[PATCH 4.2] zram: fix pool names truncation

[PATCH 4.2] zram: fix pool names truncation

[Sergey Senozhatsky]

Hello,

found this reading the code just now. I do believe we need this
patch in 4.2 (before 4.3), because the bug breaks new devices
creation under some specific conditions -- new pool names are
getting truncated to only 3 digits and, thus,
debugfs_create_dir() fails.

The commit message contains more details.


Andrew, can you please pick up this patch?


Sergey Senozhatsky (1):
  zram: fix max pool limitation

 drivers/block/zram/zram_drv.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

-- 
2.5.0

[PATCH] zram: fix max pool limitation

[Sergey Senozhatsky]

zram_meta_alloc() constructs a pool name for zs_create_pool() call
as
 snprintf(pool_name, sizeof(pool_name), "zram%d", device_id);

However, it defines pool name buffer to be only 8 chars long
(minus trailing zero), which means that we can have only 1000
pool names: zram0 -- zram999.

With CONFIG_ZSMALLOC_STAT enabled an attempt to create a device
zram1000 can fail if device zram100 already exists, because
snprintf() will truncate new pool name to zram100 and pass it
to debugfs_create_dir(), causing:

  debugfs dir <zram100> creation failed
  zram: Error creating memory pool

... and so on (zram101 - zram1010, etc).

Fix it by increasing pool_name buffer size to 11:
-- zram prefix (length 4)
-- int device_id can use up to 10 chars
-- terminating zero byte

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
---
 drivers/block/zram/zram_drv.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index b088ca9..1dec01d 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -502,7 +502,7 @@ static void zram_meta_free(struct zram_meta *meta, u64 disksize)
 static struct zram_meta *zram_meta_alloc(int device_id, u64 disksize)
 {
 	size_t num_pages;
-	char pool_name[8];
+	char pool_name[15];
 	struct zram_meta *meta = kmalloc(sizeof(*meta), GFP_KERNEL);
 
 	if (!meta)
-- 
2.5.0

Re: [PATCH] zram: fix max pool limitation

[Sergey Senozhatsky]

On (08/11/15 22:33), Sergey Senozhatsky wrote:
> zram_meta_alloc() constructs a pool name for zs_create_pool() call
> as
>  snprintf(pool_name, sizeof(pool_name), "zram%d", device_id);
> 
> However, it defines pool name buffer to be only 8 chars long
> (minus trailing zero), which means that we can have only 1000
> pool names: zram0 -- zram999.
> 
> With CONFIG_ZSMALLOC_STAT enabled an attempt to create a device
> zram1000 can fail if device zram100 already exists, because
> snprintf() will truncate new pool name to zram100 and pass it
> to debugfs_create_dir(), causing:
> 
>   debugfs dir <zram100> creation failed
>   zram: Error creating memory pool
> 
> ... and so on (zram101 - zram1010, etc).
> 
> Fix it by increasing pool_name buffer size to 11:

oh... don't know how this happened. to 15.

	-ss

> -- zram prefix (length 4)
> -- int device_id can use up to 10 chars
> -- terminating zero byte
> 
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> ---
>  drivers/block/zram/zram_drv.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index b088ca9..1dec01d 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -502,7 +502,7 @@ static void zram_meta_free(struct zram_meta *meta, u64 disksize)
>  static struct zram_meta *zram_meta_alloc(int device_id, u64 disksize)
>  {
>  	size_t num_pages;
> -	char pool_name[8];
> +	char pool_name[15];
>  	struct zram_meta *meta = kmalloc(sizeof(*meta), GFP_KERNEL);
>  
>  	if (!meta)
> -- 
> 2.5.0
> 

[PATCH v2] zram: fix pool name truncation

[Sergey Senozhatsky]

zram_meta_alloc() constructs a pool name for zs_create_pool() call
as
 snprintf(pool_name, sizeof(pool_name), "zram%d", device_id);

However, it defines pool name buffer to be only 8 chars long
(minus trailing zero), which means that we can have only 1000
pool names: zram0 -- zram999.

With CONFIG_ZSMALLOC_STAT enabled an attempt to create a device
zram1000 can fail if device zram100 already exists, because
snprintf() will truncate new pool name to zram100 and pass it
to debugfs_create_dir(), causing:

  debugfs dir <zram100> creation failed
  zram: Error creating memory pool

... and so on (zram101 - zram1010, etc).

Fix it by increasing pool_name buffer size to 15:
-- zram prefix (length 4)
-- int device_id can use up to 10 chars
-- terminating zero byte

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
---
 drivers/block/zram/zram_drv.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index b088ca9..1dec01d 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -502,7 +502,7 @@ static void zram_meta_free(struct zram_meta *meta, u64 disksize)
 static struct zram_meta *zram_meta_alloc(int device_id, u64 disksize)
 {
 	size_t num_pages;
-	char pool_name[8];
+	char pool_name[15];
 	struct zram_meta *meta = kmalloc(sizeof(*meta), GFP_KERNEL);
 
 	if (!meta)
-- 
2.5.0

Re: [PATCH 4.2] zram: fix pool names truncation

[Sergey Senozhatsky]

On (08/11/15 22:33), Sergey Senozhatsky wrote:
> found this reading the code just now. I do believe we need this
> patch in 4.2 (before 4.3), because the bug breaks new devices
> creation under some specific conditions -- new pool names are
> getting truncated to only 3 digits and, thus,
> debugfs_create_dir() fails.
> 
> The commit message contains more details.
> 

Hello,

I have an alternative fix; a somewhat better one. We actually
don't have to snprintf() there anything. We already have
zram->disk->disk_name constructed exactly same way, so we can
pass it to zram_meta_alloc() instead of device_id.

I'll send out a patch shortly.

	-ss

> 
> Andrew, can you please pick up this patch?
> 
> 
> Sergey Senozhatsky (1):
>   zram: fix max pool limitation
> 
>  drivers/block/zram/zram_drv.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> -- 
> 2.5.0
> 

[PATCH v3] zram: fix pool name truncation

[Sergey Senozhatsky]

zram_meta_alloc() constructs a pool name for zs_create_pool() call
as
 snprintf(pool_name, sizeof(pool_name), "zram%d", device_id);

However, it defines pool name buffer to be only 8 bytes long
(minus trailing zero), which means that we can have only 1000
pool names: zram0 -- zram999.

With CONFIG_ZSMALLOC_STAT enabled an attempt to create a device
zram1000 can fail if device zram100 already exists, because
snprintf() will truncate new pool name to zram100 and pass it
debugfs_create_dir(), causing:

  debugfs dir <zram100> creation failed
  zram: Error creating memory pool

... and so on.

Fix it by passing zram->disk->disk_name to zram_meta_alloc()
instead of divice_id. We construct zram%d name earlier and
keep it as a ->disk_name, no need to snprintf() it again.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
---
 drivers/block/zram/zram_drv.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index b088ca9..c87d2f6 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -499,10 +499,9 @@ static void zram_meta_free(struct zram_meta *meta, u64 disksize)
 	kfree(meta);
 }
 
-static struct zram_meta *zram_meta_alloc(int device_id, u64 disksize)
+static struct zram_meta *zram_meta_alloc(char *pool_name, u64 disksize)
 {
 	size_t num_pages;
-	char pool_name[8];
 	struct zram_meta *meta = kmalloc(sizeof(*meta), GFP_KERNEL);
 
 	if (!meta)
@@ -515,7 +514,6 @@ static struct zram_meta *zram_meta_alloc(int device_id, u64 disksize)
 		goto out_error;
 	}
 
-	snprintf(pool_name, sizeof(pool_name), "zram%d", device_id);
 	meta->mem_pool = zs_create_pool(pool_name, GFP_NOIO | __GFP_HIGHMEM);
 	if (!meta->mem_pool) {
 		pr_err("Error creating memory pool\n");
@@ -1033,7 +1031,7 @@ static ssize_t disksize_store(struct device *dev,
 		return -EINVAL;
 
 	disksize = PAGE_ALIGN(disksize);
-	meta = zram_meta_alloc(zram->disk->first_minor, disksize);
+	meta = zram_meta_alloc(zram->disk->disk_name, disksize);
 	if (!meta)
 		return -ENOMEM;
 
-- 
2.5.0