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Subject[PATCH 1/2] debugfs: Only clobber mode/uid/gid on remount if asked
Date
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.

# Don't change /sys/kernel/debug/ permissions.
mount -t debugfs none /mnt/foo

# Change /sys/kernel/debug/ mode and uid, but not gid.
mount -t debugfs -o uid=bar,mode=0750 none /mnt/baz

Signed-off-by: Brian Norris <briannorris@chromium.org>
---
I'm open to writing an LTP test case for this, if that seems like a good
idea.

fs/debugfs/inode.c | 29 ++++++++++++++++++++++-------
1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
index 3dcf0b8b4e93..1e36ce013631 100644
--- a/fs/debugfs/inode.c
+++ b/fs/debugfs/inode.c
@@ -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) {
@@ -145,22 +148,34 @@ 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 int 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.
+ */
+
+ if (!remount || opts->opts & BIT(Opt_mode)) {
+ inode->i_mode &= ~S_IALLUGO;
+ inode->i_mode |= opts->mode;
+ }
+
+ if (!remount || opts->opts & BIT(Opt_uid))
+ inode->i_uid = opts->uid;

- inode->i_uid = opts->uid;
- inode->i_gid = opts->gid;
+ if (!remount || opts->opts & BIT(Opt_gid))
+ inode->i_gid = opts->gid;

return 0;
}
@@ -175,7 +190,7 @@ static int debugfs_remount(struct super_block *sb, int *flags, char *data)
if (err)
goto fail;

- debugfs_apply_options(sb);
+ debugfs_apply_options(sb, true);

fail:
return err;
@@ -257,7 +272,7 @@ static int debug_fill_super(struct super_block *sb, void *data, int silent)
sb->s_op = &debugfs_super_operations;
sb->s_d_op = &debugfs_dops;

- debugfs_apply_options(sb);
+ debugfs_apply_options(sb, false);

return 0;

--
2.37.2.672.g94769d06f0-goog
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