2021-06-05 05:14:24

by Ritesh Harjani

[permalink] [raw]
Subject: [PATCH] ext4: Fix loff_t overflow in ext4_max_bitmap_size()

We should use unsigned long long rather than loff_t to avoid
overflow in ext4_max_bitmap_size() for comparison before returning.
w/o this patch sbi->s_bitmap_maxbytes was becoming a negative
value due to overflow of upper_limit (with has_huge_files as true)

Below is a quick test to trigger it on a 64KB pagesize system.

sudo mkfs.ext4 -b 65536 -O ^has_extents,^64bit /dev/loop2
sudo mount /dev/loop2 /mnt
sudo echo "hello" > /mnt/hello -> This will error out with
"echo: write error: File too large"

Signed-off-by: Ritesh Harjani <[email protected]>
---
fs/ext4/super.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 7dc94f3e18e6..bedb66386966 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3189,17 +3189,17 @@ static loff_t ext4_max_size(int blkbits, int has_huge_files)
*/
static loff_t ext4_max_bitmap_size(int bits, int has_huge_files)
{
- loff_t res = EXT4_NDIR_BLOCKS;
+ unsigned long long upper_limit, res = EXT4_NDIR_BLOCKS;
int meta_blocks;
- loff_t upper_limit;
- /* This is calculated to be the largest file size for a dense, block
+
+ /*
+ * This is calculated to be the largest file size for a dense, block
* mapped file such that the file's total number of 512-byte sectors,
* including data and all indirect blocks, does not exceed (2^48 - 1).
*
* __u32 i_blocks_lo and _u16 i_blocks_high represent the total
* number of 512-byte sectors of the file.
*/
-
if (!has_huge_files) {
/*
* !has_huge_files or implies that the inode i_block field
@@ -3242,7 +3242,7 @@ static loff_t ext4_max_bitmap_size(int bits, int has_huge_files)
if (res > MAX_LFS_FILESIZE)
res = MAX_LFS_FILESIZE;

- return res;
+ return (loff_t)res;
}

static ext4_fsblk_t descriptor_loc(struct super_block *sb,
--
2.31.1


2021-06-07 10:01:09

by Jan Kara

[permalink] [raw]
Subject: Re: [PATCH] ext4: Fix loff_t overflow in ext4_max_bitmap_size()

On Sat 05-06-21 10:39:32, Ritesh Harjani wrote:
> We should use unsigned long long rather than loff_t to avoid
> overflow in ext4_max_bitmap_size() for comparison before returning.
> w/o this patch sbi->s_bitmap_maxbytes was becoming a negative
> value due to overflow of upper_limit (with has_huge_files as true)
>
> Below is a quick test to trigger it on a 64KB pagesize system.
>
> sudo mkfs.ext4 -b 65536 -O ^has_extents,^64bit /dev/loop2
> sudo mount /dev/loop2 /mnt
> sudo echo "hello" > /mnt/hello -> This will error out with
> "echo: write error: File too large"
>
> Signed-off-by: Ritesh Harjani <[email protected]>

OK, this works (although it's really tight ;). Won't it be somewhat safer
if we compared upper_limit and res before shifting both by blocksize_bits
to the left? Basically we need to shift only for comparison with
MAX_LFS_FILESIZE which is in bytes... But either way feel free to add:

Reviewed-by: Jan Kara <[email protected]>

Honza

> ---
> fs/ext4/super.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 7dc94f3e18e6..bedb66386966 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -3189,17 +3189,17 @@ static loff_t ext4_max_size(int blkbits, int has_huge_files)
> */
> static loff_t ext4_max_bitmap_size(int bits, int has_huge_files)
> {
> - loff_t res = EXT4_NDIR_BLOCKS;
> + unsigned long long upper_limit, res = EXT4_NDIR_BLOCKS;
> int meta_blocks;
> - loff_t upper_limit;
> - /* This is calculated to be the largest file size for a dense, block
> +
> + /*
> + * This is calculated to be the largest file size for a dense, block
> * mapped file such that the file's total number of 512-byte sectors,
> * including data and all indirect blocks, does not exceed (2^48 - 1).
> *
> * __u32 i_blocks_lo and _u16 i_blocks_high represent the total
> * number of 512-byte sectors of the file.
> */
> -
> if (!has_huge_files) {
> /*
> * !has_huge_files or implies that the inode i_block field
> @@ -3242,7 +3242,7 @@ static loff_t ext4_max_bitmap_size(int bits, int has_huge_files)
> if (res > MAX_LFS_FILESIZE)
> res = MAX_LFS_FILESIZE;
>
> - return res;
> + return (loff_t)res;
> }
>
> static ext4_fsblk_t descriptor_loc(struct super_block *sb,
> --
> 2.31.1
>
--
Jan Kara <[email protected]>
SUSE Labs, CR

2021-06-19 08:57:21

by Ritesh Harjani

[permalink] [raw]
Subject: Re: [PATCH] ext4: Fix loff_t overflow in ext4_max_bitmap_size()

On 21/06/07 12:00PM, Jan Kara wrote:
> On Sat 05-06-21 10:39:32, Ritesh Harjani wrote:
> > We should use unsigned long long rather than loff_t to avoid
> > overflow in ext4_max_bitmap_size() for comparison before returning.
> > w/o this patch sbi->s_bitmap_maxbytes was becoming a negative
> > value due to overflow of upper_limit (with has_huge_files as true)
> >
> > Below is a quick test to trigger it on a 64KB pagesize system.
> >
> > sudo mkfs.ext4 -b 65536 -O ^has_extents,^64bit /dev/loop2
> > sudo mount /dev/loop2 /mnt
> > sudo echo "hello" > /mnt/hello -> This will error out with
> > "echo: write error: File too large"
> >
> > Signed-off-by: Ritesh Harjani <[email protected]>
>
> OK, this works (although it's really tight ;). Won't it be somewhat safer
> if we compared upper_limit and res before shifting both by blocksize_bits
> to the left? Basically we need to shift only for comparison with
> MAX_LFS_FILESIZE which is in bytes... But either way feel free to add:

Yes, at 1st I did think that, but since for comparing "res" against
MAX_LFS_FILESIZE we will be anyway doing the bit shifting and since this logic
too was (just) fitting into the limits so I thought of keeping it the same.
But, if absolutely required, I can make those changes.

>
> Reviewed-by: Jan Kara <[email protected]>


Thanks for the review :)

-ritesh

>
> Honza
>
> > ---
> > fs/ext4/super.c | 10 +++++-----
> > 1 file changed, 5 insertions(+), 5 deletions(-)
> >
> > diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> > index 7dc94f3e18e6..bedb66386966 100644
> > --- a/fs/ext4/super.c
> > +++ b/fs/ext4/super.c
> > @@ -3189,17 +3189,17 @@ static loff_t ext4_max_size(int blkbits, int has_huge_files)
> > */
> > static loff_t ext4_max_bitmap_size(int bits, int has_huge_files)
> > {
> > - loff_t res = EXT4_NDIR_BLOCKS;
> > + unsigned long long upper_limit, res = EXT4_NDIR_BLOCKS;
> > int meta_blocks;
> > - loff_t upper_limit;
> > - /* This is calculated to be the largest file size for a dense, block
> > +
> > + /*
> > + * This is calculated to be the largest file size for a dense, block
> > * mapped file such that the file's total number of 512-byte sectors,
> > * including data and all indirect blocks, does not exceed (2^48 - 1).
> > *
> > * __u32 i_blocks_lo and _u16 i_blocks_high represent the total
> > * number of 512-byte sectors of the file.
> > */
> > -
> > if (!has_huge_files) {
> > /*
> > * !has_huge_files or implies that the inode i_block field
> > @@ -3242,7 +3242,7 @@ static loff_t ext4_max_bitmap_size(int bits, int has_huge_files)
> > if (res > MAX_LFS_FILESIZE)
> > res = MAX_LFS_FILESIZE;
> >
> > - return res;
> > + return (loff_t)res;
> > }
> >
> > static ext4_fsblk_t descriptor_loc(struct super_block *sb,
> > --
> > 2.31.1
> >
> --
> Jan Kara <[email protected]>
> SUSE Labs, CR