Commit 48fdd1e9 authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Pu Lehui
Browse files

bpf: avoid holding freeze_mutex during mmap operation 

stable inclusion
from stable-v6.6.80
commit 29cfda62ab4d92ab94123813db49ab76c1e61b29
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/IBSW0M
CVE: CVE-2025-21853

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=29cfda62ab4d

--------------------------------

[ Upstream commit bc27c52eea189e8f7492d40739b7746d67b65beb ]

We use map->freeze_mutex to prevent races between map_freeze() and
memory mapping BPF map contents with writable permissions. The way we
naively do this means we'll hold freeze_mutex for entire duration of all
the mm and VMA manipulations, which is completely unnecessary. This can
potentially also lead to deadlocks, as reported by syzbot in [0].

So, instead, hold freeze_mutex only during writeability checks, bump
(proactively) "write active" count for the map, unlock the mutex and
proceed with mmap logic. And only if something went wrong during mmap
logic, then undo that "write active" counter increment.

  [0] https://lore.kernel.org/bpf/678dcbc9.050a0220.303755.0066.GAE@google.com/



Fixes: fc970227 ("bpf: Add mmap() support for BPF_MAP_TYPE_ARRAY")
Reported-by: default avatar <syzbot+4dc041c686b7c816a71e@syzkaller.appspotmail.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20250129012246.1515826-2-andrii@kernel.org


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
Signed-off-by: default avatarPu Lehui <pulehui@huawei.com>
parent f1260b3a

kernel/bpf/syscall.c

+10 −7
Original line number Diff line number Diff line
@@ -883,7 +883,7 @@ static const struct vm_operations_struct bpf_map_default_vmops = { 
static int bpf_map_mmap(struct file *filp, struct vm_area_struct *vma)

{

	struct bpf_map *map = filp->private_data;

	int err;

	int err = 0;



	if (!map->ops->map_mmap || !IS_ERR_OR_NULL(map->record))

		return -ENOTSUPP;
@@ -907,7 +907,12 @@ static int bpf_map_mmap(struct file *filp, struct vm_area_struct *vma) 
			err = -EACCES;

			goto out;

		}

		bpf_map_write_active_inc(map);

	}

out:

	mutex_unlock(&map->freeze_mutex);

	if (err)

		return err;



	/* set default open/close callbacks */

	vma->vm_ops = &bpf_map_default_vmops;
@@ -924,13 +929,11 @@ static int bpf_map_mmap(struct file *filp, struct vm_area_struct *vma) 
		vm_flags_clear(vma, VM_MAYWRITE);



	err = map->ops->map_mmap(map, vma);

	if (err)

		goto out;



	if (err) {

		if (vma->vm_flags & VM_WRITE)

		bpf_map_write_active_inc(map);

out:

	mutex_unlock(&map->freeze_mutex);

			bpf_map_write_active_dec(map);

	}



	return err;

}