linux-kernel - [PATCH] generic_permission: MAY

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Message-ID: <20091229205019.GA18257@us.ibm.com>
Date:	Tue, 29 Dec 2009 14:50:19 -0600
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Mike Kazantsev <mk.fraggod@...il.com>,
	Al Viro <viro@....linux.org.uk>
Subject: [PATCH] generic_permission: MAY_OPEN is not write access

generic_permission was refusing CAP_DAC_READ_SEARCH-enabled
processes from opening DAC-protected files read-only, because
do_filp_open adds MAY_OPEN to the open mask.

Ignore MAY_OPEN.  After this patch, CAP_DAC_READ_SEARCH is
again sufficient to open(fname, O_RDONLY) on a file to which
DAC otherwise refuses us read permission.

Reported-by: Mike Kazantsev <mk.fraggod@...il.com>
Signed-off-by: Serge E. Hallyn <serue@...ibm.com>
Tested-by: Mike Kazantsev <mk.fraggod@...il.com>
---
 fs/namei.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 68921d9..b55440b 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -232,6 +232,7 @@ int generic_permission(struct inode *inode, int mask,
 	/*
 	 * Searching includes executable on directories, else just read.
 	 */
+	mask &= MAY_READ | MAY_WRITE | MAY_EXEC;
 	if (mask == MAY_READ || (S_ISDIR(inode->i_mode) && !(mask & MAY_WRITE)))
 		if (capable(CAP_DAC_READ_SEARCH))
 			return 0;
-- 
1.6.0.4

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