From b9593d309d17c57e9ddc3934d641902533896ca9 Mon Sep 17 00:00:00 2001 From: Eric Paris Date: Mon, 25 Oct 2010 14:41:52 -0400 Subject: [PATCH] IMA: use i_writecount rather than a private counter IMA tracks the number of struct files which are holding a given inode readonly and the number which are holding the inode write or r/w. It needs this information so when a new reader or writer comes in it can tell if this new file will be able to invalidate results it already made about existing files. aka if a task is holding a struct file open RO, IMA measured the file and recorded those measurements and then a task opens the file RW IMA needs to note in the logs that the old measurement may not be correct. It's called a "Time of Measure Time of Use" (ToMToU) issue. The same is true is a RO file is opened to an inode which has an open writer. We cannot, with any validity, measure the file in question since it could be changing. This patch attempts to use the i_writecount field to track writers. The i_writecount field actually embeds more information in it's value than IMA needs but it should work for our purposes and allow us to shrink the struct inode even more. Signed-off-by: Eric Paris Acked-by: Mimi Zohar Signed-off-by: Linus Torvalds --- security/integrity/ima/ima.h | 1 - security/integrity/ima/ima_iint.c | 6 ------ security/integrity/ima/ima_main.c | 16 ++++++---------- 3 files changed, 6 insertions(+), 17 deletions(-) diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h index 80aca3d2cb71..b546b90f5fa8 100644 --- a/security/integrity/ima/ima.h +++ b/security/integrity/ima/ima.h @@ -108,7 +108,6 @@ struct ima_iint_cache { struct mutex mutex; /* protects: version, flags, digest */ /* protected by inode->i_lock */ unsigned int readcount; /* measured files readcount */ - unsigned int writecount;/* measured files writecount */ struct kref refcount; /* ima_iint_cache reference count */ }; diff --git a/security/integrity/ima/ima_iint.c b/security/integrity/ima/ima_iint.c index db71a13f27fe..e68891f8d55a 100644 --- a/security/integrity/ima/ima_iint.c +++ b/security/integrity/ima/ima_iint.c @@ -129,11 +129,6 @@ void iint_free(struct kref *kref) iint->readcount); iint->readcount = 0; } - if (iint->writecount != 0) { - printk(KERN_INFO "%s: writecount: %u\n", __func__, - iint->writecount); - iint->writecount = 0; - } kref_init(&iint->refcount); kmem_cache_free(iint_cache, iint); } @@ -166,7 +161,6 @@ static void init_once(void *foo) iint->flags = 0UL; mutex_init(&iint->mutex); iint->readcount = 0; - iint->writecount = 0; kref_init(&iint->refcount); } diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c index 2f9b5d50424e..24660bf3f82a 100644 --- a/security/integrity/ima/ima_main.c +++ b/security/integrity/ima/ima_main.c @@ -94,8 +94,6 @@ static void ima_inc_counts(struct ima_iint_cache *iint, fmode_t mode) if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ) iint->readcount++; - if (mode & FMODE_WRITE) - iint->writecount++; } /* @@ -173,18 +171,16 @@ static void ima_dec_counts(struct ima_iint_cache *iint, struct inode *inode, iint->readcount--; } if (mode & FMODE_WRITE) { - if (unlikely(iint->writecount == 0)) + if (atomic_read(&inode->i_writecount) <= 0) dump = true; - iint->writecount--; - if (iint->writecount == 0) { - if (iint->version != inode->i_version) - iint->flags &= ~IMA_MEASURED; - } + if (atomic_read(&inode->i_writecount) == 1 && + iint->version != inode->i_version) + iint->flags &= ~IMA_MEASURED; } if (dump && !ima_limit_imbalance(file)) { - printk(KERN_INFO "%s: open/free imbalance (r:%u w:%u)\n", - __func__, iint->readcount, iint->writecount); + printk(KERN_INFO "%s: open/free imbalance (r:%u)\n", + __func__, iint->readcount); dump_stack(); } } -- 2.39.5