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Sat, 15 Aug 2026 15:14:30 -0700 (PDT) Message-ID: <33963533-344c-4f52-8ef7-4c10979f3153@suse.com> Date: Sun, 16 Aug 2026 07:44:24 +0930 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 v2] btrfs: allow idmapped DEFRAG ioctls To: Tao Cui , clm@fb.com, dsterba@suse.com, sforshee@kernel.org Cc: josef@toxicpanda.com, brauner@kernel.org, linux-btrfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Tao Cui References: <20260815132259.3935817-1-cui.tao@linux.dev> 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: <20260815132259.3935817-1-cui.tao@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 在 2026/8/15 22:52, Tao Cui 写道: > From: Tao Cui > > btrfs_ioctl_defrag() checks MAY_WRITE against nop_mnt_idmap, so on an > idmapped mount the owner comparison uses the caller's fsuid against the > raw on-disk uid and the ioctl fails with -EPERM even for the file's > owner. Pass the mount idmap down so defrag works on idmapped mounts. > > The check, added in 616d374efa23 ("btrfs: allow defrag on a file opened > read-only that has rw permissions"), is not a privilege gate. It only > tests whether the file could have been opened for writing, and a user > who owns the file on the idmapped mount can already open it O_RDWR, > write() to it or fallocate() it. Defragmenting a regular file only > rearranges the caller's own extents; there is nothing it can rewrite > that the caller could not rewrite anyway. Whole-subvolume defrag on a > directory keeps its capable(CAP_SYS_ADMIN) requirement, and the > !capable() guard around this check is left as is. > > FIDEDUPERANGE already works this way for unprivileged callers: > may_dedupe_file() in fs/remap_range.c compares the inode owner through > file_mnt_idmap(file) and falls back to inode_permission() with the same > idmap, and dedupe can rewrite one file's extents from another file's > contents, which is a stronger operation than defrag. > > On regular mounts file_mnt_idmap() is nop_mnt_idmap and nothing > changes. > > Signed-off-by: Tao Cui Reviewed-by: Qu Wenruo > --- > v2: rewrite the commit message to explain why defrag is safe for > idmapped users (Seth Forshee); the code is unchanged. > --- > fs/btrfs/ioctl.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c > index 72bc9d4f7708..607329dedd50 100644 > --- a/fs/btrfs/ioctl.c > +++ b/fs/btrfs/ioctl.c > @@ -2458,7 +2458,7 @@ static int btrfs_ioctl_defrag(struct file *file, void __user *argp) > * running and allows defrag on files open in read-only mode. > */ > if (!capable(CAP_SYS_ADMIN) && > - inode_permission(&nop_mnt_idmap, inode, MAY_WRITE)) { > + inode_permission(file_mnt_idmap(file), inode, MAY_WRITE)) { > ret = -EPERM; > goto out; > }