[PATCH] module: Fix NULL vs IS_ERR checking for module_get_next_page

The module_get_next_page() function return error pointers on error
instead of NULL.
Use IS_ERR() to check the return value to fix this.

Fixes: b1ae6dc41eaa ("module: add in-kernel support for decompressing")
Signed-off-by: Miaoqian Lin <redacted>
---
 kernel/module/decompress.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/module/decompress.c b/kernel/module/decompress.c
index c033572d83f0..720e719253cd 100644
--- a/kernel/module/decompress.c
+++ b/kernel/module/decompress.c

@@ -114,8 +114,8 @@ static ssize_t module_gzip_decompress(struct load_info *info,
 	do {
 		struct page *page = module_get_next_page(info);
 
-		if (!page) {
-			retval = -ENOMEM;
+		if (IS_ERR(page)) {
+			retval = PTR_ERR(page);
 			goto out_inflate_end;
 		}
 

@@ -173,8 +173,8 @@ static ssize_t module_xz_decompress(struct load_info *info,
 	do {
 		struct page *page = module_get_next_page(info);
 
-		if (!page) {
-			retval = -ENOMEM;
+		if (IS_ERR(page)) {
+			retval = PTR_ERR(page);
 			goto out;
 		}
 

-- 
2.37.3.671.ge2130fe6da78.dirty

On Thu, Nov 10, 2022 at 06:58:34AM +0400, Miaoqian Lin wrote:

The module_get_next_page() function return error pointers on error
instead of NULL.
Use IS_ERR() to check the return value to fix this.

Fixes: b1ae6dc41eaa ("module: add in-kernel support for decompressing")
Signed-off-by: Miaoqian Lin <redacted>
---

Thanks queued up. How did you find out? Just code inspection? I see
chances are low of this triggering, but just curious how you found it.

  Luis

Hi,

On 2022/11/10 12:09, Luis Chamberlain wrote:

On Thu, Nov 10, 2022 at 06:58:34AM +0400, Miaoqian Lin wrote:

quoted

The module_get_next_page() function return error pointers on error
instead of NULL.
Use IS_ERR() to check the return value to fix this.

Fixes: b1ae6dc41eaa ("module: add in-kernel support for decompressing")
Signed-off-by: Miaoqian Lin <redacted>
---

Thanks queued up. How did you find out? Just code inspection? I see
chances are low of this triggering, but just curious how you found it.

I found this by static analysis, specifically, I obtained functions that return error pointers and

inspected whether their callers followed the correct specification.

  Luis

On Thu, Nov 10, 2022 at 12:18:50PM +0800, Miaoqian Lin wrote:

Hi,

On 2022/11/10 12:09, Luis Chamberlain wrote:

quoted

On Thu, Nov 10, 2022 at 06:58:34AM +0400, Miaoqian Lin wrote:

quoted

The module_get_next_page() function return error pointers on error
instead of NULL.
Use IS_ERR() to check the return value to fix this.

Fixes: b1ae6dc41eaa ("module: add in-kernel support for decompressing")
Signed-off-by: Miaoqian Lin <redacted>
---

Thanks queued up. How did you find out? Just code inspection? I see
chances are low of this triggering, but just curious how you found it.

I found this by static analysis, specifically, I obtained functions that return error pointers and
inspected whether their callers followed the correct specification.

Which one did you use?

  Luis

On 2022/11/10 14:05, Luis Chamberlain wrote:

On Thu, Nov 10, 2022 at 12:18:50PM +0800, Miaoqian Lin wrote:

quoted

Hi,

On 2022/11/10 12:09, Luis Chamberlain wrote:

quoted

On Thu, Nov 10, 2022 at 06:58:34AM +0400, Miaoqian Lin wrote:

quoted

The module_get_next_page() function return error pointers on error
instead of NULL.
Use IS_ERR() to check the return value to fix this.

Fixes: b1ae6dc41eaa ("module: add in-kernel support for decompressing")
Signed-off-by: Miaoqian Lin <redacted>
---

Thanks queued up. How did you find out? Just code inspection? I see
chances are low of this triggering, but just curious how you found it.

I found this by static analysis, specifically, I obtained functions that return error pointers and
inspected whether their callers followed the correct specification.

Which one did you use?

I wrote custom checker based on the weggli tool (https://github.com/googleprojectzero/weggli).

  Luis

On Thu, Nov 10, 2022 at 06:58:34AM +0400, Miaoqian Lin wrote:

The module_get_next_page() function return error pointers on error
instead of NULL.
Use IS_ERR() to check the return value to fix this.

Fixes: b1ae6dc41eaa ("module: add in-kernel support for decompressing")
Signed-off-by: Miaoqian Lin <redacted>

Reviewed-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Thank you for spotting this.

-- 
Dmitry