> seq_buf: Clear what a writer did not claim when a seq_buf overflows TL;DR: Commit message only: the claim that seq_buf_path() was "never exported, unlike the other writers" looks inaccurate, since several other writers are also unexported. The code and export look correct.
> seq_buf: Clear what a writer did not claim when a seq_buf overflows > > Using seq_buf_set_overflow() would leave the bytes between "len" > and "size" untouched, so if seq_buf_str() is used on an overflowed > seq_buf, those bytes may be exposed. For any paths that don't claim > partially written bytes, by setting "len = size" before calling > seq_buf_set_overflow(), wipe the unclaimed bytes. The seq_buf_puts() > and related APIs already claim those bytes now, so only the unclaimed > cases remain. A specific example of this was seq_buf_path() which uses > d_path() and would write to the tail before discovering it was out > of space, and would correctly mark a seq_buf as overflowed, but the > path fragment would be left over. > > Clear from len to the end of the buffer in seq_buf_set_overflow(), which > every overflow goes through, including seq_buf_commit() with a negative > count. > > Add a test that fills a seq_buf, leaves it too little room for a path, and > checks that nothing of the path is left in the buffer. The tests run > before > anything writable is mounted, so it takes its file from shmem. > > seq_buf_path() was never exported, unlike the other writers, so the > test failed to link as a module. Export it. > > 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, and the > test builds as a module (CONFIG_SEQ_BUF_KUNIT_TEST=m). > > Assisted-by: LLM > Reviewed-by: Andy Shevchenko <[email protected]> > Signed-off-by: Kees Cook <[email protected]> This isn't a bug, but is the comparison in "seq_buf_path() was never exported, unlike the other writers" accurate? In lib/seq_buf.c the only writers with an export are seq_buf_printf(), seq_buf_puts(), seq_buf_putc(), seq_buf_putmem() and seq_buf_putmem_hex() (plus seq_buf_do_printk(), which is not a writer). seq_buf_vprintf(), seq_buf_bprintf() and seq_buf_hex_dump() also write into a seq_buf and have no EXPORT_SYMBOL_GPL(). The reason for the export, that the new KUnit test calls seq_buf_path() and has to link with CONFIG_SEQ_BUF_KUNIT_TEST=m, looks correct. Could the sentence drop the "unlike the other writers" part, for example: seq_buf_path() was not exported, so the test failed to link as a module. Export it. --- AI reviewed your patch. Please fix the bug or email reply why it's not a bug. See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md CI run summary: https://github.com/kernel-patches/bpf/actions/runs/37096036516
