6.12-stable review patch. If anyone has any objections, please let me know.
------------------
From: Qu Wenruo wqu@suse.com
[ Upstream commit 7e06de7c83a746e58d4701e013182af133395188 ]
[PROBLEM] Currently btrfs accepts any file path for its device, resulting some weird situation:
# ./mount_by_fd /dev/test/scratch1 /mnt/btrfs/
The program has the following source code:
#include <fcntl.h> #include <stdio.h> #include <sys/mount.h>
int main(int argc, char *argv[]) { int fd = open(argv[1], O_RDWR); char path[256]; snprintf(path, sizeof(path), "/proc/self/fd/%d", fd); return mount(path, argv[2], "btrfs", 0, NULL); }
Then we can have the following weird device path:
BTRFS: device fsid 2378be81-fe12-46d2-a9e8-68cf08dd98d5 devid 1 transid 7 /proc/self/fd/3 (253:2) scanned by mount_by_fd (18440)
Normally it's not a big deal, and later udev can trigger a device path rename. But if udev didn't trigger, the device path "/proc/self/fd/3" will show up in mtab.
[CAUSE] For filename "/proc/self/fd/3", it means the opened file descriptor 3. In above case, it's exactly the device we want to open, aka points to "/dev/test/scratch1" which is another symlink pointing to "/dev/dm-2".
Inside kernel we solve the mount source using LOOKUP_FOLLOW, which follows the symbolic link and grab the proper block device.
But inside btrfs we also save the filename into btrfs_device::name, and utilize that member to report our mount source, which leads to the above situation.
[FIX] Instead of unconditionally trust the path, check if the original file (not following the symbolic link) is inside "/dev/", if not, then manually lookup the path to its final destination, and use that as our device path.
This allows us to still use symbolic links, like "/dev/mapper/test-scratch" from LVM2, which is required for fstests runs with LVM2 setup.
And for really weird names, like the above case, we solve it to "/dev/dm-2" instead.
Reviewed-by: Filipe Manana fdmanana@suse.com Link: https://bugzilla.suse.com/show_bug.cgi?id=1230641 Reported-by: Fabian Vogt fvogt@suse.com Signed-off-by: Qu Wenruo wqu@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/btrfs/volumes.c | 87 +++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 86 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 5e75a4e3a5be5..5895397364aac 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -732,6 +732,78 @@ const u8 *btrfs_sb_fsid_ptr(const struct btrfs_super_block *sb) return has_metadata_uuid ? sb->metadata_uuid : sb->fsid; }
+/* + * We can have very weird soft links passed in. + * One example is "/proc/self/fd/<fd>", which can be a soft link to + * a block device. + * + * But it's never a good idea to use those weird names. + * Here we check if the path (not following symlinks) is a good one inside + * "/dev/". + */ +static bool is_good_dev_path(const char *dev_path) +{ + struct path path = { .mnt = NULL, .dentry = NULL }; + char *path_buf = NULL; + char *resolved_path; + bool is_good = false; + int ret; + + if (!dev_path) + goto out; + + path_buf = kmalloc(PATH_MAX, GFP_KERNEL); + if (!path_buf) + goto out; + + /* + * Do not follow soft link, just check if the original path is inside + * "/dev/". + */ + ret = kern_path(dev_path, 0, &path); + if (ret) + goto out; + resolved_path = d_path(&path, path_buf, PATH_MAX); + if (IS_ERR(resolved_path)) + goto out; + if (strncmp(resolved_path, "/dev/", strlen("/dev/"))) + goto out; + is_good = true; +out: + kfree(path_buf); + path_put(&path); + return is_good; +} + +static int get_canonical_dev_path(const char *dev_path, char *canonical) +{ + struct path path = { .mnt = NULL, .dentry = NULL }; + char *path_buf = NULL; + char *resolved_path; + int ret; + + if (!dev_path) { + ret = -EINVAL; + goto out; + } + + path_buf = kmalloc(PATH_MAX, GFP_KERNEL); + if (!path_buf) { + ret = -ENOMEM; + goto out; + } + + ret = kern_path(dev_path, LOOKUP_FOLLOW, &path); + if (ret) + goto out; + resolved_path = d_path(&path, path_buf, PATH_MAX); + ret = strscpy(canonical, resolved_path, PATH_MAX); +out: + kfree(path_buf); + path_put(&path); + return ret; +} + static bool is_same_device(struct btrfs_device *device, const char *new_path) { struct path old = { .mnt = NULL, .dentry = NULL }; @@ -1419,12 +1491,23 @@ struct btrfs_device *btrfs_scan_one_device(const char *path, blk_mode_t flags, bool new_device_added = false; struct btrfs_device *device = NULL; struct file *bdev_file; + char *canonical_path = NULL; u64 bytenr; dev_t devt; int ret;
lockdep_assert_held(&uuid_mutex);
+ if (!is_good_dev_path(path)) { + canonical_path = kmalloc(PATH_MAX, GFP_KERNEL); + if (canonical_path) { + ret = get_canonical_dev_path(path, canonical_path); + if (ret < 0) { + kfree(canonical_path); + canonical_path = NULL; + } + } + } /* * Avoid an exclusive open here, as the systemd-udev may initiate the * device scan which may race with the user's mount or mkfs command, @@ -1469,7 +1552,8 @@ struct btrfs_device *btrfs_scan_one_device(const char *path, blk_mode_t flags, goto free_disk_super; }
- device = device_list_add(path, disk_super, &new_device_added); + device = device_list_add(canonical_path ? : path, disk_super, + &new_device_added); if (!IS_ERR(device) && new_device_added) btrfs_free_stale_devices(device->devt, device);
@@ -1478,6 +1562,7 @@ struct btrfs_device *btrfs_scan_one_device(const char *path, blk_mode_t flags,
error_bdev_put: fput(bdev_file); + kfree(canonical_path);
return device; }