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Commit 5f16f322 authored by Theodore Ts'o's avatar Theodore Ts'o
Browse files

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
parent ed3654eb

fs/ext4/inode.c

+8 −6
Original line number Diff line number Diff line
@@ -3938,18 +3938,20 @@ 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;

	inode_set_flags(inode, new_fl,

			S_SYNC|S_APPEND|S_IMMUTABLE|S_NOATIME|S_DIRSYNC);

}



/* Propagate flags from i_flags to EXT4_I(inode)->i_flags */

fs/inode.c

+31 −0
Original line number Diff line number Diff line
@@ -1899,3 +1899,34 @@ void inode_dio_done(struct inode *inode) 
		wake_up_bit(&inode->i_state, __I_DIO_WAKEUP);

}

EXPORT_SYMBOL(inode_dio_done);



/*

 * inode_set_flags - atomically set some inode flags

 *

 * Note: the caller should be holding i_mutex, or else be sure that

 * they have exclusive access to the inode structure (i.e., while the

 * inode is being instantiated).  The reason for the cmpxchg() loop

 * --- which wouldn't be necessary if all code paths which modify

 * i_flags actually followed this rule, is that there is at least one

 * code path which doesn't today --- for example,

 * __generic_file_aio_write() calls file_remove_suid() without holding

 * i_mutex --- so we use cmpxchg() out of an abundance of caution.

 *

 * In the long run, i_mutex is overkill, and we should probably look

 * at using the i_lock spinlock to protect i_flags, and then make sure

 * it is so documented in include/linux/fs.h and that all code follows

 * the locking convention!!

 */

void inode_set_flags(struct inode *inode, unsigned int flags,

		     unsigned int mask)

{

	unsigned int old_flags, new_flags;



	WARN_ON_ONCE(flags & ~mask);

	do {

		old_flags = ACCESS_ONCE(inode->i_flags);

		new_flags = (old_flags & ~mask) | flags;

	} while (unlikely(cmpxchg(&inode->i_flags, old_flags,

				  new_flags) != old_flags));

}

EXPORT_SYMBOL(inode_set_flags);

include/linux/fs.h

+3 −0
Original line number Diff line number Diff line
@@ -2556,6 +2556,9 @@ static inline ssize_t blockdev_direct_IO(int rw, struct kiocb *iocb, 
void inode_dio_wait(struct inode *inode);

void inode_dio_done(struct inode *inode);



extern void inode_set_flags(struct inode *inode, unsigned int flags,

			    unsigned int mask);



extern const struct file_operations generic_ro_fops;



#define special_file(m) (S_ISCHR(m)||S_ISBLK(m)||S_ISFIFO(m)||S_ISSOCK(m))