linux-kernel - [PATCH -next] prctl: Fix false positive in validate_prctl

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Message-ID: <20190408143554.GY1421@uranus.lan>
Date:   Mon, 8 Apr 2019 17:35:54 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Andrey Vagin <avagin@...il.com>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Andrew Morton <akpm@...uxfoundation.org>
Subject: [PATCH -next] prctl: Fix false positive in validate_prctl_map

While validating new map we require the @start_data to be strictly less
than @end_data, which is fine for regular applications (this is why this
nit didn't trigger for that long). These members are set from executable
loaders such as elf halders, still it is pretty valid to have a loadable
data section with zero size in file, in such case the start_data is equal
to end_data once kernel loader finishes.

In result when we'are trying to restore such program the procedure fails
and kernel returns -EINVAL. From the image dump of a program:

 | "mm_start_code": "0x400000",
 | "mm_end_code": "0x8f5fb4",
 | "mm_start_data": "0xf1bfb0",
 | "mm_end_data": "0xf1bfb0",

Thus we need to change validate_prctl_map from strictly less to less or
equal operator use.

Fixes: f606b77f1a9e362451aca8f81d8f36a3a112139e
Signed-off-by: Cyrill Gorcunov <gorcunov@...il.com>
CC: Andrey Vagin <avagin@...il.com>
CC: Dmitry Safonov <0x7f454c46@...il.com>
CC: Pavel Emelyanov <xemul@...tuozzo.com>
CC: Andrew Morton <akpm@...uxfoundation.org>
---
I don't consider this issue as a critical one, since it triggered first
time for in more than 4 years period (and report came from a proprietary
program).

 kernel/sys.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-next.git/kernel/sys.c
===================================================================
--- linux-next.git.orig/kernel/sys.c
+++ linux-next.git/kernel/sys.c
@@ -1924,7 +1924,7 @@ static int validate_prctl_map(struct prc
 	((unsigned long)prctl_map->__m1 __op				\
 	 (unsigned long)prctl_map->__m2) ? 0 : -EINVAL
 	error  = __prctl_check_order(start_code, <, end_code);
-	error |= __prctl_check_order(start_data, <, end_data);
+	error |= __prctl_check_order(start_data,<=, end_data);
 	error |= __prctl_check_order(start_brk, <=, brk);
 	error |= __prctl_check_order(arg_start, <=, arg_end);
 	error |= __prctl_check_order(env_start, <=, env_end);