From: Andrii Nakryiko <andrii@kernel.org> stable inclusion from stable-v6.6.80 commit fc01ba097319ae2033f118da3075bd783f4a08e9 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=... -------------------------------- [ Upstream commit 98671a0fd1f14e4a518ee06b19037c20014900eb ] For all BPF maps we ensure that VM_MAYWRITE is cleared when memory-mapping BPF map contents as initially read-only VMA. This is because in some cases BPF verifier relies on the underlying data to not be modified afterwards by user space, so once something is mapped read-only, it shouldn't be re-mmap'ed as read-write. As such, it's not necessary to check VM_MAYWRITE in bpf_map_mmap() and map->ops->map_mmap() callbacks: VM_WRITE should be consistently set for read-write mappings, and if VM_WRITE is not set, there is no way for user space to upgrade read-only mapping to read-write one. This patch cleans up this VM_WRITE vs VM_MAYWRITE handling within bpf_map_mmap(), which is an entry point for any BPF map mmap()-ing logic. We also drop unnecessary sanitization of VM_MAYWRITE in BPF ringbuf's map_mmap() callback implementation, as it is already performed by common code in bpf_map_mmap(). Note, though, that in bpf_map_mmap_{open,close}() callbacks we can't drop VM_MAYWRITE use, because it's possible (and is outside of subsystem's control) to have initially read-write memory mapping, which is subsequently dropped to read-only by user space through mprotect(). In such case, from BPF verifier POV it's read-write data throughout the lifetime of BPF map, and is counted as "active writer". But its VMAs will start out as VM_WRITE|VM_MAYWRITE, then mprotect() can change it to just VM_MAYWRITE (and no VM_WRITE), so when its finally munmap()'ed and bpf_map_mmap_close() is called, vm_flags will be just VM_MAYWRITE, but we still need to decrement active writer count with bpf_map_write_active_dec() as it's still considered to be a read-write mapping by the rest of BPF subsystem. Similar reasoning applies to bpf_map_mmap_open(), which is called whenever mmap(), munmap(), and/or mprotect() forces mm subsystem to split original VMA into multiple discontiguous VMAs. Memory-mapping handling is a bit tricky, yes. Cc: Jann Horn <jannh@google.com> Cc: Suren Baghdasaryan <surenb@google.com> Cc: Shakeel Butt <shakeel.butt@linux.dev> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/r/20250129012246.1515826-1-andrii@kernel.org Signed-off-by: Alexei Starovoitov <ast@kernel.org> Stable-dep-of: bc27c52eea18 ("bpf: avoid holding freeze_mutex during mmap operation") Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Pu Lehui <pulehui@huawei.com> --- kernel/bpf/ringbuf.c | 4 ---- kernel/bpf/syscall.c | 10 ++++++++-- 2 files changed, 8 insertions(+), 6 deletions(-) diff --git a/kernel/bpf/ringbuf.c b/kernel/bpf/ringbuf.c index 00688545742f..6aff5ee483b6 100644 --- a/kernel/bpf/ringbuf.c +++ b/kernel/bpf/ringbuf.c @@ -268,8 +268,6 @@ static int ringbuf_map_mmap_kern(struct bpf_map *map, struct vm_area_struct *vma /* allow writable mapping for the consumer_pos only */ if (vma->vm_pgoff != 0 || vma->vm_end - vma->vm_start != PAGE_SIZE) return -EPERM; - } else { - vm_flags_clear(vma, VM_MAYWRITE); } /* remap_vmalloc_range() checks size and offset constraints */ return remap_vmalloc_range(vma, rb_map->rb, @@ -289,8 +287,6 @@ static int ringbuf_map_mmap_user(struct bpf_map *map, struct vm_area_struct *vma * position, and the ring buffer data itself. */ return -EPERM; - } else { - vm_flags_clear(vma, VM_MAYWRITE); } /* remap_vmalloc_range() checks size and offset constraints */ return remap_vmalloc_range(vma, rb_map->rb, vma->vm_pgoff + RINGBUF_PGOFF); diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index f8edda3bf396..f79b8915d8c8 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -913,15 +913,21 @@ static int bpf_map_mmap(struct file *filp, struct vm_area_struct *vma) vma->vm_ops = &bpf_map_default_vmops; vma->vm_private_data = map; vm_flags_clear(vma, VM_MAYEXEC); + /* If mapping is read-only, then disallow potentially re-mapping with + * PROT_WRITE by dropping VM_MAYWRITE flag. This VM_MAYWRITE clearing + * means that as far as BPF map's memory-mapped VMAs are concerned, + * VM_WRITE and VM_MAYWRITE and equivalent, if one of them is set, + * both should be set, so we can forget about VM_MAYWRITE and always + * check just VM_WRITE + */ if (!(vma->vm_flags & VM_WRITE)) - /* disallow re-mapping with PROT_WRITE */ vm_flags_clear(vma, VM_MAYWRITE); err = map->ops->map_mmap(map, vma); if (err) goto out; - if (vma->vm_flags & VM_MAYWRITE) + if (vma->vm_flags & VM_WRITE) bpf_map_write_active_inc(map); out: mutex_unlock(&map->freeze_mutex); -- 2.34.1