On Tue, Jul 14, 2020 at 06:05:09AM -0700, trix@xxxxxxxxxx wrote:
> From: Tom Rix <trix@xxxxxxxxxx>
>
> clang static analysis flags this error
>
> inode.c:1083:5: warning: Argument to kfree() is the address of the
> local variable 'unf_single', which is not memory allocated by
> malloc() [unix.Malloc]
> kfree(un);
> ^~~~~~~~~
> Assignment of 'un'
>
> /*
> * We use this in case we need to allocate
> * only one block which is a fastpath
> */
> unp_t unf_single = 0;
>
> ...
>
> if (blocks_needed == 1) {
> un = &unf_single;
> } else {
> un = kcalloc(min(blocks_needed, max_to_insert),
> UNFM_P_SIZE, GFP_NOFS);
> if (!un) {
> un = &unf_single;
> blocks_needed = 1;
> max_to_insert = 0;
> }
> }
>
> The logic to free 'un'
>
> if (blocks_needed != 1)
> kfree(un);
>
> Because the kcalloc failure falls back to using unf_single,
> the if-check for the free is wrong.
I think you mean "Because clang's static analysis is limited, it
warns incorrectly about this". There's no path to get to the
kfree with blocks_needed != 1 and un being equal to &unf_single.
> So improve the check.
>
> Signed-off-by: Tom Rix <trix@xxxxxxxxxx>
> ---
> fs/reiserfs/inode.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/reiserfs/inode.c b/fs/reiserfs/inode.c
> index 1509775da040..4d62148e43e6 100644
> --- a/fs/reiserfs/inode.c
> +++ b/fs/reiserfs/inode.c
> @@ -1079,7 +1079,7 @@ int reiserfs_get_block(struct inode *inode, sector_t block,
> UNFM_P_SIZE *
> blocks_needed);
>
> - if (blocks_needed != 1)
> + if (un != &unf_single)
> kfree(un);
I don't actually object to this patch, but your analysis of clang's
analysis is wrong.
