statmount: clean up unescaped option handling

Move common code from opt_array/opt_sec_array to helper.  This helper
does more than just unescape options, so rename to
statmount_opt_process().

Handle corner case of just a single character in options.

Rename some local variables to better describe their function.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Link: https://lore.kernel.org/r/20241120142732.55210-1-mszeredi@redhat.com
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/namespace.c b/fs/namespace.c
index 6b0a174..17563d8 100644 (file)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -5057,21 +5057,32 @@ static int statmount_mnt_opts(struct kstatmount *s, struct seq_file *seq)
        return 0;
 }
 
-static inline int statmount_opt_unescape(struct seq_file *seq, char *buf_start)
+static inline int statmount_opt_process(struct seq_file *seq, size_t start)
 {
-       char *buf_end, *opt_start, *opt_end;
+       char *buf_end, *opt_end, *src, *dst;
        int count = 0;
 
+       if (unlikely(seq_has_overflowed(seq)))
+               return -EAGAIN;
+
        buf_end = seq->buf + seq->count;
+       dst = seq->buf + start;
+       src = dst + 1;  /* skip initial comma */
+
+       if (src >= buf_end) {
+               seq->count = start;
+               return 0;
+       }
+
        *buf_end = '\0';
-       for (opt_start = buf_start + 1; opt_start < buf_end; opt_start = opt_end + 1) {
-               opt_end = strchrnul(opt_start, ',');
+       for (; src < buf_end; src = opt_end + 1) {
+               opt_end = strchrnul(src, ',');
                *opt_end = '\0';
-               buf_start += string_unescape(opt_start, buf_start, 0, UNESCAPE_OCTAL) + 1;
+               dst += string_unescape(src, dst, 0, UNESCAPE_OCTAL) + 1;
                if (WARN_ON_ONCE(++count == INT_MAX))
                        return -EOVERFLOW;
        }
-       seq->count = buf_start - 1 - seq->buf;
+       seq->count = dst - 1 - seq->buf;
        return count;
 }
 
@@ -5080,24 +5091,16 @@ static int statmount_opt_array(struct kstatmount *s, struct seq_file *seq)
        struct vfsmount *mnt = s->mnt;
        struct super_block *sb = mnt->mnt_sb;
        size_t start = seq->count;
-       char *buf_start;
        int err;
 
        if (!sb->s_op->show_options)
                return 0;
 
-       buf_start = seq->buf + start;
        err = sb->s_op->show_options(seq, mnt->mnt_root);
        if (err)
                return err;
 
-       if (unlikely(seq_has_overflowed(seq)))
-               return -EAGAIN;
-
-       if (seq->count == start)
-               return 0;
-
-       err = statmount_opt_unescape(seq, buf_start);
+       err = statmount_opt_process(seq, start);
        if (err < 0)
                return err;
 
@@ -5110,22 +5113,13 @@ static int statmount_opt_sec_array(struct kstatmount *s, struct seq_file *seq)
        struct vfsmount *mnt = s->mnt;
        struct super_block *sb = mnt->mnt_sb;
        size_t start = seq->count;
-       char *buf_start;
        int err;
 
-       buf_start = seq->buf + start;
-
        err = security_sb_show_options(seq, sb);
        if (!err)
                return err;
 
-       if (unlikely(seq_has_overflowed(seq)))
-               return -EAGAIN;
-
-       if (seq->count == start)
-               return 0;
-
-       err = statmount_opt_unescape(seq, buf_start);
+       err = statmount_opt_process(seq, start);
        if (err < 0)
                return err;