Re: [PATCH] fix offset checks in do_sendfile to use unsigned values

[Johannes Weiner <hannes@cmpxchg.org>]

On Wed, Jul 22, 2009 at 07:28:19AM -0400, Jeff Layton wrote:
> If do_sendfile is called with a "max" value of 0, it grabs the lesser
> s_maxbytes value of the two superblocks to use instead. There's a
> problem here however. s_maxbytes is an unsigned long long and it gets
> cast to a signed value. If both s_maxbytes values are large enough, max
> will end up being negative and the comparisons in this code won't work
> correctly.
> 
> Change do_sendfile to use unsigned values internally for the offset
> checks.
> 
> Signed-off-by: Jeff Layton <jlayton@redhat.com>
> ---
>  fs/read_write.c |    6 +++---
>  1 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/read_write.c b/fs/read_write.c
> index 6c8c55d..36899ff 100644
> --- a/fs/read_write.c
> +++ b/fs/read_write.c
> @@ -788,11 +788,11 @@ SYSCALL_DEFINE5(pwritev, unsigned long, fd, const struct iovec __user *, vec,
>  }
>  
>  static ssize_t do_sendfile(int out_fd, int in_fd, loff_t *ppos,
> -			   size_t count, loff_t max)
> +			   size_t count, unsigned long long max)
>  {
>  	struct file * in_file, * out_file;
>  	struct inode * in_inode, * out_inode;
> -	loff_t pos;
> +	unsigned long long pos;
>  	ssize_t retval;
>  	int fput_needed_in, fput_needed_out, fl;
>  
> @@ -838,7 +838,7 @@ static ssize_t do_sendfile(int out_fd, int in_fd, loff_t *ppos,
>  	if (!max)
>  		max = min(in_inode->i_sb->s_maxbytes, out_inode->i_sb->s_maxbytes);
>  
> -	pos = *ppos;
> +	pos = (unsigned long long) *ppos;
>  	retval = -EINVAL;
>  	if (unlikely(pos < 0))
>  		goto fput_out;

May it be possible that cifs is the only fs that sets sb->sb_maxbytes
to exceed loff_t?  It seems the others clamp it to MAX_LFS_FILESIZE
while CIFS exceeds this by one.  And then max is -1.

So, isn't the correct fix something similar to this?

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index e16d759..df56093 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -2452,10 +2452,10 @@ try_mount_again:
 		tcon->local_lease = volume_info->local_lease;
 	}
 	if (pSesInfo) {
-		if (pSesInfo->capabilities & CAP_LARGE_FILES) {
-			sb->s_maxbytes = (u64) 1 << 63;
-		} else
-			sb->s_maxbytes = (u64) 1 << 31;	/* 2 GB */
+		if (pSesInfo->capabilities & CAP_LARGE_FILES)
+			sb->s_maxbytes = MAX_LFS_FILESIZE;
+		else
+			sb->s_maxbytes = MAX_NON_LFS;
 	}
 
 	/* BB FIXME fix time_gran to be larger for LANMAN sessions */