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
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index abc9ca7..be5fd38 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -196,6 +196,21 @@
#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