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[2403:580d:fda1::299]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-82a07244071sm14734422b3a.6.2026.03.16.13.46.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 16 Mar 2026 13:46:12 -0700 (PDT) Message-ID: Date: Tue, 17 Mar 2026 07:16:06 +1030 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] btrfs: balance: fix null-ptr-deref in btrfs_may_alloc_data_chunk To: ZhengYuan Huang , dsterba@suse.com, clm@fb.com, bo.li.liu@oracle.com Cc: linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org, baijiaju1990@gmail.com, r33s3n6@gmail.com, zzzccc427@gmail.com, stable@vger.kernel.org References: <20260316134640.2605237-1-gality369@gmail.com> Content-Language: en-US From: Qu Wenruo Autocrypt: addr=wqu@suse.com; keydata= xsBNBFnVga8BCACyhFP3ExcTIuB73jDIBA/vSoYcTyysFQzPvez64TUSCv1SgXEByR7fju3o 8RfaWuHCnkkea5luuTZMqfgTXrun2dqNVYDNOV6RIVrc4YuG20yhC1epnV55fJCThqij0MRL 1NxPKXIlEdHvN0Kov3CtWA+R1iNN0RCeVun7rmOrrjBK573aWC5sgP7YsBOLK79H3tmUtz6b 9Imuj0ZyEsa76Xg9PX9Hn2myKj1hfWGS+5og9Va4hrwQC8ipjXik6NKR5GDV+hOZkktU81G5 gkQtGB9jOAYRs86QG/b7PtIlbd3+pppT0gaS+wvwMs8cuNG+Pu6KO1oC4jgdseFLu7NpABEB AAHNGFF1IFdlbnJ1byA8d3F1QHN1c2UuY29tPsLAlAQTAQgAPgIbAwULCQgHAgYVCAkKCwIE FgIDAQIeAQIXgBYhBC3fcuWlpVuonapC4cI9kfOhJf6oBQJnEXVgBQkQ/lqxAAoJEMI9kfOh Jf6o+jIH/2KhFmyOw4XWAYbnnijuYqb/obGae8HhcJO2KIGcxbsinK+KQFTSZnkFxnbsQ+VY fvtWBHGt8WfHcNmfjdejmy9si2jyy8smQV2jiB60a8iqQXGmsrkuR+AM2V360oEbMF3gVvim 2VSX2IiW9KERuhifjseNV1HLk0SHw5NnXiWh1THTqtvFFY+CwnLN2GqiMaSLF6gATW05/sEd V17MdI1z4+WSk7D57FlLjp50F3ow2WJtXwG8yG8d6S40dytZpH9iFuk12Sbg7lrtQxPPOIEU rpmZLfCNJJoZj603613w/M8EiZw6MohzikTWcFc55RLYJPBWQ+9puZtx1DopW2jOwE0EWdWB rwEIAKpT62HgSzL9zwGe+WIUCMB+nOEjXAfvoUPUwk+YCEDcOdfkkM5FyBoJs8TCEuPXGXBO Cl5P5B8OYYnkHkGWutAVlUTV8KESOIm/KJIA7jJA+Ss9VhMjtePfgWexw+P8itFRSRrrwyUf E+0WcAevblUi45LjWWZgpg3A80tHP0iToOZ5MbdYk7YFBE29cDSleskfV80ZKxFv6koQocq0 vXzTfHvXNDELAuH7Ms/WJcdUzmPyBf3Oq6mKBBH8J6XZc9LjjNZwNbyvsHSrV5bgmu/THX2n g/3be+iqf6OggCiy3I1NSMJ5KtR0q2H2Nx2Vqb1fYPOID8McMV9Ll6rh8S8AEQEAAcLAfAQY AQgAJgIbDBYhBC3fcuWlpVuonapC4cI9kfOhJf6oBQJnEXWBBQkQ/lrSAAoJEMI9kfOhJf6o cakH+QHwDszsoYvmrNq36MFGgvAHRjdlrHRBa4A1V1kzd4kOUokongcrOOgHY9yfglcvZqlJ qfa4l+1oxs1BvCi29psteQTtw+memmcGruKi+YHD7793zNCMtAtYidDmQ2pWaLfqSaryjlzR /3tBWMyvIeWZKURnZbBzWRREB7iWxEbZ014B3gICqZPDRwwitHpH8Om3eZr7ygZck6bBa4MU o1XgbZcspyCGqu1xF/bMAY2iCDcq6ULKQceuKkbeQ8qxvt9hVxJC2W3lHq8dlK1pkHPDg9wO JoAXek8MF37R8gpLoGWl41FIUb3hFiu3zhDDvslYM4BmzI18QgQTQnotJH8= In-Reply-To: <20260316134640.2605237-1-gality369@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 在 2026/3/17 00:16, ZhengYuan Huang 写道: > [BUG] > Running btrfs balance can trigger a null-ptr-deref before relocating a > data chunk when metadata corruption leaves a chunk in the chunk tree > without a corresponding block group in the in-memory cache: > > KASAN: null-ptr-deref in range [0x0000000000000088-0x000000000000008f] > RIP: 0010:btrfs_may_alloc_data_chunk+0x40/0x1c0 fs/btrfs/volumes.c:3601 > Call Trace: > __btrfs_balance fs/btrfs/volumes.c:4217 [inline] > btrfs_balance+0x2516/0x42b0 fs/btrfs/volumes.c:4604 > btrfs_ioctl_balance fs/btrfs/ioctl.c:3577 [inline] > btrfs_ioctl+0x25cf/0x5b90 fs/btrfs/ioctl.c:5313 > ... > > [CAUSE] > __btrfs_balance() iterates the on-disk chunk tree and passes the chunk > logical bytenr to btrfs_may_alloc_data_chunk() before relocating a data > chunk. That helper then queries the in-memory block group cache: > > cache = btrfs_lookup_block_group(fs_info, chunk_offset); > chunk_type = cache->flags; /* cache may be NULL */ > > On a corrupt image can contain a chunk item whose matching block group > item is missing, so no block group is ever inserted into the cache. In > that case btrfs_lookup_block_group() returns NULL. I'd say adding a proper chunk/bg mapping check is the root fix. Or you'll need to adhoc a lot of null pointer checks. > > The code only guards this with ASSERT(cache), which becomes a no-op when > CONFIG_BTRFS_ASSERT is disabled. The subsequent dereference of > cache->flags therefore crashes the kernel. > > [FIX] > Add a NULL check after btrfs_lookup_block_group() in > btrfs_may_alloc_data_chunk(). If the lookup fails, emit a btrfs_err() > message identifying the affected bytenr and return -EUCLEAN to report > filesystem corruption instead of dereferencing NULL. > > The caller already treats negative returns from > btrfs_may_alloc_data_chunk() as fatal errors, so balance aborts cleanly > and reports the corruption to userspace. > > Fixes: a6f93c71d412 ("Btrfs: avoid losing data raid profile when deleting a device") > Cc: stable@vger.kernel.org > Signed-off-by: ZhengYuan Huang > --- > fs/btrfs/volumes.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c > index 4958e074d420..4657b826b48b 100644 > --- a/fs/btrfs/volumes.c > +++ b/fs/btrfs/volumes.c > @@ -3597,7 +3597,12 @@ static int btrfs_may_alloc_data_chunk(struct btrfs_fs_info *fs_info, > u64 bytes_used; > u64 chunk_type; > > cache = btrfs_lookup_block_group(fs_info, chunk_offset); > - ASSERT(cache); > + if (!cache) { > + btrfs_err(fs_info, > + "balance: chunk at bytenr %llu has no corresponding block group", > + chunk_offset); > + return -EUCLEAN; > + } > chunk_type = cache->flags; > btrfs_put_block_group(cache); >