syzbot reports data-race in fat32_ent_get/fat32_ent_put. CPU0(Task A) CPU1(Task B) ==== ==== vfs_write new_sync_write generic_file_write_iter fat_write_begin block_write_begin vfs_statfs fat_get_block statfs_by_dentry fat_add_cluster fat_statfs fat_ent_write fat_count_free_clusters fat32_ent_put fat32_ent_get Task A's write operation on CPU0 and Task B's read operation on CPU1 occur simultaneously, generating an race condition. Add READ/WRITE_ONCE to solve the race condition that occurs when accessing FAT32 entry. Reported-by: syzbot+d3c29ed63db6ddf8406e@xxxxxxxxxxxxxxxxxxxxxxxxx Closes: https://syzkaller.appspot.com/bug?extid=d3c29ed63db6ddf8406e Signed-off-by: Edward Adam Davis <eadavis@xxxxxx> --- V1 -> V2: using READ/WRITE_ONCE to fix fs/fat/fatent.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/fs/fat/fatent.c b/fs/fat/fatent.c index 1db348f8f887..a9eecd090d91 100644 --- a/fs/fat/fatent.c +++ b/fs/fat/fatent.c @@ -146,8 +146,8 @@ static int fat16_ent_get(struct fat_entry *fatent) static int fat32_ent_get(struct fat_entry *fatent) { - int next = le32_to_cpu(*fatent->u.ent32_p) & 0x0fffffff; - WARN_ON((unsigned long)fatent->u.ent32_p & (4 - 1)); + int next = le32_to_cpu(READ_ONCE(*fatent->u.ent32_p)) & 0x0fffffff; + WARN_ON((unsigned long)READ_ONCE(fatent->u.ent32_p) & (4 - 1)); if (next >= BAD_FAT32) next = FAT_ENT_EOF; return next; @@ -187,8 +187,8 @@ static void fat16_ent_put(struct fat_entry *fatent, int new) static void fat32_ent_put(struct fat_entry *fatent, int new) { WARN_ON(new & 0xf0000000); - new |= le32_to_cpu(*fatent->u.ent32_p) & ~0x0fffffff; - *fatent->u.ent32_p = cpu_to_le32(new); + new |= le32_to_cpu(READ_ONCE(*fatent->u.ent32_p)) & ~0x0fffffff; + WRITE_ONCE(*fatent->u.ent32_p, cpu_to_le32(new)); mark_buffer_dirty_inode(fatent->bhs[0], fatent->fat_inode); } -- 2.43.0
