linux-ext4 - [PATCH v2 2/3] ext4: add support for 32-bit default reserved uid and gid values

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20250916-tune2fs-v2-2-d594dc7486f0@mit.edu>
Date: Tue, 16 Sep 2025 23:22:48 -0400
From: Theodore Ts'o via B4 Relay <devnull+tytso.mit.edu@...nel.org>
To: tytso@....edu
Cc: linux-ext4@...r.kernel.org, linux-api@...r.kernel.org
Subject: [PATCH v2 2/3] ext4: add support for 32-bit default reserved uid
 and gid values

From: Theodore Ts'o <tytso@....edu>

Support for specifying the default user id and group id that is
allowed to use the reserved block space was added way back when Linux
only supported 16-bit uid's and gid's.  (Yeah, that long ago.)  It's
not a commonly used feature, but let's add support for 32-bit user and
group id's.

Signed-off-by: Theodore Ts'o <tytso@....edu>
---
 fs/ext4/ext4.h  | 16 +++++++++++++++-
 fs/ext4/super.c |  8 ++++----
 2 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 01a6e2de7fc3ef0e20b039d3200b9c9bd656f59f..4bfcd5f0c74fda30db4009ee28fbee00a2f6b76f 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1442,7 +1442,9 @@ struct ext4_super_block {
 	__le16  s_encoding;		/* Filename charset encoding */
 	__le16  s_encoding_flags;	/* Filename charset encoding flags */
 	__le32  s_orphan_file_inum;	/* Inode for tracking orphan inodes */
-	__le32	s_reserved[94];		/* Padding to the end of the block */
+	__le16	s_def_resuid_hi;
+	__le16	s_def_resgid_hi;
+	__le32	s_reserved[93];		/* Padding to the end of the block */
 	__le32	s_checksum;		/* crc32c(superblock) */
 };
 
@@ -1812,6 +1814,18 @@ static inline int ext4_valid_inum(struct super_block *sb, unsigned long ino)
 		 ino <= le32_to_cpu(EXT4_SB(sb)->s_es->s_inodes_count));
 }
 
+static inline int ext4_get_resuid(struct ext4_super_block *es)
+{
+	return(le16_to_cpu(es->s_def_resuid) |
+	       (le16_to_cpu(es->s_def_resuid_hi) << 16));
+}
+
+static inline int ext4_get_resgid(struct ext4_super_block *es)
+{
+	return(le16_to_cpu(es->s_def_resgid) |
+	       (le16_to_cpu(es->s_def_resgid_hi) << 16));
+}
+
 /*
  * Returns: sbi->field[index]
  * Used to access an array element from the following sbi fields which require
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 94c98446c84f9a4614971d246ca7f001de610a8a..0256c8f7c6cee2b8d9295f2fa9a7acd904382e83 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2951,11 +2951,11 @@ static int _ext4_show_options(struct seq_file *seq, struct super_block *sb,
 	}
 
 	if (nodefs || !uid_eq(sbi->s_resuid, make_kuid(&init_user_ns, EXT4_DEF_RESUID)) ||
-	    le16_to_cpu(es->s_def_resuid) != EXT4_DEF_RESUID)
+	    ext4_get_resuid(es) != EXT4_DEF_RESUID)
 		SEQ_OPTS_PRINT("resuid=%u",
 				from_kuid_munged(&init_user_ns, sbi->s_resuid));
 	if (nodefs || !gid_eq(sbi->s_resgid, make_kgid(&init_user_ns, EXT4_DEF_RESGID)) ||
-	    le16_to_cpu(es->s_def_resgid) != EXT4_DEF_RESGID)
+	    ext4_get_resgid(es) != EXT4_DEF_RESGID)
 		SEQ_OPTS_PRINT("resgid=%u",
 				from_kgid_munged(&init_user_ns, sbi->s_resgid));
 	def_errors = nodefs ? -1 : le16_to_cpu(es->s_errors);
@@ -5270,8 +5270,8 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
 
 	ext4_set_def_opts(sb, es);
 
-	sbi->s_resuid = make_kuid(&init_user_ns, le16_to_cpu(es->s_def_resuid));
-	sbi->s_resgid = make_kgid(&init_user_ns, le16_to_cpu(es->s_def_resgid));
+	sbi->s_resuid = make_kuid(&init_user_ns, ext4_get_resuid(es));
+	sbi->s_resgid = make_kgid(&init_user_ns, ext4_get_resuid(es));
 	sbi->s_commit_interval = JBD2_DEFAULT_MAX_COMMIT_AGE * HZ;
 	sbi->s_min_batch_time = EXT4_DEF_MIN_BATCH_TIME;
 	sbi->s_max_batch_time = EXT4_DEF_MAX_BATCH_TIME;

-- 
2.51.0