[pacman-dev] [PATCH v2] Fallback to detached signatures during keyring check

Anatol Pomozov anatol.pomozov at gmail.com
Sun May 31 08:37:00 UTC 2020


Hi Andrew, thank you for the quick response

On Sat, May 30, 2020 at 9:31 PM Andrew Gregory
<andrew.gregory.8 at gmail.com> wrote:
>
> On 05/30/20 at 07:51pm, Anatol Pomozov wrote:
> > Pacman has a 'key in keyring' verification step that makes sure the signatures
> > have a valid keyid. Currently pacman parses embedded package signatures only.
> >
> > Add a fallback to detached signatures. If embedded signature is missing then it
> > tries to read corresponding *.sig file and get keyid from there.
> >
> > Verification:
> >   debug: found cached pkg: /var/cache/pacman/pkg/glib-networking-2.64.3-1-x86_64.pkg.tar.zst
> >   debug: found detached signature /var/cache/pacman/pkg/glib-networking-2.64.3-1-x86_64.pkg.tar.zst.sig with size 310
> >   debug: found signature key: A5E9288C4FA415FA
> >   debug: looking up key A5E9288C4FA415FA locally
> >   debug: key lookup success, key exists
> >
> > Signed-off-by: Anatol Pomozov <anatol.pomozov at gmail.com>
> > ---
> >  lib/libalpm/alpm.h    | 10 ++++++++++
> >  lib/libalpm/package.c | 31 +++++++++++++++++++++++++++++++
> >  lib/libalpm/sync.c    | 17 ++++++++---------
> >  lib/libalpm/util.c    | 35 +++++++++++++++++++++++++++++++++++
> >  lib/libalpm/util.h    |  1 +
> >  5 files changed, 85 insertions(+), 9 deletions(-)
> >
> > diff --git a/lib/libalpm/alpm.h b/lib/libalpm/alpm.h
> > index c6a13273..9c5fff73 100644
> > --- a/lib/libalpm/alpm.h
> > +++ b/lib/libalpm/alpm.h
> > @@ -1403,6 +1403,16 @@ alpm_db_t *alpm_pkg_get_db(alpm_pkg_t *pkg);
> >   */
> >  const char *alpm_pkg_get_base64_sig(alpm_pkg_t *pkg);
> >
> > +/** Extracts package signature either from embedded package signature
> > + * or if it is absent then reads data from detached signature file.
> > + * @param pkg a pointer to package
> > + * @param sig output parameter for signature data. Callee function allocates
> > + * buffer needed for the signature data. Caller is responsible for
> > + * freeing this buffer.
> > + * @return size of a signature or negative number if error.
> > + */
> > +int alpm_pkg_get_sig(alpm_pkg_t *pkg, unsigned char **sig);
> > +
> >  /** Returns the method used to validate a package during install.
> >   * @param pkg a pointer to package
> >   * @return an enum member giving the validation method
> > diff --git a/lib/libalpm/package.c b/lib/libalpm/package.c
> > index 5c5fa073..e0e4d987 100644
> > --- a/lib/libalpm/package.c
> > +++ b/lib/libalpm/package.c
> > @@ -268,6 +268,37 @@ const char SYMEXPORT *alpm_pkg_get_base64_sig(alpm_pkg_t *pkg)
> >       return pkg->base64_sig;
> >  }
> >
> > +int SYMEXPORT alpm_pkg_get_sig(alpm_pkg_t *pkg, unsigned char **sig)
>
> This API is weird, why are you returning an int when neither of the
> successful values are int and can potentially overflow an int?  You're
> returning the length of an allocated string, size_t is the appropriate
> type.

size_t is unsigned int. But this function returns positive length in
case of successful signature read or negative value in case of error.
Thus return value cannot be size_t.

>
> > +{
> > +     ASSERT(pkg != NULL, return -1);
> > +     pkg->handle->pm_errno = ALPM_ERR_OK;
>
> I don't like clearing pm_errno without a good reason.  It generally
> doesn't serve any purpose and can get us into trouble if a function
> gets called during cleanup somewhere.

I personally do not feel that "pm_errno = ALPM_ERR_OK" is useful here
and I am more than happy to remove it.

But I also I see this pattern is used a lot. Only this file
(lib/libalpm/package.c) has like 20 use-cases of it. e.g.

off_t SYMEXPORT alpm_pkg_get_isize(alpm_pkg_t *pkg)
{
        ASSERT(pkg != NULL, return -1);
        pkg->handle->pm_errno = ALPM_ERR_OK;
        return pkg->ops->get_isize(pkg);
}

So I was trying to follow a standard practice here. Or are you trying
to say that lib/libalpm/package.c examples I was looking at are
incorrect?

>
> > +     if(pkg->base64_sig) {
> > +             size_t sig_len;
> > +             int ret = alpm_decode_signature(pkg->base64_sig, sig, &sig_len);
> > +             return ret == 0 ? (int)sig_len : -1;
> > +     } else {
> > +             char *pkgpath, *sigpath;
> > +             int len;
> > +
> > +             pkgpath = _alpm_filecache_find(pkg->handle, pkg->filename);
> > +             if(!pkgpath) {
> > +                     RET_ERR(pkg->handle, ALPM_ERR_PKG_NOT_FOUND, -1);
> > +             }
> > +             sigpath = _alpm_sigpath(pkg->handle, pkgpath);
> > +             if(!sigpath || _alpm_access(pkg->handle, NULL, sigpath, R_OK)) {
> > +                     FREE(pkgpath);
> > +                     FREE(sigpath);
> > +                     RET_ERR(pkg->handle, ALPM_ERR_SIG_MISSING, -1);
> > +             }
> > +             len = _alpm_read_file(sigpath, sig);
>
> You need to check for and handle failure.

Do you mean to handle a file read failure? But both successful and
erroneous codepaths are the same - free() the resources and return
"len".

> > +             _alpm_log(pkg->handle, ALPM_LOG_DEBUG, "found detached signature %s with size %d\n", sigpath, len);
> > +             FREE(pkgpath);
> > +             FREE(sigpath);
> > +             return len;
> > +     }
> > +}
> > +
> >  const char SYMEXPORT *alpm_pkg_get_arch(alpm_pkg_t *pkg)
> >  {
> >       ASSERT(pkg != NULL, return NULL);
> > diff --git a/lib/libalpm/sync.c b/lib/libalpm/sync.c
> > index 8c01ad95..0ab0fe26 100644
> > --- a/lib/libalpm/sync.c
> > +++ b/lib/libalpm/sync.c
> > @@ -880,18 +880,17 @@ static int check_keyring(alpm_handle_t *handle)
> >               }
> >
> >               level = alpm_db_get_siglevel(alpm_pkg_get_db(pkg));
> > -             if((level & ALPM_SIG_PACKAGE) && pkg->base64_sig) {
> > -                     unsigned char *decoded_sigdata = NULL;
> > -                     size_t data_len;
> > -                     int decode_ret = alpm_decode_signature(pkg->base64_sig,
> > -                                     &decoded_sigdata, &data_len);
> > -                     if(decode_ret == 0) {
> > +             if((level & ALPM_SIG_PACKAGE)) {
> > +                     unsigned char *signature = NULL;
> > +                     int sig_len = alpm_pkg_get_sig(pkg, &signature);
> > +                     if(sig_len > 0) {
> >                               alpm_list_t *keys = NULL;
> > -                             if(alpm_extract_keyid(handle, pkg->name, decoded_sigdata,
> > -                                                     data_len, &keys) == 0) {
> > +                             if(alpm_extract_keyid(handle, pkg->name, signature,
> > +                                                     sig_len, &keys) == 0) {
> >                                       alpm_list_t *k;
> >                                       for(k = keys; k; k = k->next) {
> >                                               char *key = k->data;
> > +                                             _alpm_log(handle, ALPM_LOG_DEBUG, "found signature key: %s\n", key);
> >                                               if(!alpm_list_find(errors, key, key_cmp) &&
> >                                                               _alpm_key_in_keychain(handle, key) == 0) {
> >                                                       keyinfo = malloc(sizeof(struct keyinfo_t));
> > @@ -905,8 +904,8 @@ static int check_keyring(alpm_handle_t *handle)
> >                                       }
> >                                       FREELIST(keys);
> >                               }
> > -                             free(decoded_sigdata);
> >                       }
> > +                     free(signature);
> >               }
> >       }
> >
> > diff --git a/lib/libalpm/util.c b/lib/libalpm/util.c
> > index 76728eb4..3d57817b 100644
> > --- a/lib/libalpm/util.c
> > +++ b/lib/libalpm/util.c
> > @@ -1489,3 +1489,38 @@ void _alpm_alloc_fail(size_t size)
> >  {
> >       fprintf(stderr, "alloc failure: could not allocate %zu bytes\n", size);
> >  }
> > +
> > +/** This functions reads file content.
> > + *
> > + * Memory buffer is allocated by the callee function. It is responsibility
> > + * of the caller to free the buffer
> > + *
> > + * @param filepath filepath to read
> > + * @param data pointer to output buffer
> > + * @return size of the data read or negative number in case of error
> > + */
> > +int _alpm_read_file(const char *filepath, unsigned char **data)
>
> Same as above.
>
> > +{
> > +     struct stat st;
> > +     FILE *fp;
> > +
> > +     if((fp = fopen(filepath, "rb")) == NULL) {
> > +             return -1;
> > +     }
> > +
> > +     if(fstat(fileno(fp), &st) != 0) {
> > +             fclose(fp);
> > +             return -1;
> > +     }
> > +
> > +     MALLOC(*data, st.st_size, fclose(fp); return -1);
> > +
> > +     if(fread(*data, st.st_size, 1, fp) != 1) {
> > +             FREE(*data);
> > +             fclose(fp);
> > +             return -1;
> > +     }
> > +
> > +     fclose(fp);
> > +     return st.st_size;
> > +}
> > diff --git a/lib/libalpm/util.h b/lib/libalpm/util.h
> > index 4fc6e718..50a94489 100644
> > --- a/lib/libalpm/util.h
> > +++ b/lib/libalpm/util.h
> > @@ -155,6 +155,7 @@ int _alpm_fnmatch_patterns(alpm_list_t *patterns, const char *string);
> >  int _alpm_fnmatch(const void *pattern, const void *string);
> >  void *_alpm_realloc(void **data, size_t *current, const size_t required);
> >  void *_alpm_greedy_grow(void **data, size_t *current, const size_t required);
> > +int _alpm_read_file(const char *filepath, unsigned char **data);
> >
> >  #ifndef HAVE_STRSEP
> >  char *strsep(char **, const char *);
> > --
> > 2.26.2


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