jesec-rtorrent: Add patch to prevent segfault

From dd4a96073d4a60ca8fff55be6ea6b17018de96a8 Mon Sep 17 00:00:00 2001

From: Varun Madiath <git@madiathv.com>

Date: Wed, 19 Jul 2023 15:30:57 -0400

Subject: [PATCH] utils: lockfile: avoid stack overflow for lockfile buffer

Original patch by @cyphar was submitted to rakshasa/rtorrent at

https://github.com/rakshasa/rtorrent/pull/1169.

Observed the segfault on nixos-unstable.

---

 src/utils/lockfile.cc | 3 ++-

 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/utils/lockfile.cc b/src/utils/lockfile.cc

index 76e4b8f..441f5c8 100644

--- a/src/utils/lockfile.cc

+++ b/src/utils/lockfile.cc

@@ -75,7 +75,8 @@ Lockfile::try_lock() {

   int  pos = ::gethostname(buf, 255);

   if (pos == 0) {

-    ::snprintf(buf + std::strlen(buf), 255, ":+%i\n", ::getpid());

+    ssize_t len = std::strlen(buf);

+    ::snprintf(buf + len, 255 - len, ":+%i\n", ::getpid());

     ssize_t __attribute__((unused)) result = ::write(fd, buf, std::strlen(buf));

   }

-- 

2.41.0

    hash = "sha256-i7c1jSawHshj1kaXl8tdpelIKU24okeg9K5/+ht6t2k=";

  };

  patches = [

    ./avoid-stack-overflow-for-lockfile-buf.patch

  ];

  passthru = {

    inherit libtorrent;

  };