summaryrefslogtreecommitdiff
diff options
context:
space:
mode:
authorChristian Brauner <brauner@kernel.org>2024-03-23 17:11:20 +0100
committerChristian Brauner <brauner@kernel.org>2024-03-27 12:59:25 +0100
commit3ff56e285de5a375fbfab3c3f1af81bbd23db36d (patch)
treeafb41f5c9994aa19e82e9d893d79d9ca7a385ac4
parentddd65e19c60140673ea9f7249af0a672f1820623 (diff)
block: count BLK_OPEN_RESTRICT_WRITES openers
The original changes in v6.8 do allow for a block device to be reopened with BLK_OPEN_RESTRICT_WRITES provided the same holder is used as per bdev_may_open(). I think this has a bug. The first opener @f1 of that block device will set bdev->bd_writers to -1. The second opener @f2 using the same holder will pass the check in bdev_may_open() that bdev->bd_writers must not be greater than zero. The first opener @f1 now closes the block device and in bdev_release() will end up calling bdev_yield_write_access() which calls bdev_writes_blocked() and sets bdev->bd_writers to 0 again. Now @f2 holds a file to that block device which was opened with exclusive write access but bdev->bd_writers has been reset to 0. So now @f3 comes along and succeeds in opening the block device with BLK_OPEN_WRITE betraying @f2's request to have exclusive write access. This isn't a practical issue yet because afaict there's no codepath inside the kernel that reopenes the same block device with BLK_OPEN_RESTRICT_WRITES but it will be if there is. Fix this by counting the number of BLK_OPEN_RESTRICT_WRITES openers. So we only allow writes again once all BLK_OPEN_RESTRICT_WRITES openers are done. Link: https://lore.kernel.org/r/20240323-abtauchen-klauen-c2953810082d@brauner Fixes: ed5cc702d311 ("block: Add config option to not allow writing to mounted devices") Reviewed-by: Jan Kara <jack@suse.cz> Signed-off-by: Christian Brauner <brauner@kernel.org>
-rw-r--r--block/bdev.c6
1 files changed, 3 insertions, 3 deletions
diff --git a/block/bdev.c b/block/bdev.c
index ab9cae0e05f1..a1946a902df3 100644
--- a/block/bdev.c
+++ b/block/bdev.c
@@ -776,17 +776,17 @@ void blkdev_put_no_open(struct block_device *bdev)
static bool bdev_writes_blocked(struct block_device *bdev)
{
- return bdev->bd_writers == -1;
+ return bdev->bd_writers < 0;
}
static void bdev_block_writes(struct block_device *bdev)
{
- bdev->bd_writers = -1;
+ bdev->bd_writers--;
}
static void bdev_unblock_writes(struct block_device *bdev)
{
- bdev->bd_writers = 0;
+ bdev->bd_writers++;
}
static bool bdev_may_open(struct block_device *bdev, blk_mode_t mode)