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[124.171.83.152]) by smtp.gmail.com with ESMTPSA id z11sm162754pfj.104.2020.07.28.16.50.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 28 Jul 2020 16:50:26 -0700 (PDT) Subject: Re: [V9fs-developer] [PATCH kernel] 9p/trans_fd: Check file mode at opening To: Greg Kurz Cc: v9fs-developer@lists.sourceforge.net, Latchesar Ionkov , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Eric Van Hensbergen , Jakub Kicinski , "David S. Miller" , Dominique Martinet References: <20200728124129.130856-1-aik@ozlabs.ru> <20200728194235.52660c08@bahia.lan> From: Alexey Kardashevskiy Autocrypt: addr=aik@ozlabs.ru; keydata= mQINBE+rT0sBEADFEI2UtPRsLLvnRf+tI9nA8T91+jDK3NLkqV+2DKHkTGPP5qzDZpRSH6mD EePO1JqpVuIow/wGud9xaPA5uvuVgRS1q7RU8otD+7VLDFzPRiRE4Jfr2CW89Ox6BF+q5ZPV /pS4v4G9eOrw1v09lEKHB9WtiBVhhxKK1LnUjPEH3ifkOkgW7jFfoYgTdtB3XaXVgYnNPDFo PTBYsJy+wr89XfyHr2Ev7BB3Xaf7qICXdBF8MEVY8t/UFsesg4wFWOuzCfqxFmKEaPDZlTuR tfLAeVpslNfWCi5ybPlowLx6KJqOsI9R2a9o4qRXWGP7IwiMRAC3iiPyk9cknt8ee6EUIxI6 t847eFaVKI/6WcxhszI0R6Cj+N4y+1rHfkGWYWupCiHwj9DjILW9iEAncVgQmkNPpUsZECLT WQzMuVSxjuXW4nJ6f4OFHqL2dU//qR+BM/eJ0TT3OnfLcPqfucGxubhT7n/CXUxEy+mvWwnm s9p4uqVpTfEuzQ0/bE6t7dZdPBua7eYox1AQnk8JQDwC3Rn9kZq2O7u5KuJP5MfludMmQevm pHYEMF4vZuIpWcOrrSctJfIIEyhDoDmR34bCXAZfNJ4p4H6TPqPh671uMQV82CfTxTrMhGFq 8WYU2AH86FrVQfWoH09z1WqhlOm/KZhAV5FndwVjQJs1MRXD8QARAQABtCRBbGV4ZXkgS2Fy ZGFzaGV2c2tpeSA8YWlrQG96bGFicy5ydT6JAjgEEwECACIFAk+rT0sCGwMGCwkIBwMCBhUI 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bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 29/07/2020 03:42, Greg Kurz wrote: > Hi Alexey, > > Working on 9p now ?!? ;-) No, I am running syzkaller and seeing things :) > Cc'ing Dominique Martinet who appears to be the person who takes care of 9p > these days. > > On Tue, 28 Jul 2020 22:41:29 +1000 > Alexey Kardashevskiy wrote: > >> The "fd" transport layer uses 2 file descriptors passed externally >> and calls kernel_write()/kernel_read() on these. If files were opened >> without FMODE_WRITE/FMODE_READ, WARN_ON_ONCE() will fire. >> >> This adds file mode checking in p9_fd_open; this returns -EBADF to >> preserve the original behavior. >> > > So this would cause open() to fail with EBADF, which might look a bit > weird to userspace since it didn't pass an fd... Is this to have a > different error than -EIO that is returned when either rfd or wfd > doesn't point to an open file descriptor ? This is only to preserve the existing behavior. > If yes, why do we care ? Without the patch, p9_fd_open() produces a kernel warning which is not great by itself and becomes crash with panic_on_warn. > >> Found by syzkaller. >> >> Signed-off-by: Alexey Kardashevskiy >> --- >> net/9p/trans_fd.c | 7 ++++++- >> 1 file changed, 6 insertions(+), 1 deletion(-) >> >> diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c >> index 13cd683a658a..62cdfbd01f0a 100644 >> --- a/net/9p/trans_fd.c >> +++ b/net/9p/trans_fd.c >> @@ -797,6 +797,7 @@ static int parse_opts(char *params, struct p9_fd_opts *opts) >> >> static int p9_fd_open(struct p9_client *client, int rfd, int wfd) >> { >> + bool perm; >> struct p9_trans_fd *ts = kzalloc(sizeof(struct p9_trans_fd), >> GFP_KERNEL); >> if (!ts) >> @@ -804,12 +805,16 @@ static int p9_fd_open(struct p9_client *client, int rfd, int wfd) >> >> ts->rd = fget(rfd); >> ts->wr = fget(wfd); >> - if (!ts->rd || !ts->wr) { >> + perm = ts->rd && (ts->rd->f_mode & FMODE_READ) && >> + ts->wr && (ts->wr->f_mode & FMODE_WRITE); >> + if (!ts->rd || !ts->wr || !perm) { >> if (ts->rd) >> fput(ts->rd); >> if (ts->wr) >> fput(ts->wr); >> kfree(ts); >> + if (!perm) >> + return -EBADF; >> return -EIO; >> } >> > -- Alexey