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Commit 00a1a053 authored by Theodore Ts'o's avatar Theodore Ts'o Committed by Linus Torvalds
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ext4: atomically set inode->i_flags in ext4_set_inode_flags() 



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: default avatarJohn Sullivan <jsrhbz@kanargh.force9.co.uk>
Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
Cc: stable@kernel.org
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 981e893e

fs/ext4/inode.c

+9 −6
Original line number Diff line number Diff line
@@ -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"
@@ -3921,18 +3922,20 @@ int ext4_get_inode_loc(struct inode *inode, struct ext4_iloc *iloc) 
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 */

include/linux/bitops.h

+15 −0
Original line number Diff line number Diff line
@@ -196,6 +196,21 @@ static inline unsigned long __ffs64(u64 word) 


#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