Re: [PATCH] cifs: fix memory leak in smb3_fs_context_parse_param error path

[Paulo Alcantara <pc@manguebit.org>]

ssrane_b23@ee.vjti.ac.in writes:

> From: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
>
> Add proper cleanup of ctx->source and fc->source to the
> cifs_parse_mount_err error handler. This ensures that memory allocated
> for the source strings is correctly freed on all error paths, matching
> the cleanup already performed in the success path by
> smb3_cleanup_fs_context_contents().
> Pointers are also set to NULL after freeing to prevent potential
> double-free issues.
>
> This change fixes a memory leak originally detected by syzbot. The
> leak occurred when processing Opt_source mount options if an error
> happened after ctx->source and fc->source were successfully
> allocated but before the function completed.
>
> The specific leak sequence was:
> 1. ctx->source = smb3_fs_context_fullpath(ctx, '/') allocates memory
> 2. fc->source = kstrdup(ctx->source, GFP_KERNEL) allocates more memory
> 3. A subsequent error jumps to cifs_parse_mount_err
> 4. The old error handler freed passwords but not the source strings,
> causing the memory to leak.
>
> This issue was not addressed by commit e8c73eb7db0a ("cifs: client:
> fix memory leak in smb3_fs_context_parse_param"), which only fixed
> leaks from repeated fsconfig() calls but not this error path.
>
> Reported-by: syzbot+87be6809ed9bf6d718e3@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=87be6809ed9bf6d718e3
> Fixes: 24e0a1eff9e2 ("cifs: switch to new mount api")
> Signed-off-by: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
> ---
>  fs/smb/client/fs_context.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/fs/smb/client/fs_context.c b/fs/smb/client/fs_context.c
> index 0f894d09157b..975f1fa153fd 100644
> --- a/fs/smb/client/fs_context.c
> +++ b/fs/smb/client/fs_context.c
> @@ -1834,6 +1834,12 @@ static int smb3_fs_context_parse_param(struct fs_context *fc,
>  	ctx->password = NULL;
>  	kfree_sensitive(ctx->password2);
>  	ctx->password2 = NULL;
> +	kfree(ctx->source);
> +	ctx->source = NULL;
> +	if (fc) {
> +		kfree(fc->source);
> +		fc->source = NULL;
> +	}

The non-NULL check of @fc makes no sense.

Otherwise looks good:

Reviewed-by: Paulo Alcantara (Red Hat) <pc@manguebit.org>