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: Petr Matousek <pmatouse@xxxxxxxxxx>
Signed-off-by: "Theodore Ts'o" <tytso@xxxxxxx>
Cc: stable@xxxxxxxxxx
---
fs/ext4/inode.c | 33 ++++++++++++++++++++-------------
1 file changed, 20 insertions(+), 13 deletions(-)
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index b5e182a..169fff3 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3937,19 +3937,26 @@ 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;
-
- inode->i_flags &= ~(S_SYNC|S_APPEND|S_IMMUTABLE|S_NOATIME|S_DIRSYNC);
- if (flags & EXT4_SYNC_FL)
- inode->i_flags |= S_SYNC;
- if (flags & EXT4_APPEND_FL)
- inode->i_flags |= S_APPEND;
- if (flags & EXT4_IMMUTABLE_FL)
- inode->i_flags |= S_IMMUTABLE;
- if (flags & EXT4_NOATIME_FL)
- inode->i_flags |= S_NOATIME;
- if (flags & EXT4_DIRSYNC_FL)
- inode->i_flags |= S_DIRSYNC;
+ unsigned int flags;
+ unsigned int old_fl, new_fl;
+
+ do {
+ flags = EXT4_I(inode)->i_flags;
+ old_fl = inode->i_flags;
+ new_fl = old_fl &
+ ~(S_SYNC|S_APPEND|S_IMMUTABLE|S_NOATIME|S_DIRSYNC);
+
+ if (flags & EXT4_SYNC_FL)
+ new_fl |= S_SYNC;
+ if (flags & EXT4_APPEND_FL)
+ new_fl |= S_APPEND;
+ if (flags & EXT4_IMMUTABLE_FL)
+ new_fl |= S_IMMUTABLE;
+ if (flags & EXT4_NOATIME_FL)
+ new_fl |= S_NOATIME;
+ if (flags & EXT4_DIRSYNC_FL)
+ new_fl |= S_DIRSYNC;
+ } while (cmpxchg(&inode->i_flags, old_fl, new_fl) != old_fl);
}
/* Propagate flags from i_flags to EXT4_I(inode)->i_flags */
--
1.9.0
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
