linux-kernel - [PATCH] fs: Use CAP_DAC_OVERRIDE to allow for file dedupe

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Message-Id: <20171021132806.18086-1-nicolas@belouin.fr>
Date:   Sat, 21 Oct 2017 15:28:06 +0200
From:   Nicolas Belouin <nicolas@...ouin.fr>
To:     Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-api@...r.kernel.org, kernel-hardening@...ts.openwall.com
Cc:     Nicolas Belouin <nicolas@...ouin.fr>
Subject: [PATCH] fs: Use CAP_DAC_OVERRIDE to allow for file dedupe

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);
 	u16 count = same->dest_count;
 	struct file *dst_file;
 	loff_t dst_off;
-- 
2.14.2