On Fri, May 04, 2012 at 11:37:49PM +0800, Tao Ma wrote: > From: Tao Ma <[email protected]> > > In commit 353eb83c we removes i_state_flags with 64-bit longs, > But in case we call EXT4_IOC_SETFLAGS, we fail to save the > high 32-bit state flags and only stores the low 32-bit back > to ei->i_flags. So the state flags are missing now in 64-bit > long architecture.
The problem with this approach is that we are still editing i_flags and then replacing it with the new value. So we're vulnerable to races where some other process is modifies the i_state_flags between when we sample it using ext4_save_state_flags() and when we restore them. This is a better way to fix the problem, and what I plan to commit into the ext4 tree: commit 79906964a187c405db72a3abc60eb9b50d804fbc Author: Theodore Ts'o <[email protected]> Date: Thu May 31 23:46:01 2012 -0400 ext4: don't trash state flags in EXT4_IOC_SETFLAGS In commit 353eb83c we removed i_state_flags with 64-bit longs, But when handling the EXT4_IOC_SETFLAGS ioctl, we replace i_flags directly, which trashes the state flags which are stored in the high 32-bits of i_flags on 64-bit platforms. So use the the ext4_{set,clear}_inode_flags() functions which use atomic bit manipulation functions instead. Reported-by: Tao Ma <[email protected]> Signed-off-by: "Theodore Ts'o" <[email protected]> Cc: [email protected] diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c index feba55a..8ad112a 100644 --- a/fs/ext4/ioctl.c +++ b/fs/ext4/ioctl.c @@ -38,7 +38,7 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) handle_t *handle = NULL; int err, migrate = 0; struct ext4_iloc iloc; - unsigned int oldflags; + unsigned int oldflags, mask, i; unsigned int jflag; if (!inode_owner_or_capable(inode)) @@ -115,8 +115,14 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) if (err) goto flags_err; - flags = flags & EXT4_FL_USER_MODIFIABLE; - flags |= oldflags & ~EXT4_FL_USER_MODIFIABLE; + for (i = 0, mask = 1; i < 32; i++, mask <<= 1) { + if (!(mask & EXT4_FL_USER_MODIFIABLE)) + continue; + if (mask & flags) + ext4_set_inode_flag(inode, i); + else + ext4_clear_inode_flag(inode, i); + } ei->i_flags = flags; ext4_set_inode_flags(inode); -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
