2022-08-23 17:15:06

by Shigeru Yoshida

Subject: [PATCH] fs/ntfs3: Avoid UBSAN error on true_sectors_per_clst()

syzbot reported UBSAN error as below:

[ 76.901829][ T6677] ================================================================================
[ 76.903908][ T6677] UBSAN: shift-out-of-bounds in fs/ntfs3/super.c:675:13
[ 76.905363][ T6677] shift exponent -247 is negative

This patch avoid this error.

Link: https://syzkaller.appspot.com/bug?id=b0299c09a14aababf0f1c862dd4ebc8ab9eb0179
Fixes: a3b774342fa7 (fs/ntfs3: validate BOOT sectors_per_clusters)
Cc: Author: Randy Dunlap <[email protected]>
Reported-by: [email protected]
Signed-off-by: Shigeru Yoshida <[email protected]>
---
fs/ntfs3/super.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ntfs3/super.c b/fs/ntfs3/super.c
index 47012c9bf505..adc4f73722b7 100644
--- a/fs/ntfs3/super.c
+++ b/fs/ntfs3/super.c
@@ -672,7 +672,7 @@ static u32 true_sectors_per_clst(const struct NTFS_BOOT *boot)
if (boot->sectors_per_clusters <= 0x80)
return boot->sectors_per_clusters;
if (boot->sectors_per_clusters >= 0xf4) /* limit shift to 2MB max */
- return 1U << (0 - boot->sectors_per_clusters);
+ return 1U << -(s8)boot->sectors_per_clusters;
return -EINVAL;
}

--
2.37.2

2022-09-07 16:21:34

by Shigeru Yoshida

Subject: Re: [PATCH] fs/ntfs3: Avoid UBSAN error on true_sectors_per_clst()

ping?

On Tue, 23 Aug 2022 23:46:25 +0900, Shigeru Yoshida wrote:
> syzbot reported UBSAN error as below:
>
> [ 76.901829][ T6677] ================================================================================
> [ 76.903908][ T6677] UBSAN: shift-out-of-bounds in fs/ntfs3/super.c:675:13
> [ 76.905363][ T6677] shift exponent -247 is negative
>
> This patch avoid this error.
>
> Link: https://syzkaller.appspot.com/bug?id=b0299c09a14aababf0f1c862dd4ebc8ab9eb0179
> Fixes: a3b774342fa7 (fs/ntfs3: validate BOOT sectors_per_clusters)
> Cc: Author: Randy Dunlap <[email protected]>
> Reported-by: [email protected]
> Signed-off-by: Shigeru Yoshida <[email protected]>
> ---
> fs/ntfs3/super.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/ntfs3/super.c b/fs/ntfs3/super.c
> index 47012c9bf505..adc4f73722b7 100644
> --- a/fs/ntfs3/super.c
> +++ b/fs/ntfs3/super.c
> @@ -672,7 +672,7 @@ static u32 true_sectors_per_clst(const struct NTFS_BOOT *boot)
> if (boot->sectors_per_clusters <= 0x80)
> return boot->sectors_per_clusters;
> if (boot->sectors_per_clusters >= 0xf4) /* limit shift to 2MB max */
> - return 1U << (0 - boot->sectors_per_clusters);
> + return 1U << -(s8)boot->sectors_per_clusters;
> return -EINVAL;
> }
>
> --
> 2.37.2
>

2022-09-30 16:26:34

by Konstantin Komarov

Subject: Re: [PATCH] fs/ntfs3: Avoid UBSAN error on true_sectors_per_clst()

On 8/23/22 17:46, Shigeru Yoshida wrote:
> syzbot reported UBSAN error as below:
>
> [ 76.901829][ T6677] ================================================================================
> [ 76.903908][ T6677] UBSAN: shift-out-of-bounds in fs/ntfs3/super.c:675:13
> [ 76.905363][ T6677] shift exponent -247 is negative
>
> This patch avoid this error.
>
> Link: https://syzkaller.appspot.com/bug?id=b0299c09a14aababf0f1c862dd4ebc8ab9eb0179
> Fixes: a3b774342fa7 (fs/ntfs3: validate BOOT sectors_per_clusters)
> Cc: Author: Randy Dunlap <[email protected]>
> Reported-by: [email protected]
> Signed-off-by: Shigeru Yoshida <[email protected]>
> ---
> fs/ntfs3/super.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/ntfs3/super.c b/fs/ntfs3/super.c
> index 47012c9bf505..adc4f73722b7 100644
> --- a/fs/ntfs3/super.c
> +++ b/fs/ntfs3/super.c
> @@ -672,7 +672,7 @@ static u32 true_sectors_per_clst(const struct NTFS_BOOT *boot)
> if (boot->sectors_per_clusters <= 0x80)
> return boot->sectors_per_clusters;
> if (boot->sectors_per_clusters >= 0xf4) /* limit shift to 2MB max */
> - return 1U << (0 - boot->sectors_per_clusters);
> + return 1U << -(s8)boot->sectors_per_clusters;
> return -EINVAL;
> }
>

Applied, thanks again for the patch!