[PATCH][RESEND] staging: zram: fix invalid memory references during disk write

[PATCH][RESEND] staging: zram: fix invalid memory references during disk write

[Nitin Gupta]

Fixes a bug introduced by commit c8f2f0db1 ("zram: Fix handling
of incompressible pages") which caused invalid memory references
during disk write. Invalid references could occur in two cases:
 - Incoming data expands on compression: In this case, reference was
made to kunmap()'ed bio page.
 - Partial (non PAGE_SIZE) write with incompressible data: In this
case, reference was made to a kfree()'ed buffer.

Fixes bug 50081:
https://bugzilla.kernel.org/show_bug.cgi?id=50081

Signed-off-by: Nitin Gupta <ngupta@vflare.org>
Reported-by: Mihail Kasadjikov <hamer.mk@gmail.com>
Reported-by: Tomas M <tomas@slax.org>
Reviewed-by: Minchan Kim <minchan@kernel.org>
---
 drivers/staging/zram/zram_drv.c |   39 ++++++++++++++++++++++++---------------
 1 file changed, 24 insertions(+), 15 deletions(-)

diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
index fb4a7c9..f2a73bd 100644
--- a/drivers/staging/zram/zram_drv.c
+++ b/drivers/staging/zram/zram_drv.c
@@ -265,7 +265,7 @@ out_cleanup:
 static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 			   int offset)
 {
-	int ret;
+	int ret = 0;
 	size_t clen;
 	unsigned long handle;
 	struct page *page;
@@ -286,10 +286,8 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 			goto out;
 		}
 		ret = zram_decompress_page(zram, uncmem, index);
-		if (ret) {
-			kfree(uncmem);
+		if (ret)
 			goto out;
-		}
 	}
 
 	/*
@@ -302,16 +300,18 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 
 	user_mem = kmap_atomic(page);
 
-	if (is_partial_io(bvec))
+	if (is_partial_io(bvec)) {
 		memcpy(uncmem + offset, user_mem + bvec->bv_offset,
 		       bvec->bv_len);
-	else
+		kunmap_atomic(user_mem);
+		user_mem = NULL;
+	} else {
 		uncmem = user_mem;
+	}
 
 	if (page_zero_filled(uncmem)) {
-		kunmap_atomic(user_mem);
-		if (is_partial_io(bvec))
-			kfree(uncmem);
+		if (!is_partial_io(bvec))
+			kunmap_atomic(user_mem);
 		zram_stat_inc(&zram->stats.pages_zero);
 		zram_set_flag(zram, index, ZRAM_ZERO);
 		ret = 0;
@@ -321,9 +321,11 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 	ret = lzo1x_1_compress(uncmem, PAGE_SIZE, src, &clen,
 			       zram->compress_workmem);
 
-	kunmap_atomic(user_mem);
-	if (is_partial_io(bvec))
-			kfree(uncmem);
+	if (!is_partial_io(bvec)) {
+		kunmap_atomic(user_mem);
+		user_mem = NULL;
+		uncmem = NULL;
+	}
 
 	if (unlikely(ret != LZO_E_OK)) {
 		pr_err("Compression failed! err=%d\n", ret);
@@ -332,8 +334,10 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 
 	if (unlikely(clen > max_zpage_size)) {
 		zram_stat_inc(&zram->stats.bad_compress);
-		src = uncmem;
 		clen = PAGE_SIZE;
+		src = NULL;
+		if (is_partial_io(bvec))
+			src = uncmem;
 	}
 
 	handle = zs_malloc(zram->mem_pool, clen);
@@ -345,7 +349,11 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 	}
 	cmem = zs_map_object(zram->mem_pool, handle, ZS_MM_WO);
 
+	if ((clen == PAGE_SIZE) && !is_partial_io(bvec))
+		src = kmap_atomic(page);
 	memcpy(cmem, src, clen);
+	if ((clen == PAGE_SIZE) && !is_partial_io(bvec))
+		kunmap_atomic(src);
 
 	zs_unmap_object(zram->mem_pool, handle);
 
@@ -358,9 +366,10 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 	if (clen <= PAGE_SIZE / 2)
 		zram_stat_inc(&zram->stats.good_compress);
 
-	return 0;
-
 out:
+	if (is_partial_io(bvec))
+		kfree(uncmem);
+
 	if (ret)
 		zram_stat64_inc(zram, &zram->stats.failed_writes);
 	return ret;
-- 
1.7.10.4

Re: [PATCH][RESEND] staging: zram: fix invalid memory references during disk write

[Nitin Gupta]

On Wed, Jan 2, 2013 at 8:53 AM, Nitin Gupta <ngupta@vflare.org> wrote:
> Fixes a bug introduced by commit c8f2f0db1 ("zram: Fix handling
> of incompressible pages") which caused invalid memory references
> during disk write. Invalid references could occur in two cases:
>  - Incoming data expands on compression: In this case, reference was
> made to kunmap()'ed bio page.
>  - Partial (non PAGE_SIZE) write with incompressible data: In this
> case, reference was made to a kfree()'ed buffer.
>
> Fixes bug 50081:
> https://bugzilla.kernel.org/show_bug.cgi?id=50081
>

Greg: can you please add this to staging? It fixes an important issue
and is tested by many users.

Nitin

Re: [PATCH][RESEND] staging: zram: fix invalid memory references during disk write

[Nitin Gupta]

On Fri, Jan 4, 2013 at 12:25 PM, Nitin Gupta <ngupta@vflare.org> wrote:
> On Wed, Jan 2, 2013 at 8:53 AM, Nitin Gupta <ngupta@vflare.org> wrote:
>> Fixes a bug introduced by commit c8f2f0db1 ("zram: Fix handling
>> of incompressible pages") which caused invalid memory references
>> during disk write. Invalid references could occur in two cases:
>>  - Incoming data expands on compression: In this case, reference was
>> made to kunmap()'ed bio page.
>>  - Partial (non PAGE_SIZE) write with incompressible data: In this
>> case, reference was made to a kfree()'ed buffer.
>>
>> Fixes bug 50081:
>> https://bugzilla.kernel.org/show_bug.cgi?id=50081
>>
>
> Greg: can you please add this to staging? It fixes an important issue
> and is tested by many users.
>


It's still not in staging. Any reason why you want to accept this patch?
Of course, this is the last reminder, won't bother you again.

Thanks,
Nitin

Re: [PATCH][RESEND] staging: zram: fix invalid memory references during disk write

[Greg KH]

On Tue, Jan 08, 2013 at 02:00:27PM -0800, Nitin Gupta wrote:
> On Fri, Jan 4, 2013 at 12:25 PM, Nitin Gupta <ngupta@vflare.org> wrote:
> > On Wed, Jan 2, 2013 at 8:53 AM, Nitin Gupta <ngupta@vflare.org> wrote:
> >> Fixes a bug introduced by commit c8f2f0db1 ("zram: Fix handling
> >> of incompressible pages") which caused invalid memory references
> >> during disk write. Invalid references could occur in two cases:
> >>  - Incoming data expands on compression: In this case, reference was
> >> made to kunmap()'ed bio page.
> >>  - Partial (non PAGE_SIZE) write with incompressible data: In this
> >> case, reference was made to a kfree()'ed buffer.
> >>
> >> Fixes bug 50081:
> >> https://bugzilla.kernel.org/show_bug.cgi?id=50081
> >>
> >
> > Greg: can you please add this to staging? It fixes an important issue
> > and is tested by many users.
> >
> 
> 
> It's still not in staging. Any reason why you want to accept this patch?

Because I'm still catching up after being on vacation for 3 weeks?  I
only got back yesterday and have a few thousand emails/patches to make
it through.  Patches for staging drivers are way down on the list of
priorities for me, especially the zram/zcache/zwhatever mess that we
currently have...

Don't worry, it's not lost, and will make it in soon, please give me a
chance.

greg k-h