From ad1e4f74c072eaa2c6d77dd710db31aafecd614f Mon Sep 17 00:00:00 2001 From: Domenico Andreoli Date: Tue, 19 May 2020 20:14:10 +0200 Subject: [PATCH] PM: hibernate: Restrict writes to the resume device 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 resume device In other circumstances 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 resuming, 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 swap file, SNAPSHOT_SET_SWAP_AREA indeed receives the inode of the block device containing the filesystem where the swap file is located (+ offset in it) which is never passed to swapon and then has not set S_SWAPFILE. As result, the swap file 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 v2: - rename is_hibernate_snapshot_dev() to is_hibernate_resume_dev() - fix description so to correctly refer to the resume device Signed-off-by: Domenico Andreoli Acked-by: Darrick J. Wong Signed-off-by: Rafael J. Wysocki --- fs/block_dev.c | 3 +-- include/linux/suspend.h | 6 ++++++ kernel/power/user.c | 14 +++++++++++++- 3 files changed, 20 insertions(+), 3 deletions(-) diff --git a/fs/block_dev.c b/fs/block_dev.c index 93672c3f1c78..608a7b9173f4 100644 --- a/fs/block_dev.c +++ b/fs/block_dev.c @@ -2023,8 +2023,7 @@ ssize_t blkdev_write_iter(struct kiocb *iocb, struct iov_iter *from) 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_resume_dev(bd_inode)) return -ETXTBSY; if (!iov_iter_count(from)) diff --git a/include/linux/suspend.h b/include/linux/suspend.h index 4fcc6fd0cbd6..b960098acfb0 100644 --- a/include/linux/suspend.h +++ b/include/linux/suspend.h @@ -466,6 +466,12 @@ static inline bool system_entering_hibernation(void) { return false; } static inline bool hibernation_available(void) { return false; } #endif /* CONFIG_HIBERNATION */ +#ifdef CONFIG_HIBERNATION_SNAPSHOT_DEV +int is_hibernate_resume_dev(const struct inode *); +#else +static inline int is_hibernate_resume_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 */ diff --git a/kernel/power/user.c b/kernel/power/user.c index 98548d1cf8a6..d5eedc2baa2a 100644 --- 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_resume_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 *inode, struct file *filp) 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 *inode, struct file *filp) 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 snapshot_data *data, 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; }