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.
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| @@ -196,6 +196,21 @@ static inline unsigned long __ffs64(u64 word) · 195 unmodified lines | ||
| 196 | 196 | |
| 197 | 197 | #ifdef __KERNEL__ |
| 198 | 198 | |
| 199 | +#ifndef set_mask_bits | |
| 200 | +#define set_mask_bits(ptr, _mask, _bits) \ | |
| 201 | +({ \ | |
| 202 | + const typeof(*ptr) mask = (_mask), bits = (_bits); \ | |
| 203 | + typeof(*ptr) old, new; \ | |
| 204 | + \ | |
| 205 | + do { \ | |
| 206 | + old = ACCESS_ONCE(*ptr); \ | |
| 207 | + new = (old & ~mask) | bits; \ | |
| 208 | + } while (cmpxchg(ptr, old, new) != old); \ | |
| 209 | + \ | |
| 210 | + new; \ | |
| 211 | +}) | |
| 212 | +#endif | |
| 213 | + | |
| 199 | 214 | #ifndef find_last_bit |
| 200 | 215 | /** |
| 201 | 216 | * find_last_bit - find the last set bit in a memory region |