* [PATCH] spawn (Inline::C): fix off-by-one error
@ 2019-05-07 0:28 Eric Wong
0 siblings, 0 replies; only message in thread
From: Eric Wong @ 2019-05-07 0:28 UTC (permalink / raw)
To: meta
Noticed while testing on FreeBSD 11.2 amd64 with the optional
Inline::C extension using clang 6.0.0. The end result on
FreeBSD was spawning processes failed badly and things were
immediately unusable with this enabled.
av_len is a misleading API, and I failed to read the API
comments in perl:/av.c which state:
> Note that, unlike what the name implies, it returns
> the highest index in the array, so to get the size of
> the array you need to use "av_len(av) + 1".
> This is unlike "sv_len", which returns what you would expect.
If this bug affected anybody, it would've only affected users
using both the optional Inline::C module AND set the
PERL_INLINE_DIRECTORY environment variable.
That said, I've never seen any evidence of it on Debian
GNU/Linux + gcc on any x86 variant. That includes full 64-bit
systems, a full 32-bit system, a 64-bit system with 32-bit
userspace, across multiple gcc versions since 2016.
---
lib/PublicInbox/Spawn.pm | 47 ++++++++++++++++++++++++----------------
1 file changed, 28 insertions(+), 19 deletions(-)
diff --git a/lib/PublicInbox/Spawn.pm b/lib/PublicInbox/Spawn.pm
index 7b0f3bd..66b916d 100644
--- a/lib/PublicInbox/Spawn.pm
+++ b/lib/PublicInbox/Spawn.pm
@@ -26,22 +26,35 @@ my $vfork_spawn = <<'VFORK_SPAWN';
#include <sys/time.h>
#include <sys/resource.h>
#include <unistd.h>
-#include <alloca.h>
-#include <signal.h>
-#include <assert.h>
+#include <stdlib.h>
-#define AV_ALLOCA(av, max) alloca((max = (av_len((av)) + 1)) * sizeof(char *))
+/* some platforms need alloca.h, but some don't */
+#if defined(__GNUC__) && !defined(alloca)
+# define alloca(sz) __builtin_alloca(sz)
+#endif
-static void av2c_copy(char **dst, AV *src, I32 max)
-{
- I32 i;
+#include <signal.h>
+#include <assert.h>
- for (i = 0; i < max; i++) {
- SV **sv = av_fetch(src, i, 0);
- dst[i] = sv ? SvPV_nolen(*sv) : 0;
- }
- dst[max] = 0;
-}
+/*
+ * From the av_len apidoc:
+ * Note that, unlike what the name implies, it returns
+ * the highest index in the array, so to get the size of
+ * the array you need to use "av_len(av) + 1".
+ * This is unlike "sv_len", which returns what you would expect.
+ */
+#define AV2C_COPY(dst, src) do { \
+ I32 i; \
+ I32 top_index = av_len(src); \
+ I32 real_len = top_index + 1; \
+ I32 capa = real_len + 1; \
+ dst = alloca(capa * sizeof(char *)); \
+ for (i = 0; i < real_len; i++) { \
+ SV **sv = av_fetch(src, i, 0); \
+ dst[i] = SvPV_nolen(*sv); \
+ } \
+ dst[real_len] = 0; \
+} while (0)
static void *deconst(const char *s)
{
@@ -86,15 +99,11 @@ int pi_fork_exec(int in, int out, int err,
const char *filename = SvPV_nolen(file);
pid_t pid;
char **argv, **envp;
- I32 max;
sigset_t set, old;
int ret, errnum;
- argv = AV_ALLOCA(cmd, max);
- av2c_copy(argv, cmd, max);
-
- envp = AV_ALLOCA(env, max);
- av2c_copy(envp, env, max);
+ AV2C_COPY(argv, cmd);
+ AV2C_COPY(envp, env);
ret = sigfillset(&set);
assert(ret == 0 && "BUG calling sigfillset");
--
EW
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2019-05-07 0:28 [PATCH] spawn (Inline::C): fix off-by-one error Eric Wong
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