Re: [PATCH v4 08/11] seq_buf: Add seq_buf_init_append()
From: bot+bpf-ci@kernel.org
Date: 2026-10-03 04:34:01
Also in:
bpf, linux-doc, linux-hardening, linuxppc-dev, lkml, nvdimm
seq_buf: Add seq_buf_init_append()
TL;DR: Commit message only: it says seq_buf_init() sets the buffer size to 0 via seq_buf_clear(), but it resets the length, not the size. The code is not reported as buggy.
seq_buf: Add seq_buf_init_append() Several strlcat() call sites being converted to seq_buf need behavior seq_buf doesn't currently provide. The normal seq_buf_init() always sets the new buffer size to 0 via seq_buf_clear(). Code migrating from strlcat(buf, ...), which appends to whatever buf already contains, can't use seq_buf_init() without discarding that existing content. Add seq_buf_init_append(), which preserves the existing contents and positions the seq_buf to append after it. A buffer with no NUL within its size starts out overflowed, as strlcat() treats it as already truncated. Add KUnit tests for behavior coverage. Tests passed under qemu on ARCH=x86_64 with GCC 16.2.0 and CONFIG_KASAN=y, and on big-endian ARCH=s390 with GCC s390x-linux-gnu 16.2.0. Assisted-by: LLM Signed-off-by: Bill Wendling <morbo@google.com> Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Co-developed-by: Kees Cook <kees@kernel.org> Signed-off-by: Kees Cook <kees@kernel.org>
This isn't a bug in the code, but is the changelog accurate when it says
seq_buf_init() "always sets the new buffer size to 0 via seq_buf_clear()"?
seq_buf_init() stores the size it was given in s->size, and seq_buf_clear()
leaves s->size alone. It only resets the length and terminates the first
byte:
static inline void seq_buf_clear(struct seq_buf *s)
{
s->len = 0;
if (s->size)
s->buffer[0] = '\0';
}
Should the sentence say that seq_buf_init() always sets the length (s->len)
to 0 via seq_buf_clear(), rather than the buffer size?
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