[pacman-dev] [PATCH v2] Fix handling of unavailable backup hashes

[Andrew Gregory]

On 04/11/16 at 10:51am, Will Miles wrote:
> This patch fixes several places where an unavailable (NULL) backup hash may be
> passed to a printf() call, which segfaults on some libcs.  This includes
> local database writes where unavailable hashes are represented by the file
> name only.  This condition may occur when an updated package changes the
> contents of its backup=() list.
> 
> Signed-off-by: Will Miles <wmiles at sgl.com>
> ---
>  lib/libalpm/add.c      | 6 +++---
>  lib/libalpm/be_local.c | 6 +++++-
>  2 files changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/lib/libalpm/add.c b/lib/libalpm/add.c
> index f5c9a95..629e2a5 100644
> --- a/lib/libalpm/add.c
> +++ b/lib/libalpm/add.c
> @@ -339,9 +339,9 @@ static int extract_single_file(alpm_handle_t *handle, struct archive *archive,
>  		hash_pkg = backup ? backup->hash : alpm_compute_md5sum(filename);
>  
>  		_alpm_log(handle, ALPM_LOG_DEBUG, "checking hashes for %s\n", origfile);
> -		_alpm_log(handle, ALPM_LOG_DEBUG, "current:  %s\n", hash_local);
> -		_alpm_log(handle, ALPM_LOG_DEBUG, "new:      %s\n", hash_pkg);
> -		_alpm_log(handle, ALPM_LOG_DEBUG, "original: %s\n", hash_orig);
> +		_alpm_log(handle, ALPM_LOG_DEBUG, "current:  %s\n", (hash_local ? hash_local : "NULL") );
> +		_alpm_log(handle, ALPM_LOG_DEBUG, "new:      %s\n", (hash_pkg ? hash_pkg : "NULL") );
> +		_alpm_log(handle, ALPM_LOG_DEBUG, "original: %s\n", (hash_orig ? hash_orig : "NULL") );
>  
>  		if(hash_local && hash_pkg && strcmp(hash_local, hash_pkg) == 0) {
>  			/* local and new files are the same, updating anyway to get
> diff --git a/lib/libalpm/be_local.c b/lib/libalpm/be_local.c
> index f817822..21166cb 100644
> --- a/lib/libalpm/be_local.c
> +++ b/lib/libalpm/be_local.c
> @@ -1037,7 +1037,11 @@ int _alpm_local_db_write(alpm_db_t *db, alpm_pkg_t *info, alpm_dbinfrq_t inforeq
>  			fputs("%BACKUP%\n", fp);
>  			for(lp = info->backup; lp; lp = lp->next) {
>  				const alpm_backup_t *backup = lp->data;
> -				fprintf(fp, "%s\t%s\n", backup->name, backup->hash);
> +				if (backup->hash) {
> +					fprintf(fp, "%s\t%s\n", backup->name, backup->hash);
> +				} else {
> +					fprintf(fp, "%s\n", backup->name);

This will break the parser if the file name contains a tab.  Just do
something similar to what you did above:

 fprintf(fp, "%s\t%s\n", backup->name, backup->hash ? backup->hash : "");

The parser also needs to be updated to use strrchr instead of strchr
for the same reason, but that's another patch.

> +				}
>  			}
>  			fputc('\n', fp);
>  		}
> -- 
> 2.6.3