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From: Thomas Gleixner <tglx@kernel.org>
To: Andrii Nakryiko <andrii@kernel.org>, akpm@linux-foundation.org,
 linux-mm@kvack.org
Cc: linux-fsdevel@vger.kernel.org, bpf@vger.kernel.org, surenb@google.com,
 shakeel.butt@linux.dev, Andrii Nakryiko <andrii@kernel.org>,
 syzbot+4e70c8e0a2017b432f7a@syzkaller.appspotmail.com,
 syzbot+237b5b985b78c1da9600@syzkaller.appspotmail.com, Peter Zijlstra
 <peterz@infradead.org>, Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: [BUG] [PATCH v2 mm-stable] procfs: avoid fetching build ID while
 holding VMA lock
In-Reply-To: <20260129215340.3742283-1-andrii@kernel.org>
References: <20260129215340.3742283-1-andrii@kernel.org>
Date: Tue, 10 Feb 2026 19:41:12 +0100
Message-ID: <87qzqsa1br.ffs@tglx>
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On Thu, Jan 29 2026 at 13:53, Andrii Nakryiko wrote:
>  	/* unlock vma or mmap_lock, and put mm_struct before copying data to user */
>  	query_vma_teardown(&lock_ctx);
>  	mmput(mm);
>  
> +	if (karg.build_id_size) {
> +		__u32 build_id_sz;
> +
> +		if (vm_file)
> +			err = build_id_parse_file(vm_file, build_id_buf, &build_id_sz);
> +		else
> +			err = -ENOENT;
> +		if (err) {
> +			karg.build_id_size = 0;
> +		} else {
> +			if (karg.build_id_size < build_id_sz) {
> +				err = -ENAMETOOLONG;
> +				goto out;

Introduces a double mmput() here.

> +			}
> +			karg.build_id_size = build_id_sz;
> +		}
> +	}
> +
> +	if (vm_file)
> +		fput(vm_file);
> +
>  	if (karg.vma_name_size && copy_to_user(u64_to_user_ptr(karg.vma_name_addr),
>  					       name, karg.vma_name_size)) {
>  		kfree(name_buf);
> @@ -798,6 +808,8 @@ static int do_procmap_query(struct mm_struct *mm, void __user *uarg)
>  out:
>  	query_vma_teardown(&lock_ctx);
>  	mmput(mm);
> +	if (vm_file)
> +		fput(vm_file);
>  	kfree(name_buf);
>  	return err;

See:

        https://lore.kernel.org/all/698aaf3c.050a0220.3b3015.0088.GAE@google.com/T/#u

Thanks

        tglx