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debugfs: Only clobber mode/uid/gid on remount if asked

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Users may have explicitly configured their debugfs permissions; we
shouldn't overwrite those just because a second mount appeared.

Only clobber if the options were provided at mount time.

Existing behavior:

  ## Pre-existing status: debugfs is 0755.
  # chmod 755 /sys/kernel/debug/
  # stat -c '%A' /sys/kernel/debug/
  drwxr-xr-x

  ## New mount sets kernel-default permissions:
  # mount -t debugfs none /mnt/foo
  # stat -c '%A' /mnt/foo
  drwx------

  ## Unexpected: the original mount changed permissions:
  # stat -c '%A' /sys/kernel/debug
  drwx------

New behavior:

  ## Pre-existing status: debugfs is 0755.
  # chmod 755 /sys/kernel/debug/
  # stat -c '%A' /sys/kernel/debug/
  drwxr-xr-x

  ## New mount inherits existing permissions:
  # mount -t debugfs none /mnt/foo
  # stat -c '%A' /mnt/foo
  drwxr-xr-x

  ## Expected: old mount is unchanged:
  # stat -c '%A' /sys/kernel/debug
  drwxr-xr-x

Full test cases are being submitted to LTP.

Signed-off-by: Brian Norris <briannorris@chromium.org>
Link: https://lore.kernel.org/r/20220912163042.v3.1.Icbd40fce59f55ad74b80e5d435ea233579348a78@changeid
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Brian Norris 2022-09-12 16:31:42 -07:00 committed by Greg Kroah-Hartman
parent 4abc996528
commit b8de524ce4
1 changed files with 30 additions and 7 deletions
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37
fs/debugfs/inode.c
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@ -82,6 +82,8 @@ struct debugfs_mount_opts {
kuid_t uid;
kgid_t gid;
umode_t mode;
/* Opt_* bitfield. */
unsigned int opts;
};
enum {
@ -111,6 +113,7 @@ static int debugfs_parse_options(char *data, struct debugfs_mount_opts *opts)
kgid_t gid;
char *p;
opts->opts = 0;
opts->mode = DEBUGFS_DEFAULT_MODE;
while ((p = strsep(&data, ",")) != NULL) {
@ -145,24 +148,44 @@ static int debugfs_parse_options(char *data, struct debugfs_mount_opts *opts)
* but traditionally debugfs has ignored all mount options
*/
}
opts->opts |= BIT(token);
}
return 0;
}
static int debugfs_apply_options(struct super_block *sb)
static void _debugfs_apply_options(struct super_block *sb, bool remount)
{
struct debugfs_fs_info *fsi = sb->s_fs_info;
struct inode *inode = d_inode(sb->s_root);
struct debugfs_mount_opts *opts = &fsi->mount_opts;
inode->i_mode &= ~S_IALLUGO;
inode->i_mode |= opts->mode;
/*
* On remount, only reset mode/uid/gid if they were provided as mount
* options.
*/
inode->i_uid = opts->uid;
inode->i_gid = opts->gid;
if (!remount || opts->opts & BIT(Opt_mode)) {
inode->i_mode &= ~S_IALLUGO;
inode->i_mode |= opts->mode;
}
return 0;
if (!remount || opts->opts & BIT(Opt_uid))
inode->i_uid = opts->uid;
if (!remount || opts->opts & BIT(Opt_gid))
inode->i_gid = opts->gid;
}
static void debugfs_apply_options(struct super_block *sb)
{
_debugfs_apply_options(sb, false);
}
static void debugfs_apply_options_remount(struct super_block *sb)
{
_debugfs_apply_options(sb, true);
}
static int debugfs_remount(struct super_block *sb, int *flags, char *data)
@ -175,7 +198,7 @@ static int debugfs_remount(struct super_block *sb, int *flags, char *data)
if (err)
goto fail;
debugfs_apply_options(sb);
debugfs_apply_options_remount(sb);
fail:
return err;