On Mon, Mar 31, 2014 at 03:15:44PM -0700, [email protected] wrote:
>
> This is a note to let you know that I've just added the patch titled
>
> ext4: atomically set inode->i_flags in ext4_set_inode_flags()
>
> to the 3.10-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:
> ext4-atomically-set-inode-i_flags-in-ext4_set_inode_flags.patch
> and it can be found in the queue-3.10 subdirectory.
I was going to make a one or two minor changes based on akpm's
changes, and this change hasn't been merged upstream yet. The plan
was for this to go upstream in a few more days, after we finish off
some last minute testing, and and fixing a bug in an existing patch in
the ext4 tree that was discovered last week, so if you want to wait a
week, this patch should be upstream by then (and hopefully sooner).
OTOH, this is a security fix, and the bug has been reported and
outstanding for a while, so if you want to push this sooner, that's
fine.
It should also be noted that a similar bug exists for btrfs and
several other file systems (although btrfs is probably the most
important mainstream fs that should get fixed sooner rather than
later).
Cheers,
- Ted
> If you, or anyone else, feels it should not be added to the stable tree,
> please let <[email protected]> know about it.
>
>
> From 00a1a053ebe5febcfc2ec498bd894f035ad2aa06 Mon Sep 17 00:00:00 2001
> From: Theodore Ts'o <[email protected]>
> Date: Sun, 30 Mar 2014 10:20:01 -0400
> Subject: ext4: atomically set inode->i_flags in ext4_set_inode_flags()
>
> From: Theodore Ts'o <[email protected]>
>
> commit 00a1a053ebe5febcfc2ec498bd894f035ad2aa06 upstream.
>
> Use cmpxchg() to atomically set i_flags instead of clearing out the
> S_IMMUTABLE, S_APPEND, etc. flags and then setting them from the
> EXT4_IMMUTABLE_FL, EXT4_APPEND_FL flags, since this opens up a race
> where an immutable file has the immutable flag cleared for a brief
> window of time.
>
> Reported-by: John Sullivan <[email protected]>
> Signed-off-by: "Theodore Ts'o" <[email protected]>
> Signed-off-by: Linus Torvalds <[email protected]>
> Signed-off-by: Greg Kroah-Hartman <[email protected]>
>
> ---
> fs/ext4/inode.c | 15 +++++++++------
> include/linux/bitops.h | 15 +++++++++++++++
> 2 files changed, 24 insertions(+), 6 deletions(-)
>
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -38,6 +38,7 @@
> #include <linux/slab.h>
> #include <linux/ratelimit.h>
> #include <linux/aio.h>
> +#include <linux/bitops.h>
>
> #include "ext4_jbd2.h"
> #include "xattr.h"
> @@ -4044,18 +4045,20 @@ int ext4_get_inode_loc(struct inode *ino
> void ext4_set_inode_flags(struct inode *inode)
> {
> unsigned int flags = EXT4_I(inode)->i_flags;
> + unsigned int new_fl = 0;
>
> - inode->i_flags &= ~(S_SYNC|S_APPEND|S_IMMUTABLE|S_NOATIME|S_DIRSYNC);
> if (flags & EXT4_SYNC_FL)
> - inode->i_flags |= S_SYNC;
> + new_fl |= S_SYNC;
> if (flags & EXT4_APPEND_FL)
> - inode->i_flags |= S_APPEND;
> + new_fl |= S_APPEND;
> if (flags & EXT4_IMMUTABLE_FL)
> - inode->i_flags |= S_IMMUTABLE;
> + new_fl |= S_IMMUTABLE;
> if (flags & EXT4_NOATIME_FL)
> - inode->i_flags |= S_NOATIME;
> + new_fl |= S_NOATIME;
> if (flags & EXT4_DIRSYNC_FL)
> - inode->i_flags |= S_DIRSYNC;
> + new_fl |= S_DIRSYNC;
> + set_mask_bits(&inode->i_flags,
> + S_SYNC|S_APPEND|S_IMMUTABLE|S_NOATIME|S_DIRSYNC, new_fl);
> }
>
> /* Propagate flags from i_flags to EXT4_I(inode)->i_flags */
> --- a/include/linux/bitops.h
> +++ b/include/linux/bitops.h
> @@ -185,6 +185,21 @@ static inline unsigned long __ffs64(u64
>
> #ifdef __KERNEL__
>
> +#ifndef set_mask_bits
> +#define set_mask_bits(ptr, _mask, _bits) \
> +({ \
> + const typeof(*ptr) mask = (_mask), bits = (_bits); \
> + typeof(*ptr) old, new; \
> + \
> + do { \
> + old = ACCESS_ONCE(*ptr); \
> + new = (old & ~mask) | bits; \
> + } while (cmpxchg(ptr, old, new) != old); \
> + \
> + new; \
> +})
> +#endif
> +
> #ifndef find_last_bit
> /**
> * find_last_bit - find the last set bit in a memory region
>
>
> Patches currently in stable-queue which might be from [email protected] are
>
> queue-3.10/ext4-atomically-set-inode-i_flags-in-ext4_set_inode_flags.patch
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