linux-kernel - [PATCH 3.11 13/36] ipc,shm: correct error return value in shmctl (SHM

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Message-Id: <20131126181027.767956290@linuxfoundation.org>
Date:	Tue, 26 Nov 2013 10:12:23 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Jesper Nilsson <jesper.nilsson@...s.com>,
	Davidlohr Bueso <davidlohr@...com>,
	Rik van Riel <riel@...hat.com>,
	Michel Lespinasse <walken@...gle.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 3.11 13/36] ipc,shm: correct error return value in shmctl (SHM_UNLOCK)

3.11-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jesper Nilsson <jesper.nilsson@...s.com>

commit 3a72660b07d86d60457ca32080b1ce8c2b628ee2 upstream.

Commit 2caacaa82a51 ("ipc,shm: shorten critical region for shmctl")
restructured the ipc shm to shorten critical region, but introduced a
path where the return value could be -EPERM, even if the operation
actually was performed.

Before the commit, the err return value was reset by the return value
from security_shm_shmctl() after the if (!ns_capable(...)) statement.

Now, we still exit the if statement with err set to -EPERM, and in the
case of SHM_UNLOCK, it is not reset at all, and used as the return value
from shmctl.

To fix this, we only set err when errors occur, leaving the fallthrough
case alone.

Signed-off-by: Jesper Nilsson <jesper.nilsson@...s.com>
Cc: Davidlohr Bueso <davidlohr@...com>
Cc: Rik van Riel <riel@...hat.com>
Cc: Michel Lespinasse <walken@...gle.com>
Cc: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 ipc/shm.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -974,12 +974,15 @@ SYSCALL_DEFINE3(shmctl, int, shmid, int,
 		ipc_lock_object(&shp->shm_perm);
 		if (!ns_capable(ns->user_ns, CAP_IPC_LOCK)) {
 			kuid_t euid = current_euid();
-			err = -EPERM;
 			if (!uid_eq(euid, shp->shm_perm.uid) &&
-			    !uid_eq(euid, shp->shm_perm.cuid))
+			    !uid_eq(euid, shp->shm_perm.cuid)) {
+				err = -EPERM;
 				goto out_unlock0;
-			if (cmd == SHM_LOCK && !rlimit(RLIMIT_MEMLOCK))
+			}
+			if (cmd == SHM_LOCK && !rlimit(RLIMIT_MEMLOCK)) {
+				err = -EPERM;
 				goto out_unlock0;
+			}
 		}
 
 		shm_file = shp->shm_file;


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