[PATCH] btfrs: initialize return of btrfs_extent_same

[PATCH] btfrs: initialize return of btrfs_extent_same

[trix]

From: Tom Rix <trix@redhat.com>

clang static analysis flags a garbage return

fs/btrfs/reflink.c:611:2: warning: Undefined or garbage value returned to caller [core.uninitialized.UndefReturn]
        return ret;
        ^~~~~~~~~~
ret will not be set when olen is 0
When olen is 0, this function does no work.

So initialize ret to 0

Signed-off-by: Tom Rix <trix@redhat.com>
---
 fs/btrfs/reflink.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/reflink.c b/fs/btrfs/reflink.c
index 040009d1cc31..200a80fcbecb 100644
--- a/fs/btrfs/reflink.c
+++ b/fs/btrfs/reflink.c
@@ -572,7 +572,7 @@ static int btrfs_extent_same_range(struct inode *src, u64 loff, u64 len,
 static int btrfs_extent_same(struct inode *src, u64 loff, u64 olen,
 			     struct inode *dst, u64 dst_loff)
 {
-	int ret;
+	int ret = 0;
 	u64 i, tail_len, chunk_count;
 	struct btrfs_root *root_dst = BTRFS_I(dst)->root;
 
-- 
2.18.1

Re: [PATCH] btfrs: initialize return of btrfs_extent_same

[Nikolay Borisov]

On 5.07.20 г. 17:20 ч., trix@redhat.com wrote:
> From: Tom Rix <trix@redhat.com>
> 
> clang static analysis flags a garbage return
> 
> fs/btrfs/reflink.c:611:2: warning: Undefined or garbage value returned to caller [core.uninitialized.UndefReturn]
>         return ret;
>         ^~~~~~~~~~
> ret will not be set when olen is 0
> When olen is 0, this function does no work.
> 
> So initialize ret to 0
> 
> Signed-off-by: Tom Rix <trix@redhat.com>

Patch itself is good however, the bug cannot currently be triggered, due
to the following code in the sole caller (btrfs_remap_file_range):



   15         if (ret < 0 || len == 0)

   14                 goto out_unlock;

   13

   12         if (remap_flags & REMAP_FILE_DEDUP)

   11                 ret = btrfs_extent_same(src_inode, off, len,
dst_inode, destoff);
   10         else

    9                 ret = btrfs_clone_files(dst_file, src_file, off,
len, destoff);



i.e len is guaranteed to be non-zero

> ---
>  fs/btrfs/reflink.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/reflink.c b/fs/btrfs/reflink.c
> index 040009d1cc31..200a80fcbecb 100644
> --- a/fs/btrfs/reflink.c
> +++ b/fs/btrfs/reflink.c
> @@ -572,7 +572,7 @@ static int btrfs_extent_same_range(struct inode *src, u64 loff, u64 len,
>  static int btrfs_extent_same(struct inode *src, u64 loff, u64 olen,
>  			     struct inode *dst, u64 dst_loff)
>  {
> -	int ret;
> +	int ret = 0;
>  	u64 i, tail_len, chunk_count;
>  	struct btrfs_root *root_dst = BTRFS_I(dst)->root;
>  
> 

Re: [PATCH] btfrs: initialize return of btrfs_extent_same

[Nikolay Borisov]

On 5.07.20 г. 17:20 ч., trix@redhat.com wrote:
> From: Tom Rix <trix@redhat.com>
> 
> clang static analysis flags a garbage return
> 
> fs/btrfs/reflink.c:611:2: warning: Undefined or garbage value returned to caller [core.uninitialized.UndefReturn]
>         return ret;
>         ^~~~~~~~~~
> ret will not be set when olen is 0
> When olen is 0, this function does no work.
> 
> So initialize ret to 0
> 
> Signed-off-by: Tom Rix <trix@redhat.com>

And I forgot:

Reviewed-by: Nikolay Borisov <nborisov@suse.com>

> ---
>  fs/btrfs/reflink.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/reflink.c b/fs/btrfs/reflink.c
> index 040009d1cc31..200a80fcbecb 100644
> --- a/fs/btrfs/reflink.c
> +++ b/fs/btrfs/reflink.c
> @@ -572,7 +572,7 @@ static int btrfs_extent_same_range(struct inode *src, u64 loff, u64 len,
>  static int btrfs_extent_same(struct inode *src, u64 loff, u64 olen,
>  			     struct inode *dst, u64 dst_loff)
>  {
> -	int ret;
> +	int ret = 0;
>  	u64 i, tail_len, chunk_count;
>  	struct btrfs_root *root_dst = BTRFS_I(dst)->root;
>  
> 

Re: [PATCH] btfrs: initialize return of btrfs_extent_same

[David Sterba]

On Sun, Jul 05, 2020 at 05:48:17PM +0300, Nikolay Borisov wrote:
> On 5.07.20 г. 17:20 ч., trix@redhat.com wrote:
> > From: Tom Rix <trix@redhat.com>
> > 
> > clang static analysis flags a garbage return
> > 
> > fs/btrfs/reflink.c:611:2: warning: Undefined or garbage value returned to caller [core.uninitialized.UndefReturn]
> >         return ret;
> >         ^~~~~~~~~~
> > ret will not be set when olen is 0
> > When olen is 0, this function does no work.
> > 
> > So initialize ret to 0
> > 
> > Signed-off-by: Tom Rix <trix@redhat.com>
> 
> Patch itself is good however, the bug cannot currently be triggered, due
> to the following code in the sole caller (btrfs_remap_file_range):
> 
> 
> 
>    15         if (ret < 0 || len == 0)
>    14                 goto out_unlock;
>    13
>    12         if (remap_flags & REMAP_FILE_DEDUP)
>    11                 ret = btrfs_extent_same(src_inode, off, len, dst_inode, destoff);
>    10         else
>     9                 ret = btrfs_clone_files(dst_file, src_file, off,
> len, destoff);
> 
> i.e len is guaranteed to be non-zero

Yeah, for that reason I don't think we need to set the value inside
btrfs_extent_same because the caller(s) do the sanity checks.

There are VFS-level checks of the length wrt zero, eg. it won't even
call to copy_file_range from vfs_copy_file_range. The user supplied
length = 0 is interpreted as 'until the end of file' and is properly
reclaculated in generic_remap_file_range_prep.

This looks like clang checker is not able to follow the values accross
function calls, even if the functions are static.