Re: lz4: fix system halted at boot kernel x86_64 compressed lz4

Krzysztof Kolasa
2015-03-25T07:11:19Z

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@winsoft.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