On 2025/8/20 9:05, Steven Rostedt wrote:
> On Wed, 13 Aug 2025 02:30:44 +0000
> Tengda Wu <wuten...@huaweicloud.com> wrote:
>
>
>> Since the reader's hash is always tied to its file descriptor (fd),
>> the writer cannot directly manage the reader's hash. To fix this,
>> introduce a refcount for ftrace_hash, initialized to 1. The count
>> is incremented only when a reader opens it, and decremented when
>> either a reader or writer releases it, thereby controlling the timing
>> of ftrace_hash deallocation.
>
> Hmm, I think the code that the first patch touches is the issue here too.
>
> Instead of doing all these extra hacks, we should simply copy the hash for
> read too.
>
> That is, the real fix for both patches is this:
>
> -- Steve
>
> From: Steven Rostedt <rost...@goodmis.org>
> Subject: [PATCH] ftrace: Also allocate hash for reading of filter files
>
> Currently the reader of set_ftrace_filter and set_ftrace_notrace just adds
> the pointer to the global tracer hash to its iterator. Unlike the writer
> that allocates a copy of the hash, the reader keeps the pointer to the
> filter hashes. This is problematic because this pointer is static across
> function calls that release the locks that can update the global tracer
> hashes. This can cause UAF and similar bugs.
>
> Allocate the hash for reading the filter files like it is done for the
> writers. This not only fixes UAF bugs, but also makes the code a bit
> simpler as it doesn't have to differentiate when to free the iterator's
> hash between writers and readers.
Agreed. That is a much cleaner solution. I just tested this code and it
worked perfectly. Looking forward to getting it into the mainline soon.
-- Tengda
>
> Cc: sta...@vger.kernel.org
> Fixes: c20489dad156 ("ftrace: Assign iter->hash to filter or notrace hashes
> on seq read")
> Closes:
> https://lore.kernel.org/all/20250813023044.2121943-1-wuten...@huaweicloud.com/
> Reported-by: Tengda Wu <wuten...@huaweicloud.com>
> Signed-off-by: Steven Rostedt (Google) <rost...@goodmis.org>
> ---
> kernel/trace/ftrace.c | 16 +++++++---------
> 1 file changed, 7 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 00b76d450a89..f992a5eb878e 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -4661,13 +4661,14 @@ ftrace_regex_open(struct ftrace_ops *ops, int flag,
> } else {
> iter->hash = alloc_and_copy_ftrace_hash(size_bits,
> hash);
> }
> + } else {
> + iter->hash = alloc_and_copy_ftrace_hash(hash->size_bits, hash);
> + }
>
> - if (!iter->hash) {
> - trace_parser_put(&iter->parser);
> - goto out_unlock;
> - }
> - } else
> - iter->hash = hash;
> + if (!iter->hash) {
> + trace_parser_put(&iter->parser);
> + goto out_unlock;
> + }
>
> ret = 0;
>
> @@ -6543,9 +6544,6 @@ int ftrace_regex_release(struct inode *inode, struct
> file *file)
> ftrace_hash_move_and_update_ops(iter->ops, orig_hash,
> iter->hash, filter_hash);
> mutex_unlock(&ftrace_lock);
> - } else {
> - /* For read only, the hash is the ops hash */
> - iter->hash = NULL;
> }
>
> mutex_unlock(&iter->ops->func_hash->regex_lock);
