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.
Unified · Split
| @@ -38,6 +38,7 @@ · 37 unmodified lines | ||
| 38 | 38 | #include <linux/slab.h> |
| 39 | 39 | #include <linux/ratelimit.h> |
| 40 | 40 | #include <linux/aio.h> |
| 41 | +#include <linux/bitops.h> | |
| 41 | 42 | |
| 42 | 43 | #include "ext4_jbd2.h" |
| 43 | 44 | #include "xattr.h" |
| @@ -3921,18 +3922,20 @@ int ext4_get_inode_loc(struct inode *inode, struct ext4_iloc *iloc) · 3877 unmodified lines | ||
| 3921 | 3922 | void ext4_set_inode_flags(struct inode *inode) |
| 3922 | 3923 | { |
| 3923 | 3924 | unsigned int flags = EXT4_I(inode)->i_flags; |
| 3925 | + unsigned int new_fl = 0; | |
| 3924 | 3926 | |
| 3925 | − inode->i_flags &= ~(S_SYNC|S_APPEND|S_IMMUTABLE|S_NOATIME|S_DIRSYNC); | |
| 3926 | 3927 | if (flags & EXT4_SYNC_FL) |
| 3927 | − inode->i_flags |= S_SYNC; | |
| 3928 | + new_fl |= S_SYNC; | |
| 3928 | 3929 | if (flags & EXT4_APPEND_FL) |
| 3929 | − inode->i_flags |= S_APPEND; | |
| 3930 | + new_fl |= S_APPEND; | |
| 3930 | 3931 | if (flags & EXT4_IMMUTABLE_FL) |
| 3931 | − inode->i_flags |= S_IMMUTABLE; | |
| 3932 | + new_fl |= S_IMMUTABLE; | |
| 3932 | 3933 | if (flags & EXT4_NOATIME_FL) |
| 3933 | − inode->i_flags |= S_NOATIME; | |
| 3934 | + new_fl |= S_NOATIME; | |
| 3934 | 3935 | if (flags & EXT4_DIRSYNC_FL) |
| 3935 | − inode->i_flags |= S_DIRSYNC; | |
| 3936 | + new_fl |= S_DIRSYNC; | |
| 3937 | + set_mask_bits(&inode->i_flags, | |
| 3938 | + S_SYNC|S_APPEND|S_IMMUTABLE|S_NOATIME|S_DIRSYNC, new_fl); | |
| 3936 | 3939 | } |
| 3937 | 3940 | |
| 3938 | 3941 | /* Propagate flags from i_flags to EXT4_I(inode)->i_flags */ |
| @@ -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 |