linux-kernel - Re: lz4: fix system halted at boot kernel x86

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Date:	Wed, 25 Mar 2015 08:04:59 +0100
From:	Krzysztof Kolasa <kkolasa@...soft.pl>
To:	dsterba@...e.cz, tom.yeon@...driver.com,
	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org
Subject: Re: lz4: fix system halted at boot kernel x86_64 compressed lz4

On 25.03.2015 01:44, David Sterba wrote:
> On Tue, Mar 24, 2015 at 12:27:25PM +0100, Krzysztof Kolasa wrote:
>> lz4: fix system halted at boot kernel x86_64 compressed lz4
>>
>> Decompression process ends with an error when loading kernel:
>>
>> Decoding failed
>>  -- System halted
> Serious regression detected ...
>
>> This condition is probably not needed ( from the last commit d5e7caf) :
> The offending patch is on the way to stable trees, so it would be best
> to postpone it for now.
>
>> if( ... ||
>>     (op + COPYLENGTH) > oend)
>>     goto _output_error
>>
>> macro LZ4_SECURE_COPY() tests op and does not copy any data
>> when op exceeds the value, decompression process is continued.
>>
>> added by analogy security for the ref:
>>
>> if ((ref + COPYLENGTH) > oend...
>>
>> to lz4_uncompress_unknownoutputsize(...)
> I did only a quick check, your analysis seems correct. Reviewing the lz4
> patches is tedious as the kernel implementations do not match the
> upstream one line-by-line besides that I've missed the side effects of
> the macro.
>
Add patch source for review (send to LKML) :
---------------------

lz4: fix system halted at boot kernel x86_64 compressed lz4

Decompression process ends with an error when loading kernel:

Decoding failed
 -- System halted

This condition is probably not needed ( from the last commit d5e7caf) :

if( ... ||
    (op + COPYLENGTH) > oend)
    goto _output_error

macro LZ4_SECURE_COPY() tests op and does not copy any data
when op exceeds the value, decompression process is continued.

added by analogy security for the ref:

if ((ref + COPYLENGTH) > oend...

to lz4_uncompress_unknownoutputsize(...)

Signed-off-by: Krzysztof Kolasa <kkolasa@...soft.pl>
---
 lib/lz4/lz4_decompress.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/lib/lz4/lz4_decompress.c b/lib/lz4/lz4_decompress.c
index f0f5c5c..e248c4e 100644
--- a/lib/lz4/lz4_decompress.c
+++ b/lib/lz4/lz4_decompress.c
@@ -139,8 +139,7 @@ static int lz4_uncompress(const char *source, char *dest, int osize)
             /* Error: request to write beyond destination buffer */
             if (cpy > oend)
                 goto _output_error;
-            if ((ref + COPYLENGTH) > oend ||
-                    (op + COPYLENGTH) > oend)
+            if ((ref + COPYLENGTH) > oend)
                 goto _output_error;
             LZ4_SECURECOPY(ref, op, (oend - COPYLENGTH));
             while (op < cpy)
@@ -270,6 +269,8 @@ static int lz4_uncompress_unknownoutputsize(const char *source, char *dest,
         if (cpy > oend - COPYLENGTH) {
             if (cpy > oend)
                 goto _output_error; /* write outside of buf */
+            if ((ref + COPYLENGTH) > oend)
+                goto _output_error;
 
             LZ4_SECURECOPY(ref, op, (oend - COPYLENGTH));
             while (op < cpy)
-- 2.3.3.dirty


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