From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9F17D3EDE59; Tue, 12 May 2026 18:01:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778608876; cv=none; b=N3+nkRKcMYSsHpO7y5Fa5bwFc9TRrDGJ4O9/BYw4izteI/UQZ2/0GJHKihMonQlPSr5yWUWS30QeG3lfSc1qEAyEMD/OjgYUebmCZ0ngB9lld8G1hpwjDT+UI5v3+R1Oh87Vqg6YOickg1OlhDD6rFjwXqlhpFokr9cJ6N2XgsU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778608876; c=relaxed/simple; bh=w6lhtiV5v9KSiqNK1hmOXnhpMk2ao06DEkdmgCqu/0w=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=QJmSbSNkfwgTtppQSvPFZDypMcbNF01vo7QjqBKmcuSarSQ8m0AkJNHJCAQzAqZ/RvjsmVtmNBLspYfEg7uUcrk7d1tsvXnshlDPP8R4/N2j+q/bIySF78XUuV4Wmr8YpE8u+5gOcxtK/ZpxtlGpVTkMrW66dwoVsSznkYqu3Uw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=UzaNEwsN; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="UzaNEwsN" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 34A3AC2BCB0; Tue, 12 May 2026 18:01:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1778608876; bh=w6lhtiV5v9KSiqNK1hmOXnhpMk2ao06DEkdmgCqu/0w=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=UzaNEwsNaB8Xv+Gh7yKZrm4L79trkX1FmXwGW61fpzu4eWRIy86+0JmBAYkSNggm3 3y1cc3zZaPOU6sqW/bCn+2lNJlx0ld/Uzt656c08XZQrBu0ZHWTyk5Sb7gEQRg4idE UWZzFD2CEJIApyNTrynytc9NeMXac4uCSh5lDVpM= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Weiming Shi , Xiang Mei , Emil Tsalapatis , Alexei Starovoitov Subject: [PATCH 6.18 248/270] bpf: Fix use-after-free in arena_vm_close on fork Date: Tue, 12 May 2026 19:40:49 +0200 Message-ID: <20260512173943.660584735@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260512173938.452574370@linuxfoundation.org> References: <20260512173938.452574370@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Alexei Starovoitov commit 4fddde2a732de60bb97e3307d4eb69ac5f1d2b74 upstream. arena_vm_open() only bumps vml->mmap_count but never registers the child VMA in arena->vma_list. The vml->vma always points at the parent VMA, so after parent munmap the pointer dangles. If the child then calls bpf_arena_free_pages(), zap_pages() reads the stale vml->vma triggering use-after-free. Fix this by preventing the arena VMA from being inherited across fork with VM_DONTCOPY, and preventing VMA splits via the may_split callback. Also reject mremap with a .mremap callback returning -EINVAL. A same-size mremap(MREMAP_FIXED) on the full arena VMA reaches copy_vma() through the following path: check_prep_vma() - returns 0 early: new_len == old_len skips VM_DONTEXPAND check prep_move_vma() - vm_start == old_addr and vm_end == old_addr + old_len so may_split is never called move_vma() copy_vma_and_data() copy_vma() vm_area_dup() - copies vm_private_data (vml pointer) vm_ops->open() - bumps vml->mmap_count vm_ops->mremap() - returns -EINVAL, rollback unmaps new VMA The refcount ensures the rollback's arena_vm_close does not free the vml shared with the original VMA. Reported-by: Weiming Shi Reported-by: Xiang Mei Fixes: 317460317a02 ("bpf: Introduce bpf_arena.") Reviewed-by: Emil Tsalapatis Link: https://lore.kernel.org/r/20260413194245.21449-1-alexei.starovoitov@gmail.com Signed-off-by: Alexei Starovoitov Signed-off-by: Greg Kroah-Hartman --- kernel/bpf/arena.c | 19 ++++++++++++++++--- 1 file changed, 16 insertions(+), 3 deletions(-) --- a/kernel/bpf/arena.c +++ b/kernel/bpf/arena.c @@ -246,6 +246,16 @@ static void arena_vm_open(struct vm_area refcount_inc(&vml->mmap_count); } +static int arena_vm_may_split(struct vm_area_struct *vma, unsigned long addr) +{ + return -EINVAL; +} + +static int arena_vm_mremap(struct vm_area_struct *vma) +{ + return -EINVAL; +} + static void arena_vm_close(struct vm_area_struct *vma) { struct bpf_map *map = vma->vm_file->private_data; @@ -307,6 +317,8 @@ out: static const struct vm_operations_struct arena_vm_ops = { .open = arena_vm_open, + .may_split = arena_vm_may_split, + .mremap = arena_vm_mremap, .close = arena_vm_close, .fault = arena_vm_fault, }; @@ -376,10 +388,11 @@ static int arena_map_mmap(struct bpf_map arena->user_vm_end = vma->vm_end; /* * bpf_map_mmap() checks that it's being mmaped as VM_SHARED and - * clears VM_MAYEXEC. Set VM_DONTEXPAND as well to avoid - * potential change of user_vm_start. + * clears VM_MAYEXEC. Set VM_DONTEXPAND to avoid potential change + * of user_vm_start. Set VM_DONTCOPY to prevent arena VMA from + * being copied into the child process on fork. */ - vm_flags_set(vma, VM_DONTEXPAND); + vm_flags_set(vma, VM_DONTEXPAND | VM_DONTCOPY); vma->vm_ops = &arena_vm_ops; return 0; }