On 09/22/2015 06:20 PM, Stephen Smalley wrote: > This improves the robustness of programs using selinux_check_access() > in the face of policy updates that alter the values of the class or > permissions that they are checking. Otherwise, a policy update can > trigger false permission denials, as in > https://bugzilla.redhat.com/show_bug.cgi?id=1264051
Thank you, Stephen. I've applied it to Fedora 23 and Rawhide and prepared scratch builds [1] and according to my testing it fixes the problem. So after a little more testing I'll push it to Fedoras. [1] http://koji.fedoraproject.org/koji/taskinfo?taskID=11276795 http://koji.fedoraproject.org/koji/taskinfo?taskID=11275234 Petr > Changes to the userspace class/permission definitions should still be > handled with care, as not all userspace object managers have been converted > to use selinux_check_access() and even those that do use it are still not > entirely safe against an interleaving of a policy reload and a call to > selinux_check_access(). The change does however address the issue in > the above bug and avoids the need to restart systemd. > > This change restores the flush_class_cache() function that was removed in > commit 435fae64a931 ("libselinux: Remove unused flush_class_cache method") > because it had no users at the time, but makes it hidden to avoid exposing > it as part of the libselinux ABI. > > Signed-off-by: Stephen Smalley <[email protected]> > --- > v2 fixes various whitespace and style issues. > > libselinux/src/checkAccess.c | 27 ++++++++++++++++++++++----- > libselinux/src/selinux_internal.h | 2 ++ > libselinux/src/stringrep.c | 22 ++++++++++++++++++++++ > 3 files changed, 46 insertions(+), 5 deletions(-) > > diff --git a/libselinux/src/checkAccess.c b/libselinux/src/checkAccess.c > index 29be16e..8de5747 100644 > --- a/libselinux/src/checkAccess.c > +++ b/libselinux/src/checkAccess.c > @@ -10,11 +10,26 @@ > static pthread_once_t once = PTHREAD_ONCE_INIT; > static int selinux_enabled; > > +static int avc_reset_callback(uint32_t event __attribute__((unused)), > + security_id_t ssid __attribute__((unused)), > + security_id_t tsid __attribute__((unused)), > + security_class_t tclass __attribute__((unused)), > + access_vector_t perms __attribute__((unused)), > + access_vector_t *out_retained __attribute__((unused))) > +{ > + flush_class_cache(); > + return 0; > +} > + > static void avc_init_once(void) > { > selinux_enabled = is_selinux_enabled(); > - if (selinux_enabled == 1) > - avc_open(NULL, 0); > + if (selinux_enabled == 1) { > + if (avc_open(NULL, 0)) > + return; > + avc_add_callback(avc_reset_callback, AVC_CALLBACK_RESET, > + 0, 0, 0, 0); > + } > } > > int selinux_check_access(const char *scon, const char *tcon, const char > *class, const char *perm, void *aux) { > @@ -33,9 +48,11 @@ int selinux_check_access(const char *scon, const char > *tcon, const char *class, > if (rc < 0) > return rc; > > - rc = avc_context_to_sid(tcon, &tcon_id); > - if (rc < 0) > - return rc; > + rc = avc_context_to_sid(tcon, &tcon_id); > + if (rc < 0) > + return rc; > + > + (void) avc_netlink_check_nb(); > > sclass = string_to_security_class(class); > if (sclass == 0) { > diff --git a/libselinux/src/selinux_internal.h > b/libselinux/src/selinux_internal.h > index 844e408..46566f6 100644 > --- a/libselinux/src/selinux_internal.h > +++ b/libselinux/src/selinux_internal.h > @@ -102,6 +102,8 @@ hidden_proto(security_get_initial_context); > hidden_proto(security_get_initial_context_raw); > hidden_proto(selinux_reset_config); > > +hidden void flush_class_cache(void); > + > extern int load_setlocaldefs hidden; > extern int require_seusers hidden; > extern int selinux_page_size hidden; > diff --git a/libselinux/src/stringrep.c b/libselinux/src/stringrep.c > index 9ae8248..2dbec2b 100644 > --- a/libselinux/src/stringrep.c > +++ b/libselinux/src/stringrep.c > @@ -158,6 +158,28 @@ err1: > return NULL; > } > > +hidden void flush_class_cache(void) > +{ > + struct discover_class_node *cur = discover_class_cache, *prev = NULL; > + size_t i; > + > + while (cur != NULL) { > + free(cur->name); > + > + for (i = 0; i < MAXVECTORS; i++) > + free(cur->perms[i]); > + > + free(cur->perms); > + > + prev = cur; > + cur = cur->next; > + > + free(prev); > + } > + > + discover_class_cache = NULL; > +} > + > security_class_t string_to_security_class(const char *s) > { > struct discover_class_node *node; >
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