Syzbot found an issue [1] in ext4_fallocate().
The C reproducer [2] calls fallocate(), passing size 0xffeffeff000ul,
and offset 0x1000000ul, which, when added together exceed the disk size,
and trigger a BUG in ext4_ind_remove_space() [3].
According to the comment doc in ext4_ind_remove_space() the 'end' block
parameter needs to be one block after the last block to remove.
In the case when the BUG is triggered it points to the last block on
a 4GB virtual disk image. This is calculated in
ext4_ind_remove_space() in [4].
This patch adds a check that ensure the length + offest to be
within the valid range and returns -ENOSPC error code in case
it is invalid.
LINK: [1] https://syzkaller.appspot.com/bug?id=b80bd9cf348aac724a4f4dff251800106d721331
LINK: [2] https://syzkaller.appspot.com/text?tag=ReproC&x=14ba0238700000
LINK: [3] https://elixir.bootlin.com/linux/v5.17-rc8/source/fs/ext4/indirect.c#L1244
LINK: [4] https://elixir.bootlin.com/linux/v5.17-rc8/source/fs/ext4/indirect.c#L1234
Cc: Theodore Ts'o <[email protected]>
Cc: Andreas Dilger <[email protected]>
Cc: Ritesh Harjani <[email protected]>
Cc: <[email protected]>
Cc: <[email protected]>
Cc: <[email protected]>
Fixes: a4bb6b64e39a ("ext4: enable "punch hole" functionality")
Reported-by: [email protected]
Signed-off-by: Tadeusz Struk <[email protected]>
--
v2: Change sbi->s_blocksize to inode->i_sb->s_blocksize in maxlength
computation.
---
fs/ext4/inode.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 01c9e4f743ba..355384007d11 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3924,7 +3924,8 @@ int ext4_punch_hole(struct inode *inode, loff_t offset, loff_t length)
struct super_block *sb = inode->i_sb;
ext4_lblk_t first_block, stop_block;
struct address_space *mapping = inode->i_mapping;
- loff_t first_block_offset, last_block_offset;
+ loff_t first_block_offset, last_block_offset, max_length;
+ struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
handle_t *handle;
unsigned int credits;
int ret = 0, ret2 = 0;
@@ -3967,6 +3968,16 @@ int ext4_punch_hole(struct inode *inode, loff_t offset, loff_t length)
offset;
}
+ /*
+ * For punch hole the length + offset needs to be at least within
+ * one block before last
+ */
+ max_length = sbi->s_bitmap_maxbytes - inode->i_sb->s_blocksize;
+ if (offset + length >= max_length) {
+ ret = -ENOSPC;
+ goto out_mutex;
+ }
+
if (offset & (sb->s_blocksize - 1) ||
(offset + length) & (sb->s_blocksize - 1)) {
/*
--
2.35.1
Hi Ira,
On 3/22/22 09:37, Ira Weiny wrote:
> On Tue, Mar 15, 2022 at 02:54:39PM -0700, Tadeusz Struk wrote:
>> Syzbot found an issue [1] in ext4_fallocate().
>> The C reproducer [2] calls fallocate(), passing size 0xffeffeff000ul,
>> and offset 0x1000000ul, which, when added together exceed the disk size,
>> and trigger a BUG in ext4_ind_remove_space() [3].
>> According to the comment doc in ext4_ind_remove_space() the 'end' block
>> parameter needs to be one block after the last block to remove.
>> In the case when the BUG is triggered it points to the last block on
>> a 4GB virtual disk image. This is calculated in
>> ext4_ind_remove_space() in [4].
>> This patch adds a check that ensure the length + offest to be
>> within the valid range and returns -ENOSPC error code in case
>> it is invalid.
>
> Why is the check in vfs_fallocate() not working for this?
>
> https://elixir.bootlin.com/linux/v5.17-rc8/source/fs/open.c#L300
Good question. From reading the comment:
https://elixir.bootlin.com/linux/v5.17/source/fs/ext4/file.c#L225
it is possible that, for the bitmap-format, the limit might be smaller
than the s_maxbytes.
But even for a extent-mapped file the offest+len needs to be within the
first to last-1 block range for fallocate(fd, FALLOC_FL_PUNCH_HOLE, ...)
If it points to the last one then it is invalid, no?
The check you pointed to in vfs code checks if offest+len goes beyond
maximal file size.
> Also why do other file systems not fail? Is it because ext4 is special due to
> the end block needing to be one block after the last. That seems to imply the
> last block can't be used or there is some off by one issue somewhere?
According to the comment in
https://elixir.bootlin.com/linux/v5.17/source/fs/ext4/indirect.c#L1214
it has to be one block after the last to be removed.
--
Thanks,
Tadeusz
On Tue, Mar 15, 2022 at 02:54:39PM -0700, Tadeusz Struk wrote:
> Syzbot found an issue [1] in ext4_fallocate().
> The C reproducer [2] calls fallocate(), passing size 0xffeffeff000ul,
> and offset 0x1000000ul, which, when added together exceed the disk size,
> and trigger a BUG in ext4_ind_remove_space() [3].
> According to the comment doc in ext4_ind_remove_space() the 'end' block
> parameter needs to be one block after the last block to remove.
> In the case when the BUG is triggered it points to the last block on
> a 4GB virtual disk image. This is calculated in
> ext4_ind_remove_space() in [4].
> This patch adds a check that ensure the length + offest to be
> within the valid range and returns -ENOSPC error code in case
> it is invalid.
Why is the check in vfs_fallocate() not working for this?
https://elixir.bootlin.com/linux/v5.17-rc8/source/fs/open.c#L300
Also why do other file systems not fail? Is it because ext4 is special due to
the end block needing to be one block after the last. That seems to imply the
last block can't be used or there is some off by one issue somewhere?
Ira
>
> LINK: [1] https://syzkaller.appspot.com/bug?id=b80bd9cf348aac724a4f4dff251800106d721331
> LINK: [2] https://syzkaller.appspot.com/text?tag=ReproC&x=14ba0238700000
> LINK: [3] https://elixir.bootlin.com/linux/v5.17-rc8/source/fs/ext4/indirect.c#L1244
> LINK: [4] https://elixir.bootlin.com/linux/v5.17-rc8/source/fs/ext4/indirect.c#L1234
>
> Cc: Theodore Ts'o <[email protected]>
> Cc: Andreas Dilger <[email protected]>
> Cc: Ritesh Harjani <[email protected]>
> Cc: <[email protected]>
> Cc: <[email protected]>
> Cc: <[email protected]>
>
> Fixes: a4bb6b64e39a ("ext4: enable "punch hole" functionality")
> Reported-by: [email protected]
> Signed-off-by: Tadeusz Struk <[email protected]>
> --
> v2: Change sbi->s_blocksize to inode->i_sb->s_blocksize in maxlength
> computation.
> ---
> fs/ext4/inode.c | 13 ++++++++++++-
> 1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 01c9e4f743ba..355384007d11 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3924,7 +3924,8 @@ int ext4_punch_hole(struct inode *inode, loff_t offset, loff_t length)
> struct super_block *sb = inode->i_sb;
> ext4_lblk_t first_block, stop_block;
> struct address_space *mapping = inode->i_mapping;
> - loff_t first_block_offset, last_block_offset;
> + loff_t first_block_offset, last_block_offset, max_length;
> + struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
> handle_t *handle;
> unsigned int credits;
> int ret = 0, ret2 = 0;
> @@ -3967,6 +3968,16 @@ int ext4_punch_hole(struct inode *inode, loff_t offset, loff_t length)
> offset;
> }
>
> + /*
> + * For punch hole the length + offset needs to be at least within
> + * one block before last
> + */
> + max_length = sbi->s_bitmap_maxbytes - inode->i_sb->s_blocksize;
> + if (offset + length >= max_length) {
> + ret = -ENOSPC;
> + goto out_mutex;
> + }
> +
> if (offset & (sb->s_blocksize - 1) ||
> (offset + length) & (sb->s_blocksize - 1)) {
> /*
> --
> 2.35.1
>
On 3/15/22 14:54, Tadeusz Struk wrote:
> Syzbot found an issue [1] in ext4_fallocate().
> The C reproducer [2] calls fallocate(), passing size 0xffeffeff000ul,
> and offset 0x1000000ul, which, when added together exceed the disk size,
> and trigger a BUG in ext4_ind_remove_space() [3].
> According to the comment doc in ext4_ind_remove_space() the 'end' block
> parameter needs to be one block after the last block to remove.
> In the case when the BUG is triggered it points to the last block on
> a 4GB virtual disk image. This is calculated in
> ext4_ind_remove_space() in [4].
> This patch adds a check that ensure the length + offest to be
> within the valid range and returns -ENOSPC error code in case
> it is invalid.
Hi,
Any feedback on this?
--
Thanks,
Tadeusz
On Tue, Mar 15, 2022 at 02:54:39PM -0700, Tadeusz Struk wrote:
> @@ -3967,6 +3968,16 @@ int ext4_punch_hole(struct inode *inode, loff_t offset, loff_t length)
> offset;
> }
>
> + /*
> + * For punch hole the length + offset needs to be at least within
> + * one block before last
> + */
> + max_length = sbi->s_bitmap_maxbytes - inode->i_sb->s_blocksize;
> + if (offset + length >= max_length) {
> + ret = -ENOSPC;
> + goto out_mutex;
> + }
I wonder if we would be better off just simply capping length to
max_length? If length is set to some large value, such as LONG_MAX,
it's pretty clear what the intention should be, which is to simply do
the equivalent of truncating the file at offset. Perhaps we should
just do that?
That being said, we should be consistent with what other file systems
do when they are asked to punch a hole starting at offset and
extending out to LONG_MAX.
Also, if we are going to return an error, I don't think ENOSPC is the
correct error to be returning.
- Ted