[PATCH AUTOSEL 6.1 57/57] block: Deny writable memory mapping if block is read-only

Sasha Levin
2023-05-25T18:46:33Z

From: Loic Poulain <loic.poulain@linaro.org>

[ Upstream commit 69baa3a623fd2e58624f24f2f23d46f87b817c93 ]

User should not be able to write block device if it is read-only at
block level (e.g force_ro attribute). This is ensured in the regular
fops write operation (blkdev_write_iter) but not when writing via
user mapping (mmap), allowing user to actually write a read-only
block device via a PROT_WRITE mapping.

Example: This can lead to integrity issue of eMMC boot partition
(e.g mmcblk0boot0) which is read-only by default.

To fix this issue, simply deny shared writable mapping if the block
is readonly.

Note: Block remains writable if switch to read-only is performed
after the initial mapping, but this is expected behavior according
to commit a32e236eb93e ("Partially revert "block: fail op_is_write()
requests to read-only partitions"")'.

Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20230510074223.991297-1-loic.poulain@linaro.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
block/fops.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/block/fops.c b/block/fops.c
index e406aa605327e..6197d1c41652d 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -685,6 +685,16 @@ static long blkdev_fallocate(struct file *file, int mode, loff_t start,
return error;
}

+static int blkdev_mmap(struct file *file, struct vm_area_struct *vma)
+{
+ struct inode *bd_inode = bdev_file_inode(file);
+
+ if (bdev_read_only(I_BDEV(bd_inode)))
+ return generic_file_readonly_mmap(file, vma);
+
+ return generic_file_mmap(file, vma);
+}
+
const struct file_operations def_blk_fops = {
.open = blkdev_open,
.release = blkdev_close,
@@ -692,7 +702,7 @@ const struct file_operations def_blk_fops = {
.read_iter = blkdev_read_iter,
.write_iter = blkdev_write_iter,
.iopoll = iocb_bio_iopoll,
- .mmap = generic_file_mmap,
+ .mmap = blkdev_mmap,
.fsync = blkdev_fsync,
.unlocked_ioctl = blkdev_ioctl,
#ifdef CONFIG_COMPAT
--
2.39.2