Hi, On Mon, Jun 30, 2025 at 11:36:59PM +0100, Andrew Bower wrote: > Running 'w' as a non-root user on i386 segfaults: > > $ gdb w > GNU gdb (Debian 16.3-1) 16.3 > [...] > This GDB was configured as "i686-linux-gnu". > [...] > (gdb) run > Starting program: /usr/bin/w > [Thread debugging using libthread_db enabled] > Using host libthread_db library "/lib/i386-linux-gnu/libthread_db.so.1". > 23:21:56 up 4 min, 0 users, load average: 0.74, 1.06, 0.52 > USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT > > Program received signal SIGSEGV, Segmentation fault. > Download failed: Invalid argument. Continuing without source file ./src/w.c. > 0x00401979 in main (argc=<optimized out>, argv=<optimized out>) at > src/w.c:1130 > warning: 1130 src/w.c: No such file or directory > > This reliably reproduces in the failing environment but not when run as root > or > on an amd64 host with kernel 6.12.27-1.
The proximate cause seems to be that sessions is undefined and that sessions_list is then also used, undefined. This part of the bug is therefore not architecture-specific even if the crash is not generally reproduced yet. I attach a patch that fixes the segfault to advance the discussion. Personally I think this ought to be fixed for trixie. However, we are unfortunately not out of the woods: elogind is running on this host and root is able to see the sessions. So is 'who' as non-root with the newly libsystemd-ised coreutils: $ w 21:26:33 up 10 min, 0 users, load average: 0.00, 0.10, 0.12 USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT Segmentation fault $ debian/procps/usr/bin/w # with patch 21:26:42 up 11 min, 0 users, load average: 0.00, 0.10, 0.12 USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT $ sudo w Please touch the FIDO authenticator. 21:26:50 up 11 min, 1 user, load average: 0.64, 0.23, 0.16 USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT ajb85 pts/0 - 21:26 0.00s 0.03s 0.12s sudo w $ sudo debian/procps/usr/bin/w # with patch 21:26:54 up 11 min, 1 user, load average: 0.59, 0.23, 0.16 USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT ajb85 pts/0 - 21:26 0.00s 0.02s 0.06s sudo debian/procps/usr/bin/w $ who ajb85 seat0 2025-07-23 21:17 ajb85 tty1 2025-07-23 21:17 This secondary issue could of course be an elogingd problem so I am copying this message to the elogind package tracker for awareness. Thanks!
>From 3b519356a12c62e322287a2d0ffa0311da70f8a1 Mon Sep 17 00:00:00 2001 From: Andrew Bower <[email protected]> Date: Wed, 23 Jul 2025 18:27:13 +0100 Subject: [PATCH] Initialise sessions variable in w. (Closes: #1108549) --- debian/patches/w_terminal_mode | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/debian/patches/w_terminal_mode b/debian/patches/w_terminal_mode index 075a14f..e6e5a36 100644 --- a/debian/patches/w_terminal_mode +++ b/debian/patches/w_terminal_mode @@ -19,11 +19,14 @@ Description: w: Add terminal mode screens so its not real big difference. * From/IP won't work for utmp systems . - This patch includes the upstreams original commit and the enhancement. + This patch includes the upstream's original commit and the enhancement. + . + Updated 2025-07-23 to avoid acting on the value of uninitialised sessions + variable. Author: Craig Small <[email protected]> Origin: upstream, https://gitlab.com/procps-ng/procps/-/commit/f53cc24d57085c87ebb1871b92c0069b72a60926 Applied-Upstream: 4.0.6 -Last-Update: 2025-04-14 +Last-Update: 2025-07-23 --- This patch header follows DEP-3: http://dep.debian.net/deps/dep3/ --- a/man/w.1 @@ -485,7 +488,7 @@ This patch header follows DEP-3: http://dep.debian.net/deps/dep3/ + } else { +#if (defined(WITH_SYSTEMD) || defined(WITH_ELOGIND)) && defined(HAVE_SD_SESSION_GET_LEADER) + char **sessions_list; -+ int sessions; ++ int sessions = 0; + if (sd_booted() > 0) sessions = sd_get_sessions (&sessions_list); - if (sessions < 0 && sessions != -ENOENT) -- 2.50.0
