Re: [Crash-utility] [PATCH] Fix live debugging with lockdown=integrity

From: Philipp Rudo <prudo(a)redhat.com&gt; To: crash-utility(a)redhat.com Subject: [Crash-utility] [PATCH] Fix live debugging with lockdown=integrity Message-ID: <20211109135222.51636-1-prudo(a)redhat.com&gt; With kernel lockdown the access to kernel interfaces that allow to extract confidential information (lockdown=confidentiality) or modify a running kernel (lockdown=integrity) can be restricted. Two of the interfaces that can be restricted are /dev/mem (integrity & confidentiality) and /proc/kcore (confidentiality). With lockdown=integrity this leads to a situation where /dev/mem exists but is not readable while /proc/kcore exists and is readable. This breaks crash's live debugging when it is invoked without argument, i.e. $ crash [...] crash: /dev/mem: Operation not permitted while passing /proc/kcore as image succeeds. The reason for this is that crash always picks /dev/mem as source when it exits but doesn't check if it is readable. Fix this by only selecting /dev/mem when it is readable. Signed-off-by: Philipp Rudo <prudo(a)redhat.com&gt; --- filesys.c | 2 +- main.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/filesys.c b/filesys.c index 3361b6c..43cbe82 100644 --- a/filesys.c +++ b/filesys.c @@ -3666,7 +3666,7 @@ get_live_memory_source(void) if (pc->live_memsrc) goto live_report; - if (file_exists("/dev/mem", NULL)) + if (file_readable("/dev/mem")) pc->live_memsrc = "/dev/mem"; else if (file_exists("/proc/kcore", NULL)) { pc->flags &= ~DEVMEM; diff --git a/main.c b/main.c index 71c59d2..b278c22 100644 --- a/main.c +++ b/main.c @@ -1119,7 +1119,7 @@ setup_environment(int argc, char **argv) pc->flags2 |= REDZONE; pc->confd = -2; pc->machine_type = MACHINE_TYPE; - if (file_exists("/dev/mem", NULL)) { /* defaults until argv[] is parsed */ + if (file_readable("/dev/mem")) { /* defaults until argv[] is parsed */ pc->readmem = read_dev_mem; pc->writemem = write_dev_mem; } else if (file_exists("/proc/kcore", NULL)) { -- 2.31.1