From: Domenico Andreoli Hibernation via snapshot device requires write permission to the swap block device, the one that more often (but not necessarily) is used to store the hibernation image. With this patch, such permissions are granted iff: 1) snapshot device config option is enabled 2) swap partition is used as snapshot device In other circumstance the swap device is not writable from userspace. In order to achieve this, every write attempt to a swap device is checked against the device configured as part of the uswsusp API [0] using a pointer to the inode struct in memory. If the swap device being written was not configured for snapshotting, the write request is denied. NOTE: this implementation works only for swap block devices, where the inode configured by swapon (which sets S_SWAPFILE) is the same used by SNAPSHOT_SET_SWAP_AREA. In case of swapfile, SNAPSHOT_SET_SWAP_AREA indeed receives the inode of the block device containing the filesystem where the swap files is located (+ offset in it) which is never passed to swapon and then has not the S_SWAPFILE set. As result, the swapfile itself (as a file) has never an option to be written from userspace. Instead it remains writable if accessed directly from the containing block device, which is always writeable from root. [0] Documentation/power/userland-swsusp.rst Signed-off-by: Domenico Andreoli Cc: "Rafael J. Wysocki" Cc: Pavel Machek Cc: Darrick J. Wong Cc: Christoph Hellwig Cc: viro@zeniv.linux.org.uk Cc: tytso@mit.edu Cc: len.brown@intel.com Cc: linux-pm@vger.kernel.org Cc: linux-mm@kvack.org Cc: linux-xfs@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org Cc: linux-kernel@vger.kernel.org --- fs/block_dev.c | 3 +-- include/linux/suspend.h | 6 ++++++ kernel/power/user.c | 14 +++++++++++++- 3 files changed, 20 insertions(+), 3 deletions(-) Index: b/include/linux/suspend.h =================================================================== --- a/include/linux/suspend.h +++ b/include/linux/suspend.h @@ -466,6 +466,12 @@ static inline bool system_entering_hiber static inline bool hibernation_available(void) { return false; } #endif /* CONFIG_HIBERNATION */ +#ifdef CONFIG_HIBERNATION_SNAPSHOT_DEV +int is_hibernate_snapshot_dev(const struct inode *); +#else +static inline int is_hibernate_snapshot_dev(const struct inode *i) { return 0; } +#endif + /* Hibernation and suspend events */ #define PM_HIBERNATION_PREPARE 0x0001 /* Going to hibernate */ #define PM_POST_HIBERNATION 0x0002 /* Hibernation finished */ Index: b/kernel/power/user.c =================================================================== --- a/kernel/power/user.c +++ b/kernel/power/user.c @@ -35,8 +35,14 @@ static struct snapshot_data { bool ready; bool platform_support; bool free_bitmaps; + struct inode *bd_inode; } snapshot_state; +int is_hibernate_snapshot_dev(const struct inode *bd_inode) +{ + return hibernation_available() && snapshot_state.bd_inode == bd_inode; +} + static int snapshot_open(struct inode *inode, struct file *filp) { struct snapshot_data *data; @@ -95,6 +101,7 @@ static int snapshot_open(struct inode *i data->frozen = false; data->ready = false; data->platform_support = false; + data->bd_inode = NULL; Unlock: unlock_system_sleep(); @@ -110,6 +117,7 @@ static int snapshot_release(struct inode swsusp_free(); data = filp->private_data; + data->bd_inode = NULL; free_all_swap_pages(data->swap); if (data->frozen) { pm_restore_gfp_mask(); @@ -202,6 +210,7 @@ struct compat_resume_swap_area { static int snapshot_set_swap_area(struct snapshot_data *data, void __user *argp) { + struct block_device *bdev; sector_t offset; dev_t swdev; @@ -232,9 +241,12 @@ static int snapshot_set_swap_area(struct data->swap = -1; return -EINVAL; } - data->swap = swap_type_of(swdev, offset, NULL); + data->swap = swap_type_of(swdev, offset, &bdev); if (data->swap < 0) return -ENODEV; + + data->bd_inode = bdev->bd_inode; + bdput(bdev); return 0; } Index: b/fs/block_dev.c =================================================================== --- a/fs/block_dev.c +++ b/fs/block_dev.c @@ -2023,8 +2023,7 @@ ssize_t blkdev_write_iter(struct kiocb * if (bdev_read_only(I_BDEV(bd_inode))) return -EPERM; - /* uswsusp needs write permission to the swap */ - if (IS_SWAPFILE(bd_inode) && !hibernation_available()) + if (IS_SWAPFILE(bd_inode) && !is_hibernate_snapshot_dev(bd_inode)) return -ETXTBSY; if (!iov_iter_count(from))