Date: Sat, 21 Oct 2017 21:40:14 +0200 From: Nicolas Belouin <nicolas@...ouin.fr> To: Nick Kralevich <nnk@...gle.com> CC: Alexander Viro <viro@...iv.linux.org.uk>, linux-fsdevel@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>, linux-api@...r.kernel.org, kernel-hardening@...ts.openwall.com Subject: Re: [PATCH] fs: Use CAP_DAC_OVERRIDE to allow for file dedupe On October 21, 2017 4:08:31 PM GMT+02:00, Nick Kralevich <nnk@...gle.com> wrote: >On Sat, Oct 21, 2017 at 6:28 AM, Nicolas Belouin <nicolas@...ouin.fr> >wrote: >> In its current implementation the check is against CAP_SYS_ADMIN, >> however this capability is bloated and inapropriate for this use. >> Indeed the check aims to avoid dedupe against non writable files, >> falling directly in the use case of CAP_DAC_OVERRIDE. >> >> Signed-off-by: Nicolas Belouin <nicolas@...ouin.fr> >> --- >> fs/read_write.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/fs/read_write.c b/fs/read_write.c >> index f0d4b16873e8..43cc7e84e29e 100644 >> --- a/fs/read_write.c >> +++ b/fs/read_write.c >> @@ -1965,7 +1965,7 @@ int vfs_dedupe_file_range(struct file *file, >struct file_dedupe_range *same) >> u64 len; >> int i; >> int ret; >> - bool is_admin = capable(CAP_SYS_ADMIN); >> + bool is_admin = capable(CAP_SYS_ADMIN) || >capable(CAP_DAC_OVERRIDE); > >Can you please reverse the order of the checks? In particular, on an >SELinux based system, a capable() call generates an SELinux denial, >and people often instinctively allow the first operation performed. >Reordering the elements will ensure that the CAP_DAC_OVERRIDE denial >(least permissive) is generated first. Will do in the v2 of every concerned patch. > >> u16 count = same->dest_count; >> struct file *dst_file; >> loff_t dst_off; >> -- >> 2.14.2 >> Nicolas
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