[PATCH v2] fs/exfat: resolve memory leak from exfat_create_upcase_table()

[PATCH v2] fs/exfat: resolve memory leak from exfat_create_upcase_table()

[Daniel Yang]

    If exfat_load_upcase_table reaches end and returns -EINVAL,
    allocated memory doesn't get freed and while
    exfat_load_default_upcase_table allocates more memory, leading to a    
    memory leak.
    
    Here's link to syzkaller crash report illustrating this issue:
    https://syzkaller.appspot.com/text?tag=CrashReport&x=1406c201980000

Signed-off-by: Daniel Yang <danielyangkang@gmail.com>
Reported-by: syzbot+e1c69cadec0f1a078e3d@syzkaller.appspotmail.com
---
V1 -> V2: Moved the mem free to create_upcase_table

 fs/exfat/nls.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/exfat/nls.c b/fs/exfat/nls.c
index afdf13c34..8828f9d29 100644
--- a/fs/exfat/nls.c
+++ b/fs/exfat/nls.c
@@ -3,6 +3,7 @@
  * Copyright (C) 2012-2013 Samsung Electronics Co., Ltd.
  */
 
+#include <cerrno>
 #include <linux/string.h>
 #include <linux/slab.h>
 #include <linux/buffer_head.h>
@@ -779,8 +780,13 @@ int exfat_create_upcase_table(struct super_block *sb)
 				le32_to_cpu(ep->dentry.upcase.checksum));
 
 			brelse(bh);
-			if (ret && ret != -EIO)
+			if (ret && ret != -EIO) {
+				/* free memory from exfat_load_upcase_table call */
+				if (ret == -EINVAL) {
+					exfat_free_upcase_table(sbi);
+				}
 				goto load_default;
+			}
 
 			/* load successfully */
 			return ret;
-- 
2.39.2

Re: [PATCH v2] fs/exfat: resolve memory leak from exfat_create_upcase_table()

[Namjae Jeon]

On Mon, Sep 16, 2024 at 2:21 PM Daniel Yang <danielyangkang@gmail.com> wrote:
>
>     If exfat_load_upcase_table reaches end and returns -EINVAL,
>     allocated memory doesn't get freed and while
>     exfat_load_default_upcase_table allocates more memory, leading to a
>     memory leak.
>
>     Here's link to syzkaller crash report illustrating this issue:
>     https://syzkaller.appspot.com/text?tag=CrashReport&x=1406c201980000
>
> Signed-off-by: Daniel Yang <danielyangkang@gmail.com>
> Reported-by: syzbot+e1c69cadec0f1a078e3d@syzkaller.appspotmail.com
> ---
> V1 -> V2: Moved the mem free to create_upcase_table
>
>  fs/exfat/nls.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/fs/exfat/nls.c b/fs/exfat/nls.c
> index afdf13c34..8828f9d29 100644
> --- a/fs/exfat/nls.c
> +++ b/fs/exfat/nls.c
> @@ -3,6 +3,7 @@
>   * Copyright (C) 2012-2013 Samsung Electronics Co., Ltd.
>   */
>
> +#include <cerrno>
Why did you add this?

>  #include <linux/string.h>
>  #include <linux/slab.h>
>  #include <linux/buffer_head.h>
> @@ -779,8 +780,13 @@ int exfat_create_upcase_table(struct super_block *sb)
>                                 le32_to_cpu(ep->dentry.upcase.checksum));
>
>                         brelse(bh);
> -                       if (ret && ret != -EIO)
> +                       if (ret && ret != -EIO) {
> +                               /* free memory from exfat_load_upcase_table call */
> +                               if (ret == -EINVAL) {
Why did you add this check here? If you consider that ->vol_utbl is
NULL, this check is unnecessary.

Thanks.
> +                                       exfat_free_upcase_table(sbi);
> +                               }
>                                 goto load_default;
> +                       }
>
>                         /* load successfully */
>                         return ret;
> --
> 2.39.2
>

Re: [PATCH v2] fs/exfat: resolve memory leak from exfat_create_upcase_table()

[Al Viro]

On Mon, Sep 16, 2024 at 02:58:43PM -0700, Daniel Yang wrote:

> In exfat_create_upcase_table, ENOMEM and EINVAL result in a jump to
> exfat_load_default_upcase_table where memory is also allocated. Since
> ENOMEM doesn't allocate memory, freeing null addresses will result in a
> double free.

Freeing null address is a no-op.  Explicitly guaranteed, for the
same reason why C standard guarantees that free(NULL) is a no-op.
So you don't need to check if allocation had been done.