Jeff Layton (jlayton@xxxxxxxxxx) wrote:
> sb->s_maxbytes is supposed to indicate the maximum size of a file that
> can exist on the filesystem. It's declared as an unsigned long long.
>
> Even if a filesystem has no inherent limit that prevents it from using
> every bit in that unsigned long long, it's still problematic to set it
> to anything larger than MAX_LFS_FILESIZE. There are places in the kernel
> that cast s_maxbytes to a signed value. If it's set too large then this
> cast makes it a negative number and generally breaks the comparison.
>
> Change s_maxbytes to be loff_t instead. That should help eliminate the
> temptation to set it too large by making it a signed value.
>
> Also, add a warning for couple of releases to help catch filesystems
> that set s_maxbytes too large. Eventually we can either convert this to
> a BUG() or just remove it and in the hope that no one will get it wrong
> now that it's a signed value.
>
> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> ---
> fs/super.c | 10 ++++++++++
> include/linux/fs.h | 2 +-
> 2 files changed, 11 insertions(+), 1 deletions(-)
>
> diff --git a/fs/super.c b/fs/super.c
> index 2761d3e..660d437 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -889,6 +889,16 @@ vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void
> if (error)
> goto out_sb;
>
> + /*
> + * filesystems should never set s_maxbytes larger than MAX_LFS_FILESIZE
> + * but s_maxbytes was an unsigned long long for many releases. Throw
> + * this warning for a little while to try and catch filesystems that
> + * violate this rule. This warning should be either removed or
> + * converted to a BUG() in 2.6.34.
> + */
> + WARN((mnt->mnt_sb->s_maxbytes < 0), "WARNING: %s set sb->s_maxbytes to "
> + "negative value (%lld)\n", type->name, mnt->mnt_sb->s_maxbytes);
> +
Minor nit. "WARNING:" is redundant. I believe WARN() will already print
"WARNING: at <file>:<line>".
> mnt->mnt_mountpoint = mnt->mnt_root;
> mnt->mnt_parent = mnt;
> up_write(&mnt->mnt_sb->s_umount);
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 67888a9..bfe3c08 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1316,7 +1316,7 @@ struct super_block {
> unsigned long s_blocksize;
> unsigned char s_blocksize_bits;
> unsigned char s_dirt;
> - unsigned long long s_maxbytes; /* Max file size */
> + loff_t s_maxbytes; /* Max file size */
Looks good to me. Thanks!
> struct file_system_type *s_type;
> const struct super_operations *s_op;
> struct dquot_operations *dq_op;
> --
> 1.6.0.6
>
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