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Bruce Fields" , Alexander Viro , linux-fsdevel@vger.kernel.org, Jeff Layton Subject: [PATCH 4.4 45/74] fs/fcntl: f_setown, avoid undefined behaviour Date: Mon, 29 Jan 2018 13:56:50 +0100 Message-Id: <20180129123849.600818453@linuxfoundation.org> X-Mailer: git-send-email 2.16.1 In-Reply-To: <20180129123847.507563674@linuxfoundation.org> References: <20180129123847.507563674@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jiri Slaby commit fc3dc67471461c0efcb1ed22fb7595121d65fad9 upstream. fcntl(0, F_SETOWN, 0x80000000) triggers: UBSAN: Undefined behaviour in fs/fcntl.c:118:7 negation of -2147483648 cannot be represented in type 'int': CPU: 1 PID: 18261 Comm: syz-executor Not tainted 4.8.1-0-syzkaller #1 ... Call Trace: ... [] ? f_setown+0x1d8/0x200 [] ? SyS_fcntl+0x999/0xf30 [] ? entry_SYSCALL_64_fastpath+0x23/0xc1 Fix that by checking the arg parameter properly (against INT_MAX) before "who = -who". And return immediatelly with -EINVAL in case it is wrong. Note that according to POSIX we can return EINVAL: http://pubs.opengroup.org/onlinepubs/9699919799/functions/fcntl.html [EINVAL] The cmd argument is F_SETOWN and the value of the argument is not valid as a process or process group identifier. [v2] returns an error, v1 used to fail silently [v3] implement proper check for the bad value INT_MIN Signed-off-by: Jiri Slaby Cc: Jeff Layton Cc: "J. Bruce Fields" Cc: Alexander Viro Cc: linux-fsdevel@vger.kernel.org Signed-off-by: Jeff Layton Signed-off-by: Greg Kroah-Hartman --- fs/fcntl.c | 4 ++++ 1 file changed, 4 insertions(+) --- a/fs/fcntl.c +++ b/fs/fcntl.c @@ -113,6 +113,10 @@ void f_setown(struct file *filp, unsigne int who = arg; type = PIDTYPE_PID; if (who < 0) { + /* avoid overflow below */ + if (who == INT_MIN) + return; + type = PIDTYPE_PGID; who = -who; }