From 5b808a2300a5ac45f4798ebfac8b367e98a4b692 Mon Sep 17 00:00:00 2001 From: Krzysztof Kozlowski Date: Wed, 16 Oct 2013 13:47:06 -0700 Subject: [PATCH] swap: fix set_blocksize race during swapon/swapoff Fix race between swapoff and swapon. Swapoff used old_block_size from swap_info outside of swapon_mutex so it could be overwritten by concurrent swapon. The race has visible effect only if more than one swap block device exists with different block sizes (e.g. /dev/sda1 with block size 4096 and /dev/sdb1 with 512). In such case it leads to setting the blocksize of swapped off device with wrong blocksize. The bug can be triggered with multiple concurrent swapoff and swapon: 0. Swap for some device is on. 1. swapoff: First the swapoff is called on this device and "struct swap_info_struct *p" is assigned. This is done under swap_lock however this lock is released for the call try_to_unuse(). 2. swapon: After the assignment above (and before acquiring swapon_mutex & swap_lock by swapoff) the swapon is called on the same device. The p->old_block_size is assigned to the value of block_size the device. This block size should be the same as previous but sometimes it is not. The swapon ends successfully. 3. swapoff: Swapoff resumes, grabs the locks and mutex and continues to disable this swap device. Now it sets the block size to value taken from swap_info which was overwritten by swapon in 2. Signed-off-by: Krzysztof Kozlowski Reported-by: Weijie Yang Cc: Bob Liu Cc: Konrad Rzeszutek Wilk Cc: Shaohua Li Cc: Minchan Kim Acked-by: Hugh Dickins Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/swapfile.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/mm/swapfile.c b/mm/swapfile.c index 3963fc24fcc1..de7c904e52e5 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -1824,6 +1824,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) struct filename *pathname; int i, type, prev; int err; + unsigned int old_block_size; if (!capable(CAP_SYS_ADMIN)) return -EPERM; @@ -1914,6 +1915,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) } swap_file = p->swap_file; + old_block_size = p->old_block_size; p->swap_file = NULL; p->max = 0; swap_map = p->swap_map; @@ -1938,7 +1940,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) inode = mapping->host; if (S_ISBLK(inode->i_mode)) { struct block_device *bdev = I_BDEV(inode); - set_blocksize(bdev, p->old_block_size); + set_blocksize(bdev, old_block_size); blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL); } else { mutex_lock(&inode->i_mutex); -- 2.20.1