clang compiler warnings: Fix autological comparisons

This fixes autological comparison warnings in the following:
 * chan_skinny: letohl may return a signed or unsigned value, depending on the
   macro chosen
 * func_curl: Provide a specific cast to CURLoption to prevent mismatch
 * cel: Fix enum comparisons where the enum can never be negative
 * enum: Fix comparison of return result of dn_expand, which returns a signed
   int value
 * event: Fix enum comparisons where the enum can never be negative
 * indications: tone_data.freq1 and freq2 are unsigned, and hence can never be
   negative
 * presencestate: Use the actual enum value for INVALID state
 * security_events: Fix enum comparisons where the enum can never be negative
 * udptl: Don't bother to check if the return value from encode_length is less
   than 0, as it returns an unsigned int
 * translate: Since the parameters are unsigned int, don't bother checking
   to see if they are negative. The cast to unsigned int would already blow
   past the matrix bounds.
 * res_pjsip_exten_state: Use a temporary value to cache the return of
   ast_hint_presence_state
 * res_stasis_playback: Fix enum comparisons where the enum can never be
   negative
 * res_stasis_recording: Add an enum value for the case where the recording
   operation is in error; fix enum comparisons
 * resource_bridges: Use enum value as opposed to -1
 * resource_channels: Use enum value as opposed to -1

Review: https://reviewboard.asterisk.org/r/4533
ASTERISK-24917
Reported by: dkdegroot
patches:
  rb4533.patch submitted by dkdegroot (License 6600)
........

Merged revisions 434469 from http://svn.asterisk.org/svn/asterisk/branches/11
........

Merged revisions 434470 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@434471 65c4cc65-6c06-0410-ace0-fbb531ad65f3

1 files changed, 5 insertions, 1 deletions

diff --git a/channels/chan_skinny.c b/channels/chan_skinny.c
index 3d56cc840..d1c05abec 100644
--- a/channels/chan_skinny.c
+++ b/channels/chan_skinny.c
@@ -2374,6 +2374,7 @@ static char *callstate2str(int ind)
 static int transmit_response_bysession(struct skinnysession *s, struct skinny_req *req)
 {
 	int res = 0;
+	unsigned long len;
 
 	if (!s) {
 		ast_log(LOG_WARNING, "Asked to transmit to a non-existent session!\n");
@@ -2382,7 +2383,10 @@ static int transmit_response_bysession(struct skinnysession *s, struct skinny_re
 
 	ast_mutex_lock(&s->lock);
 
-	if ((letohl(req->len) > SKINNY_MAX_PACKET) || (letohl(req->len) < 0)) {
+	/* Don't optimize out assigning letohl() to len. It is necessary to guarantee that the comparison will always catch invalid values.
+	 * letohl() may or may not return a signed value depending upon which definition is used. */
+	len = letohl(req->len);
+	if (SKINNY_MAX_PACKET < len) {
 		ast_log(LOG_WARNING, "transmit_response: the length of the request (%u) is out of bounds (%d)\n", letohl(req->len), SKINNY_MAX_PACKET);
 		ast_mutex_unlock(&s->lock);
 		return -1;