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authorTheodore Ts'o <tytso@mit.edu>2014-03-24 14:43:12 -0400
committerTheodore Ts'o <tytso@mit.edu>2014-03-24 14:43:12 -0400
commit5f16f3225b06242a9ee876f07c1c9b6ed36a22b6 (patch)
treecebecf399c2d9ef5b0a24902638cb37d2e9e092b /fs/inode.c
parented3654eb981fd44694b4d2a636e13f998bc10e7f (diff)
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: John Sullivan <jsrhbz@kanargh.force9.co.uk> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu> Cc: stable@kernel.org
Diffstat (limited to 'fs/inode.c')
-rw-r--r--fs/inode.c31
1 files changed, 31 insertions, 0 deletions
diff --git a/fs/inode.c b/fs/inode.c
index 4bcdad3c936..26f95ceb625 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -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);