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From:   Jeremy Bongio <bongiojp@gmail.com>
To:     Ted Tso <tytso@mit.edu>
Cc:     linux-ext4@vger.kernel.org, Jeremy Bongio <bongiojp@gmail.com>
Subject: [PATCH v4] tune2fs: Add support for get/set UUID ioctls.
Date:   Tue, 16 Aug 2022 13:52:14 -0700
Message-Id: <20220816205214.145632-1-bongiojp@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

When mounted, there is a race condition between changing the filesystem
UUID and changing other aspects of the filesystem, like mounting, resizing,
changing features, etc. Using these ioctls to get/set the UUID ensures the
filesystem is not being resized.

Signed-off-by: Jeremy Bongio <bongiojp@gmail.com>
---

Changes in v4:

Ioctl calls are now inline. handle_fsuuid() is removed.

Fsuuid is freed.

ext2fs_check_if_mounted() call replaced with ext2fs_check_mount_point()
to avoid redundancy.

I tested mounted and unmounted code paths.


 misc/tune2fs.c | 98 ++++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 79 insertions(+), 19 deletions(-)

diff --git a/misc/tune2fs.c b/misc/tune2fs.c
index 6c162ba5..d0cb90ae 100644
--- a/misc/tune2fs.c
+++ b/misc/tune2fs.c
@@ -82,11 +82,25 @@ extern int optind;
 #define FS_IOC_GETFSLABEL	_IOR(0x94, 49, char[FSLABEL_MAX])
 #endif
 
+struct fsuuid {
+	__u32   fsu_len;
+	__u32   fsu_flags;
+	__u8    fsu_uuid[];
+};
+
+#ifndef EXT4_IOC_GETFSUUID
+#define EXT4_IOC_GETFSUUID	_IOR('f', 44, struct fsuuid)
+#endif
+
+#ifndef EXT4_IOC_SETFSUUID
+#define EXT4_IOC_SETFSUUID	_IOW('f', 44, struct fsuuid)
+#endif
+
 extern int ask_yn(const char *string, int def);
 
 const char *program_name = "tune2fs";
 char *device_name;
-char *new_label, *new_last_mounted, *new_UUID;
+char *new_label, *new_last_mounted, *requested_uuid;
 char *io_options;
 static int c_flag, C_flag, e_flag, f_flag, g_flag, i_flag, l_flag, L_flag;
 static int m_flag, M_flag, Q_flag, r_flag, s_flag = -1, u_flag, U_flag, T_flag;
@@ -2102,7 +2116,7 @@ static void parse_tune2fs_options(int argc, char **argv)
 				open_flag = EXT2_FLAG_RW;
 				break;
 		case 'U':
-			new_UUID = optarg;
+			requested_uuid = optarg;
 			U_flag = 1;
 			open_flag = EXT2_FLAG_RW |
 				EXT2_FLAG_JOURNAL_DEV_OK;
@@ -3090,6 +3104,7 @@ int tune2fs_main(int argc, char **argv)
 	io_manager io_ptr, io_ptr_orig = NULL;
 	int rc = 0;
 	char default_undo_file[1] = { 0 };
+	char mntpt[PATH_MAX + 1];
 
 #ifdef ENABLE_NLS
 	setlocale(LC_MESSAGES, "");
@@ -3237,9 +3252,10 @@ retry_open:
 		goto closefs;
 	}
 
-	retval = ext2fs_check_if_mounted(device_name, &mount_flags);
+	retval = ext2fs_check_mount_point(device_name, &mount_flags,
+					mntpt, sizeof(mntpt));
 	if (retval) {
-		com_err("ext2fs_check_if_mount", retval,
+		com_err("ext2fs_check_mount_point", retval,
 			_("while determining whether %s is mounted."),
 			device_name);
 		rc = 1;
@@ -3454,6 +3470,10 @@ _("Warning: The journal is dirty. You may wish to replay the journal like:\n\n"
 		dgrp_t i;
 		char buf[SUPERBLOCK_SIZE] __attribute__ ((aligned(8)));
 		__u8 old_uuid[UUID_SIZE];
+		uuid_t new_uuid;
+		int fd = -1;
+		struct fsuuid *fsuuid = NULL;
+		errcode_t ret = -1;
 
 		if (ext2fs_has_feature_stable_inodes(fs->super)) {
 			fputs(_("Cannot change the UUID of this filesystem "
@@ -3507,25 +3527,62 @@ _("Warning: The journal is dirty. You may wish to replay the journal like:\n\n"
 				set_csum = 1;
 		}
 
-		memcpy(old_uuid, sb->s_uuid, UUID_SIZE);
-		if ((strcasecmp(new_UUID, "null") == 0) ||
-		    (strcasecmp(new_UUID, "clear") == 0)) {
-			uuid_clear(sb->s_uuid);
-		} else if (strcasecmp(new_UUID, "time") == 0) {
-			uuid_generate_time(sb->s_uuid);
-		} else if (strcasecmp(new_UUID, "random") == 0) {
-			uuid_generate(sb->s_uuid);
-		} else if (uuid_parse(new_UUID, sb->s_uuid)) {
+		if ((mount_flags & EXT2_MF_MOUNTED) &&
+			!(mount_flags & EXT2_MF_READONLY) && mntpt) {
+			fd = open(mntpt, O_RDONLY);
+			if (fd >= 0) {
+				fsuuid = malloc(sizeof(*fsuuid) + UUID_SIZE);
+				if (!fsuuid) {
+					close(fd);
+					fd = -1;
+				}
+			}
+		}
+
+		/* Get the filesystem uuid through the ioctl.
+		 * If the filesystem is offline or the ioctl is unavailable or
+		 * fails, fall back to directly modifiying the superblock.
+		 */
+		if (fd >= 0) {
+			fsuuid->fsu_len = UUID_SIZE;
+			fsuuid->fsu_flags = 0;
+			ret = ioctl(fd, EXT4_IOC_GETFSUUID, fsuuid);
+		}
+		if (ret)
+			memcpy(old_uuid, sb->s_uuid, UUID_SIZE);
+
+		if ((strcasecmp(requested_uuid, "null") == 0) ||
+		    (strcasecmp(requested_uuid, "clear") == 0)) {
+			uuid_clear(new_uuid);
+		} else if (strcasecmp(requested_uuid, "time") == 0) {
+			uuid_generate_time(new_uuid);
+		} else if (strcasecmp(requested_uuid, "random") == 0) {
+			uuid_generate(new_uuid);
+		} else if (uuid_parse(requested_uuid, new_uuid)) {
 			com_err(program_name, 0, "%s",
 				_("Invalid UUID format\n"));
 			rc = 1;
 			goto closefs;
 		}
-		ext2fs_init_csum_seed(fs);
-		if (set_csum) {
-			for (i = 0; i < fs->group_desc_count; i++)
-				ext2fs_group_desc_csum_set(fs, i);
-			fs->flags &= ~EXT2_FLAG_SUPER_ONLY;
+
+		/* Set the filesystem uuid through the ioctl or fallback to
+		 * directly modifying superblock.
+		 */
+		if (fd >= 0) {
+			fsuuid->fsu_len - UUID_SIZE;
+			fsuuid->fsu_flags = 0;
+			memcpy(&fsuuid->fsu_uuid, new_uuid, UUID_SIZE);
+			ret = ioctl(fd, EXT4_IOC_SETFSUUID, fsuuid);
+		}
+		if (ret) {
+			memcpy(sb->s_uuid, new_uuid, UUID_SIZE);
+			ext2fs_init_csum_seed(fs);
+			if (set_csum) {
+				for (i = 0; i < fs->group_desc_count; i++)
+					ext2fs_group_desc_csum_set(fs, i);
+				fs->flags &= ~EXT2_FLAG_SUPER_ONLY;
+			}
+			ext2fs_mark_super_dirty(fs);
 		}
 
 		/* If this is a journal dev, we need to copy UUID into jsb */
@@ -3550,7 +3607,10 @@ _("Warning: The journal is dirty. You may wish to replay the journal like:\n\n"
 				goto closefs;
 		}
 
-		ext2fs_mark_super_dirty(fs);
+		if (fd >= 0)
+			close(fd);
+		if (fsuuid)
+			free(fsuuid);
 	}
 
 	if (I_flag) {
-- 
2.37.1.595.g718a3a8f04-goog