Patch "ima: detect changes to the backing overlay file" has been added to the 4.19-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    ima: detect changes to the backing overlay file

to the 4.19-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     ima-detect-changes-to-the-backing-overlay-file.patch
and it can be found in the queue-4.19 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 5e7f43bc3e5fe45a14cc65bb7571350d1bccf563
Author: Mimi Zohar <zohar@xxxxxxxxxxxxx>
Date:   Wed Oct 18 14:47:02 2023 -0400

    ima: detect changes to the backing overlay file
    
    [ Upstream commit b836c4d29f2744200b2af41e14bf50758dddc818 ]
    
    Commit 18b44bc5a672 ("ovl: Always reevaluate the file signature for
    IMA") forced signature re-evaulation on every file access.
    
    Instead of always re-evaluating the file's integrity, detect a change
    to the backing file, by comparing the cached file metadata with the
    backing file's metadata.  Verifying just the i_version has not changed
    is insufficient.  In addition save and compare the i_ino and s_dev
    as well.
    
    Reviewed-by: Amir Goldstein <amir73il@xxxxxxxxx>
    Tested-by: Eric Snowberg <eric.snowberg@xxxxxxxxxx>
    Tested-by: Raul E Rangel <rrangel@xxxxxxxxxxxx>
    Cc: stable@xxxxxxxxxxxxxxx
    Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c
index a02c5acfd403b..377a6f7cd3c76 100644
--- a/security/integrity/ima/ima_api.c
+++ b/security/integrity/ima/ima_api.c
@@ -201,6 +201,7 @@ int ima_collect_measurement(struct integrity_iint_cache *iint,
 {
 	const char *audit_cause = "failed";
 	struct inode *inode = file_inode(file);
+	struct inode *real_inode = d_real_inode(file_dentry(file));
 	const char *filename = file->f_path.dentry->d_name.name;
 	int result = 0;
 	int length;
@@ -243,6 +244,10 @@ int ima_collect_measurement(struct integrity_iint_cache *iint,
 	iint->ima_hash = tmpbuf;
 	memcpy(iint->ima_hash, &hash, length);
 	iint->version = i_version;
+	if (real_inode != inode) {
+		iint->real_ino = real_inode->i_ino;
+		iint->real_dev = real_inode->i_sb->s_dev;
+	}
 
 	/* Possibly temporary failure due to type of read (eg. O_DIRECT) */
 	if (!result)
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index c85aab3bd398b..d9a33d433b9fa 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -29,6 +29,7 @@
 #include <linux/ima.h>
 #include <linux/iversion.h>
 #include <linux/fs.h>
+#include <linux/iversion.h>
 
 #include "ima.h"
 
@@ -170,7 +171,7 @@ static int process_measurement(struct file *file, const struct cred *cred,
 			       u32 secid, char *buf, loff_t size, int mask,
 			       enum ima_hooks func)
 {
-	struct inode *inode = file_inode(file);
+	struct inode *backing_inode, *inode = file_inode(file);
 	struct integrity_iint_cache *iint = NULL;
 	struct ima_template_desc *template_desc;
 	char *pathbuf = NULL;
@@ -242,6 +243,19 @@ static int process_measurement(struct file *file, const struct cred *cred,
 		iint->measured_pcrs = 0;
 	}
 
+	/* Detect and re-evaluate changes made to the backing file. */
+	backing_inode = d_real_inode(file_dentry(file));
+	if (backing_inode != inode &&
+	    (action & IMA_DO_MASK) && (iint->flags & IMA_DONE_MASK)) {
+		if (!IS_I_VERSION(backing_inode) ||
+		    backing_inode->i_sb->s_dev != iint->real_dev ||
+		    backing_inode->i_ino != iint->real_ino ||
+		    !inode_eq_iversion(backing_inode, iint->version)) {
+			iint->flags &= ~IMA_DONE_MASK;
+			iint->measured_pcrs = 0;
+		}
+	}
+
 	/* Determine if already appraised/measured based on bitmask
 	 * (IMA_MEASURE, IMA_MEASURED, IMA_XXXX_APPRAISE, IMA_XXXX_APPRAISED,
 	 *  IMA_AUDIT, IMA_AUDITED)
diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h
index e60473b13a8d2..b0264ba45ddd1 100644
--- a/security/integrity/integrity.h
+++ b/security/integrity/integrity.h
@@ -122,6 +122,8 @@ struct integrity_iint_cache {
 	unsigned long flags;
 	unsigned long measured_pcrs;
 	unsigned long atomic_flags;
+	unsigned long real_ino;
+	dev_t real_dev;
 	enum integrity_status ima_file_status:4;
 	enum integrity_status ima_mmap_status:4;
 	enum integrity_status ima_bprm_status:4;