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Subject[patch] Fix block device inode list corruptions
From
Date
Hi,

I've been chasing a weird SELinux bug which shows up mostly when doing
installs of a dev-* rpm (ie. creating and overwriting lots of block
device inodes), but which I've also seen when doing mkinitrd.

It turned out not to be an SELinux problem at all, but a core VFS
S_ISBLK bug. It seems that SELinux simply widens the race window.

The code at fault is fs/fs-writeback.c:__mark_inode_dirty():

/*
* Only add valid (hashed) inodes to the superblock's
* dirty list. Add blockdev inodes as well.
*/
if (!S_ISBLK(inode->i_mode)) {
if (hlist_unhashed(&inode->i_hash))
goto out;
if (inode->i_state & (I_FREEING|I_CLEAR))
goto out;
}

The "I_FREEING|I_CLEAR" condition was added after the ISBLK/unhashed
tests were already in the source, but I can't see any reason why we'd
want the I_FREEING test not to apply to block devices. And indeed, this
results in all sorts of inode list corruptions. Simply moving the
I_FREEING|I_CLEAR test out of the protection of the S_ISBLK() condition
fixes things entirely.

The exiting 2.6 kernel will reliably fail on me in about 2 seconds once
"rpm -Uvh --force dev*.rpm" starts its actual installation of the new
inodes. With the patch below I can't reproduce it at all.

--Stephen





--- linux-2.6.1/fs/fs-writeback.c.=K0001=.orig
+++ linux-2.6.1/fs/fs-writeback.c
@@ -87,12 +87,11 @@ void __mark_inode_dirty(struct inode *in
* Only add valid (hashed) inodes to the superblock's
* dirty list. Add blockdev inodes as well.
*/
- if (!S_ISBLK(inode->i_mode)) {
+ if (!S_ISBLK(inode->i_mode))
if (hlist_unhashed(&inode->i_hash))
goto out;
- if (inode->i_state & (I_FREEING|I_CLEAR))
- goto out;
- }
+ if (inode->i_state & (I_FREEING|I_CLEAR))
+ goto out;

/*
* If the inode was already on s_dirty or s_io, don't
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