alexk / rpms / rpm

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From 57aa660de4d1b8375cd56f7b8b5fcaf8ad9a5af7 Mon Sep 17 00:00:00 2001
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From: chantra <chantr4@gmail.com>
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Date: Fri, 25 Mar 2022 08:13:08 -0700
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Subject: [PATCH 28/30] [reflink] remove requirement for executable stack flag
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reflink was calling `bsearch` with a nested function comparator which
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make GCC require the executable stack flag (see `man execstack`).
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selinux prevents the use of this flag:
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```
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error: Failed to dlopen /usr/lib64/rpm-plugins/reflink.so
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/usr/lib64/rpm-plugins/reflink.so: cannot enable executable stack as
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shared object requires: Permission denied
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```
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To fix this, either rpm could be granted the correct selinux permission,
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but this would open up execstack for more the whole rpm process.
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Fundamentally, this is happening because there is no re-entrant version
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of `bsearch`. We could probably use a global variable and be done with
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it given that each rpm is processed sequencially, but that contract may
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not hold true for ever.
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Here we are copying stdlib's `bsearch` and making it re-entrant by
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allowing to pass an void * data parameter where we can pass the key
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size.
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After applying this patch, when reflink.o is installed, it has the executable
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flag cleared:
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```
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- /usr/lib64/rpm-plugins/reflink.so
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```
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---
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 plugins/reflink.c | 60 +++++++++++++++++++++++++++++++++++++----------
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 1 file changed, 48 insertions(+), 12 deletions(-)
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diff --git a/plugins/reflink.c b/plugins/reflink.c
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index 4fc1d74d1..69e6b51e6 100644
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--- a/plugins/reflink.c
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+++ b/plugins/reflink.c
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@@ -59,6 +59,50 @@ struct reflink_state_s {
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 typedef struct reflink_state_s * reflink_state;
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+/*
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+ * bsearch_r: implements a re-entrant version of stdlib's bsearch.
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+ * code taken and adapted from /usr/include/bits/stdlib-bsearch.h
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+ */
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+inline void *
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+bsearch_r (const void *__key, const void *__base, size_t __nmemb, size_t __size,
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+	 __compar_d_fn_t __compar, void *__arg)
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+{
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+  size_t __l, __u, __idx;
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+  const void *__p;
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+  int __comparison;
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+
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+  __l = 0;
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+  __u = __nmemb;
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+  while (__l < __u)
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+    {
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+      __idx = (__l + __u) / 2;
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+      __p = (const void *) (((const char *) __base) + (__idx * __size));
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+      __comparison = (*__compar) (__key, __p, __arg);
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+      if (__comparison < 0)
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+	__u = __idx;
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+      else if (__comparison > 0)
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+	__l = __idx + 1;
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+      else
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+	{
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+#if __GNUC_PREREQ(4, 6)
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+# pragma GCC diagnostic push
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+# pragma GCC diagnostic ignored "-Wcast-qual"
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+#endif
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+	  return (void *) __p;
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+#if __GNUC_PREREQ(4, 6)
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+# pragma GCC diagnostic pop
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+#endif
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+	}
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+    }
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+
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+  return NULL;
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+}
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+
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+static int cmpdigest(const void *k1, const void *k2, void *data) {
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+    rpmlog(RPMLOG_DEBUG, _("reflink: cmpdigest k1=%p k2=%p\n"), k1, k2);
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+    return memcmp(k1, k2, *(int *)data);
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+}
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+
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 static int inodeCmp(rpm_ino_t a, rpm_ino_t b)
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 {
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     return (a != b);
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@@ -198,21 +242,13 @@ static rpmRC reflink_psm_post(rpmPlugin plugin, rpmte te, int res)
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 rpm_loff_t find(const unsigned char *digest, reflink_state state);
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 rpm_loff_t find(const unsigned char *digest, reflink_state state) {
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-# if defined(__GNUC__)
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-    /* GCC nested function because bsearch's comparison function can't access
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-     * state-keysize otherwise
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-     */
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-    int cmpdigest(const void *k1, const void *k2) {
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-	rpmlog(RPMLOG_DEBUG, _("reflink: cmpdigest k1=%p k2=%p\n"), k1, k2);
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-	return memcmp(k1, k2, state->keysize);
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-    }
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-# endif
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     rpmlog(RPMLOG_DEBUG,
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-	   _("reflink: bsearch(key=%p, base=%p, nmemb=%d, size=%lu)\n"),
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+	   _("reflink: bsearch_r(key=%p, base=%p, nmemb=%d, size=%lu)\n"),
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 	   digest, state->table, state->keys,
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 	   state->keysize + sizeof(rpm_loff_t));
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-    char *entry = bsearch(digest, state->table, state->keys,
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-			  state->keysize + sizeof(rpm_loff_t), cmpdigest);
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+    char *entry = bsearch_r(digest, state->table, state->keys,
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+			    state->keysize + sizeof(rpm_loff_t), cmpdigest,
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+			    &state->keysize);
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     if (entry == NULL) {
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 	return NOT_FOUND;
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     }
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-- 
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2.35.1
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