ima: detect changes to the backing overlay file

commit b836c4d29f2744200b2af41e14bf50758dddc818 upstream.

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@gmail.com>
Tested-by: Eric Snowberg <eric.snowberg@oracle.com>
Tested-by: Raul E Rangel <rrangel@chromium.org>
Cc: stable@vger.kernel.org
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 3fa2416..c71d185 100644 (file)
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -1489,7 +1489,7 @@ int ovl_fill_super(struct super_block *sb, struct fs_context *fc)
                ovl_trusted_xattr_handlers;
        sb->s_fs_info = ofs;
        sb->s_flags |= SB_POSIXACL;
-       sb->s_iflags |= SB_I_SKIP_SYNC | SB_I_IMA_UNVERIFIABLE_SIGNATURE;
+       sb->s_iflags |= SB_I_SKIP_SYNC;
 
        err = -ENOMEM;
        root_dentry = ovl_get_root(sb, ctx->upper.dentry, oe);

diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c
index 452e80b..597ea0c 100644 (file)
--- a/security/integrity/ima/ima_api.c
+++ b/security/integrity/ima/ima_api.c
@@ -243,6 +243,7 @@ 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;
        struct ima_max_digest_data hash;
        struct kstat stat;
@@ -302,6 +303,10 @@ 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 365db0e..cc1217a 100644 (file)
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -25,6 +25,7 @@
 #include <linux/xattr.h>
 #include <linux/ima.h>
 #include <linux/fs.h>
+#include <linux/iversion.h>
 
 #include "ima.h"
 
@@ -207,7 +208,7 @@ 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 = NULL;
        char *pathbuf = NULL;
@@ -284,6 +285,19 @@ 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 d7553c9..9561db7 100644 (file)
--- a/security/integrity/integrity.h
+++ b/security/integrity/integrity.h
@@ -164,6 +164,8 @@ 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;