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ext4: only update tune mount options when requested

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EXT4_IOC_SET_TUNE_SB_PARAM uses set_flags to indicate which superblock
fields the caller wants to update. ext4_sb_setparams() checks set_flags
before updating the other supported fields, but always copied mount_opts
into the on-disk s_mount_opts field.

As a result, callers that do not set EXT4_TUNE_FL_MOUNT_OPTS can still
clear or alter the on-disk default mount options through their unused
mount_opts buffer. This can affect subsequent mounts by changing the
filesystem's stored default mount options.

Only copy mount_opts into s_mount_opts when EXT4_TUNE_FL_MOUNT_OPTS is set,
matching the set_flags semantics used by the other tuneable superblock
fields.

Cc: stable@kernel.org
Fixes: 04a91570ac ("ext4: implemet new ioctls to set and get superblock parameters")
Signed-off-by: guzebing <guzebing1612@gmail.com>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Link: https://patch.msgid.link/20260810151200.1405562-1-guzebing1612@gmail.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
guzebing 2026-08-10 23:12:00 +08:00 committed by Theodore Ts'o
parent 93f51579e7
commit 981eec6c30
1 changed files with 2 additions and 1 deletions
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3
fs/ext4/ioctl.c
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@ -1362,7 +1362,8 @@ static void ext4_sb_setparams(struct ext4_sb_info *sbi,
es->s_encoding = cpu_to_le16(params->encoding);
if (params->set_flags & EXT4_TUNE_FL_ENCODING_FLAGS)
es->s_encoding_flags = cpu_to_le16(params->encoding_flags);
strscpy_pad(es->s_mount_opts, params->mount_opts);
if (params->set_flags & EXT4_TUNE_FL_MOUNT_OPTS)
strscpy_pad(es->s_mount_opts, params->mount_opts);
if (params->set_flags & EXT4_TUNE_FL_EDIT_FEATURES) {
es->s_feature_compat |=
cpu_to_le32(params->set_feature_compat_mask);