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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id 19sm9669252pfu.85.2021.01.08.11.56.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 08 Jan 2021 11:56:35 -0800 (PST) Date: Fri, 8 Jan 2021 11:56:33 -0800 From: Kees Cook To: Michal Hocko Cc: Xiaoming Ni , linux-kernel@vger.kernel.org, mcgrof@kernel.org, yzaikin@google.com, adobriyan@gmail.com, linux-fsdevel@vger.kernel.org, vbabka@suse.cz, akpm@linux-foundation.org, wangle6@huawei.com Subject: Re: [PATCH v2] proc_sysctl: fix oops caused by incorrect command parameters. Message-ID: <202101081152.0CB22390@keescook> References: <20210108023339.55917-1-nixiaoming@huawei.com> <20210108092145.GX13207@dhcp22.suse.cz> <829bbba0-d3bb-a114-af81-df7390082958@huawei.com> <20210108114718.GA13207@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210108114718.GA13207@dhcp22.suse.cz> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 08, 2021 at 12:47:18PM +0100, Michal Hocko wrote: > On Fri 08-01-21 18:01:52, Xiaoming Ni wrote: > > On 2021/1/8 17:21, Michal Hocko wrote: > > > On Fri 08-01-21 10:33:39, Xiaoming Ni wrote: > > > > The process_sysctl_arg() does not check whether val is empty before > > > > invoking strlen(val). If the command line parameter () is incorrectly > > > > configured and val is empty, oops is triggered. > > > > > > > > For example, "hung_task_panic=1" is incorrectly written as "hung_task_panic". > > > > > > > > log: > > > > Kernel command line: .... hung_task_panic > > > > .... > > > > [000000000000000n] user address but active_mm is swapper > > > > Internal error: Oops: 96000005 [#1] SMP > > > > Modules linked in: > > > > CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.10.1 #1 > > > > Hardware name: linux,dummy-virt (DT) > > > > pstate: 40000005 (nZcv daif -PAN -UAO -TCO BTYPE=--) > > > > pc : __pi_strlen+0x10/0x98 > > > > lr : process_sysctl_arg+0x1e4/0x2ac > > > > sp : ffffffc01104bd40 > > > > x29: ffffffc01104bd40 x28: 0000000000000000 > > > > x27: ffffff80c0a4691e x26: ffffffc0102a7c8c > > > > x25: 0000000000000000 x24: ffffffc01104be80 > > > > x23: ffffff80c22f0b00 x22: ffffff80c02e28c0 > > > > x21: ffffffc0109f9000 x20: 0000000000000000 > > > > x19: ffffffc0107c08de x18: 0000000000000003 > > > > x17: ffffffc01105d000 x16: 0000000000000054 > > > > x15: ffffffffffffffff x14: 3030253078413830 > > > > x13: 000000000000ffff x12: 0000000000000000 > > > > x11: 0101010101010101 x10: 0000000000000005 > > > > x9 : 0000000000000003 x8 : ffffff80c0980c08 > > > > x7 : 0000000000000000 x6 : 0000000000000002 > > > > x5 : ffffff80c0235000 x4 : ffffff810f7c7ee0 > > > > x3 : 000000000000043a x2 : 00bdcc4ebacf1a54 > > > > x1 : 0000000000000000 x0 : 0000000000000000 > > > > Call trace: > > > > __pi_strlen+0x10/0x98 > > > > parse_args+0x278/0x344 > > > > do_sysctl_args+0x8c/0xfc > > > > kernel_init+0x5c/0xf4 > > > > ret_from_fork+0x10/0x30 > > > > Code: b200c3eb 927cec01 f2400c07 54000301 (a8c10c22) > > > > > > > > Fixes: 3db978d480e2843 ("kernel/sysctl: support setting sysctl parameters > > > > from kernel command line") > > > > Signed-off-by: Xiaoming Ni > > > > > > Thanks for catching this! > > > > > > > --------- > > > > v2: > > > > Added log output of the failure branch based on the review comments of Kees Cook. > > > > v1: https://lore.kernel.org/lkml/20201224074256.117413-1-nixiaoming@huawei.com/ > > > > --------- > > > > --- > > > > fs/proc/proc_sysctl.c | 5 +++++ > > > > 1 file changed, 5 insertions(+) > > > > > > > > diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c > > > > index 317899222d7f..dc1a56515e86 100644 > > > > --- a/fs/proc/proc_sysctl.c > > > > +++ b/fs/proc/proc_sysctl.c > > > > @@ -1757,6 +1757,11 @@ static int process_sysctl_arg(char *param, char *val, > > > > loff_t pos = 0; > > > > ssize_t wret; > > > > + if (!val) { > > > > + pr_err("Missing param value! Expected '%s=...value...'\n", param); > > > > + return 0; > > I may need to move the validation code for val to the end of the validation > > code for param to prevent non-sysctl arguments from triggering the current > > print. > > Why would that matter? A missing value is clearly a error path and it > should be reported. This test is in the correct place. I think it's just a question of the return values. > > Or delete the print and keep it silent for a little better performance. > > Which is better? > > I do not think there is a performance argument on the table. The generic > code is returning EINVAL on a missing value where it is needed. Sysctl > all require a value IIRC so EINVAL would be the right way to report > this and let the generic code to complain. The reason the others do a "return 0" is because other error conditions will end up double-reporting: switch (ret) { case 0: continue; case -ENOENT: pr_err("%s: Unknown parameter `%s'\n", doing, param); break; case -ENOSPC: pr_err("%s: `%s' too large for parameter `%s'\n", doing, val ?: "", param); break; default: pr_err("%s: `%s' invalid for parameter `%s'\n", doing, val ?: "", param); break; } Also note that where the sysctl parsing happens, it calls parse_args() without checking return codes, so that doesn't matter either. It's possible that doing this would be sufficient, though: + if (!val) + return -EINVAL; Since that would hit the "default" error report which looks reasonable. -- Kees Cook