity/ima/ima_main.c +++ b/security/integrity/ima/ima_main.c @@ -137,8 +137,13 @@ static void ima_rdwr_violation_check(struct file *file, } else { if (must_measure) set_bit(IMA_MUST_MEASURE, &iint->atomic_flags); - if (inode_is_open_for_write(inode) && must_measure) - send_writers = true; + + /* 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) @@ -167,6 +172,8 @@ static void ima_check_last_writer(struct ima_iint_cache *iint, if (atomic_read(&inode->i_writecount) == 1) { struct kstat stat; + clear_bit(IMA_EMITTED_OPENWRITERS, &iint->atomic_flags); + update = test_and_clear_bit(IMA_UPDATE_XATTR, &iint->atomic_flags); if ((iint->flags & IMA_NEW_FILE) || From a414016218ca97140171aa3bb926b02e1f68c2cc Mon Sep 17 00:00:00 2001 From: Mimi Zohar Date: Mon, 27 Jan 2025 10:45:48 -0500 Subject: [PATCH 2/2] 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 Reviewed-by: Petr Vorel Tested-by: Petr Vorel Reviewed-by: Roberto Sassu Signed-off-by: Mimi Zohar --- security/integrity/ima/ima.h | 2 +- security/integrity/ima/ima_main.c | 7 ++++--- 2 files changed, 5 insertions(+), 4 deletions(-) diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h index 3423b3088de5..e0489c6f7f59 100644 --- 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 95118c1887cb..f3e7ac513db3 100644 --- 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) {