[Devel] [PATCH v2 VZ10 1/1] fs: namespace: transform mount flags to comma separated values
Vasileios Almpanis
vasileios.almpanis at virtuozzo.com
Tue Jun 2 17:44:18 MSK 2026
In legacy mount callpaths, userspace might pass mount options as
flags. These flags escape our checks in ve_devmnt_process allowing
devices to be mounted inside containers with options not specified in
the allowed field. Introduce helpers that take these flags and
already existing tables of flag -> string representation to construct
a comma separated value string from them, and append them to userspace
provided data. Then pass this string to parse_monolithic_mount_data
enforcing the same checks symmetrically in both mount and fsconfig
syscalls.
In the remount path, run legacy_merge_mount_data() before
ve_devmnt_process() so container device mount policy sees MS_* flags
from the legacy mount(2) API, not only the user-supplied option string.
Keep ve_prepare_mount_options() for legacy parsers that do not use
generic_parse_monolithic().
https://virtuozzo.atlassian.net/browse/VSTOR-132330
Signed-off-by: Vasileios Almpanis <vasileios.almpanis at virtuozzo.com>
Feature: ve: ve generic structures
---
Changes since v1:
- Replace open-coded flag loops with append_entry() helper (pointer-
advancing style) that unifies the comma-insert-copy pattern across
all three call sites
- Rework legacy_merge_mount_data() to allocate the page upfront, write
user data first then append sb flags via vfs_format_sb_flags(); this
eliminates the intermediate flags_buf[128], the total size calculation,
and the +1/+2 arithmetic
- Fix inconsistent error code: replace -EINVAL with -ENOSPC for the
buffer-too-small case
- Add comment on FS_BINARY_MOUNTDATA explaining why those filesystems
are skipped
- Add blank line before return in legacy_merge_mount_data()
- Remove excess blank line after parse_monolithic_mount_data() in
do_remount()
fs/fs_context.c | 114 ++++++++++++++++++++++++++++++++++++++++++++++++
fs/internal.h | 8 ++++
fs/namespace.c | 32 +++++++++++---
3 files changed, 147 insertions(+), 7 deletions(-)
diff --git a/fs/fs_context.c b/fs/fs_context.c
index 76f34f3d468e..ae6ea684d596 100644
--- a/fs/fs_context.c
+++ b/fs/fs_context.c
@@ -81,6 +81,120 @@ static int vfs_parse_sb_flag(struct fs_context *fc, const char *key)
return -ENOPARAM;
}
+#ifdef CONFIG_VE
+/*
+ * Append s to the buffer at dst, preceded by a comma if len > 0.
+ * cap is the total buffer capacity (excluding the null terminator slot).
+ * Updates *len and returns the new write position, or ERR_PTR(-ENOSPC).
+ */
+static char *append_entry(char *dst, size_t *len, size_t cap, const char *s)
+{
+ size_t s_len = strlen(s);
+ size_t write_chars = (*len > 0) + s_len;
+
+ if (*len + write_chars > cap)
+ return ERR_PTR(-ENOSPC);
+ if (*len)
+ *dst++ = ',';
+ memcpy(dst, s, s_len);
+ *len += write_chars;
+ return dst + s_len;
+}
+
+/*
+ * Append fc->sb_flags as comma-separated option names into [*dstp, cap).
+ * Updates *dstp and *lenp on success.
+ * Matches vfs_parse_sb_flag() / common_{set,clear}_sb_flag tables.
+ */
+static int vfs_format_sb_flags(struct fs_context *fc,
+ char **dstp, size_t *lenp, size_t cap)
+{
+ const struct constant_table *p;
+ unsigned int flags = fc->sb_flags;
+ unsigned int mask = fc->sb_flags_mask;
+ char *dst = *dstp;
+
+ for (p = common_set_sb_flag; p->name; p++) {
+ if (!(flags & p->value))
+ continue;
+ dst = append_entry(dst, lenp, cap, p->name);
+ if (IS_ERR(dst))
+ return PTR_ERR(dst);
+ }
+
+ for (p = common_clear_sb_flag; p->name; p++) {
+ if (!(mask & p->value) || (flags & p->value))
+ continue;
+ dst = append_entry(dst, lenp, cap, p->name);
+ if (IS_ERR(dst))
+ return PTR_ERR(dst);
+ }
+
+ *dstp = dst;
+ return 0;
+}
+
+/*
+ * For legacy mount(2), MS_* mount flags are folded into fc->sb_flags and are
+ * not present in the monolithic data string. Build a page with user data
+ * followed by those flags for ve_devmnt checks in vfs_parse_monolithic_sep.
+ *
+ * Returns @data when nothing needs to be added, a new page otherwise, or
+ * ERR_PTR() on failure. The caller must free_page() when the result != @data.
+ */
+void *legacy_merge_mount_data(struct fs_context *fc, void *data)
+{
+ struct ve_struct *ve = get_exec_env();
+ char *page, *dst;
+ size_t len = 0;
+ int err;
+
+ if (ve_is_super(ve))
+ return data;
+
+ if (!fc->fs_type || !(fc->fs_type->fs_flags & FS_REQUIRES_DEV))
+ return data;
+
+ /*
+ * Filesystems with binary mount data (e.g. btrfs) bypass option
+ * string parsing entirely, so our checks cannot apply here.
+ */
+ if (fc->fs_type->fs_flags & FS_BINARY_MOUNTDATA)
+ return data;
+
+ page = (char *)__get_free_page(GFP_KERNEL);
+ if (!page)
+ return ERR_PTR(-ENOMEM);
+
+ dst = page;
+
+ if (data && *(char *)data) {
+ dst = append_entry(dst, &len, PAGE_SIZE - 1, (char *)data);
+ if (IS_ERR(dst)) {
+ err = PTR_ERR(dst);
+ goto err_free;
+ }
+ }
+
+ err = vfs_format_sb_flags(fc, &dst, &len, PAGE_SIZE - 1);
+ if (err)
+ goto err_free;
+
+ if (!len) {
+ free_page((unsigned long)page);
+ return data;
+ }
+
+ *dst = '\0';
+
+ return page;
+
+err_free:
+ free_page((unsigned long)page);
+ return ERR_PTR(err);
+}
+#endif /* CONFIG_VE */
+
/**
* vfs_parse_fs_param_source - Handle setting "source" via parameter
* @fc: The filesystem context to modify
diff --git a/fs/internal.h b/fs/internal.h
index 0064345cb9d0..120c239df394 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -46,6 +46,14 @@ extern void __init chrdev_init(void);
*/
extern const struct fs_context_operations legacy_fs_context_ops;
extern int parse_monolithic_mount_data(struct fs_context *, void *);
+#ifdef CONFIG_VE
+void *legacy_merge_mount_data(struct fs_context *fc, void *data);
+#else
+static inline void *legacy_merge_mount_data(struct fs_context *fc, void *data)
+{
+ return data;
+}
+#endif
extern void vfs_clean_context(struct fs_context *fc);
extern int finish_clean_context(struct fs_context *fc);
diff --git a/fs/namespace.c b/fs/namespace.c
index acd4507e1247..b2defe2006ca 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -3295,6 +3295,7 @@ static int do_remount(struct path *path, int ms_flags, int sb_flags,
struct super_block *sb = path->mnt->mnt_sb;
struct mount *mnt = real_mount(path->mnt);
struct fs_context *fc;
+ void *mnt_data = NULL;
if (!check_mnt(mnt))
return -EINVAL;
@@ -3315,13 +3316,17 @@ static int do_remount(struct path *path, int ms_flags, int sb_flags,
*/
fc->oldapi = true;
- err = ve_prepare_mount_options(fc, data);
- if (err) {
- put_fs_context(fc);
- return err;
+ mnt_data = legacy_merge_mount_data(fc, data);
+ if (IS_ERR(mnt_data)) {
+ err = PTR_ERR(mnt_data);
+ goto err;
}
- err = parse_monolithic_mount_data(fc, data);
+ err = ve_prepare_mount_options(fc, mnt_data);
+ if (err)
+ goto free_mnt_data;
+
+ err = parse_monolithic_mount_data(fc, mnt_data);
if (!err) {
down_write(&sb->s_umount);
err = -EPERM;
@@ -3338,6 +3343,10 @@ static int do_remount(struct path *path, int ms_flags, int sb_flags,
mnt_warn_timestamp_expiry(path, &mnt->mnt);
+free_mnt_data:
+ if (mnt_data && mnt_data != data)
+ free_page((unsigned long)mnt_data);
+err:
put_fs_context(fc);
return err;
}
@@ -3774,8 +3783,17 @@ static int do_new_mount(struct path *path, const char *fstype, int sb_flags,
subtype, strlen(subtype));
if (!err && name)
err = vfs_parse_fs_string(fc, "source", name, strlen(name));
- if (!err)
- err = parse_monolithic_mount_data(fc, data);
+ if (!err) {
+ void *mnt_data = legacy_merge_mount_data(fc, data);
+
+ if (IS_ERR(mnt_data)) {
+ err = PTR_ERR(mnt_data);
+ } else {
+ err = parse_monolithic_mount_data(fc, mnt_data);
+ if (mnt_data != data)
+ free_page((unsigned long)mnt_data);
+ }
+ }
if (!err && !mount_capable(fc))
err = -EPERM;
if (!err)
--
2.43.0
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