Re: curedump configuration additions

[Michael Miller <michaelm@mjmm.org>]

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Hi.

I have added 

kernel.coredump_suid_enabled

which will allow the generation of core dumps for SUID processes.  (Defaults
to off).

Also I changed the default logging to off, as suggested to avoid 
a posible DOS.

Finally I have changed the logging messages to include EUID and EGID if 
different from UID/GID.

I am keen to try to create a similar feature set to Solaris's coreadm,
but at this stage I am not sure of how would be best to go about doing this...

Adding a 
  /proc/${PID}/coredump
file perhaps- the the kernel source seems to indicate this would be a bad 
thing to do...

Try to implement some new syscalls perhaps?  That sounds quite complex to
me...  Also, would involve using a usermode program to interface... I'd
prefer being able to cat something into /proc

any advise would be greatly appreciated.

attached please find the new patch i

(PS: is an attachment prefered or simply put the patch in the message?)
Mike
 
> Hi,
> 
> I have added some configuration options to the coredump abilities of the 
> kernel. Please can this patch be considered for addition to the kernel.
> 
> I have added three sysctl variables which control the 'features' I 
> have added.  These are:
> 
> kernel.coredump_enabled
> kernel.coredump_log
> kernel.coredump_file_name
> 
> The first two are 'boolean' options which control if the creation of
> core files is globally enabled and if corefile generation if logged
> respectively.
> 
> The third option controls the filename of the coredump.  It allows the use
> of a few tokens within the filename.
> 
> Please find the patch below and attached for convenience.  This is a diff
> against a 2.4.4 kernel.
> 
> Many thanks
> mike
> 

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diff -ru -x *.o -x *.s -x *.flags -x *.a -x *.map -x *.depend linux-2.4.4-orig/Documentation/sysctl/kernel.txt linux/Documentation/sysctl/kernel.txt
--- linux-2.4.4-orig/Documentation/sysctl/kernel.txt	Tue Jan 11 02:15:58 2000
+++ linux/Documentation/sysctl/kernel.txt	Mon May  7 23:44:12 2001
@@ -41,6 +41,10 @@
 - shmmax                      [ sysv ipc ]
 - version
 - zero-paged                  [ PPC only ]
+- coredump_enabled
+- coredump_file_name          
+- coredump_log
+- coredump_suid_enabled
 
 ==============================================================
 
@@ -226,3 +230,68 @@
 the idle loop, possibly speeding up get_free_pages. Since
 this only affects what the idle loop is doing, you should
 enable this and see if anything changes.
+
+==============================================================
+
+coredump_enabled:
+
+When enabled (which is the default), Linux will produce
+coredumps.  This mimics the previous behavior.  Coredumps 
+will not be produced if processes have had their coredump
+limit set.
+
+If disabled, no coredumps will be produced at all.  This is
+useful for systems where increased security is needed so
+that coredumps are not produced, or for systems where coredumps
+are unwanted due to disk space shortages.  I'm sure there are
+other reasons why you would want to disable coredumps too...
+
+==============================================================
+
+coredump_file_name:
+
+Coredump filenames are now configurable using this sysctl.
+
+For starters, to set the variable to emulate previous behavior (which
+is still the default) you need to do:
+  sysctl -w kernel.coredump_filename=core
+
+The filename can either be a relative or absolute filename. The filename
+can contain meta characters which will be expanded when the corefile is
+written.  The meta characters are:
+
+ %c  which is expanded to the process's command name
+ %p  which is expanded to the process's PID
+ %u  which is expanded to the process's UID
+ %U  which is expanded to the process's EUID
+ %g  which is expanded to the process's GID
+ %G  which is expanded to the process's EGID
+
+Note that this is a global setting, so all coredumps are affected by
+this.  A future modification would be to enable per process coredump
+parameters.
+
+==============================================================
+
+coredump_log:
+
+This controls if coredumps get logged by the kernel.  Note that even
+if coredump_enabled=0, you can still log attempts to generate a coredump.
+
+This sysctl variable is useful on machines which may be targets of hacking.
+Hackers may cause a process to crash and generate a coredump.  This option
+allows such events to be logged, and hopefully alert sysadmins to hack
+attempts.
+
+The default is not to log coredumps.
+
+==============================================================
+
+coredump_suid_enabled:
+
+This controls if coredumps are generated for SUID programs.
+
+The default is to not generate core dumps for SUID programs.
+
+==============================================================
+
diff -ru -x *.o -x *.s -x *.flags -x *.a -x *.map -x *.depend linux-2.4.4-orig/fs/exec.c linux/fs/exec.c
--- linux-2.4.4-orig/fs/exec.c	Sat May  5 14:01:45 2001
+++ linux/fs/exec.c	Mon May  7 18:51:21 2001
@@ -20,6 +20,11 @@
  * table to check for several different types  of binary formats.  We keep
  * trying until we recognize the file or we run out of supported binary
  * formats. 
+ *
+ * Configurable coredump_file_name, coredump_log and coredump_enabled 
+ * coredump_suid_enabled support added by Michael Miller,
+ * May 2001, michael@mjmm.org
+ *
  */
 
 #include <linux/config.h>
@@ -48,6 +53,11 @@
 static struct linux_binfmt *formats;
 static rwlock_t binfmt_lock = RW_LOCK_UNLOCKED;
 
+int coredump_enabled = 1;
+char coredump_file_name[256] = "core";
+int coredump_log = 0;
+int coredump_suid_enabled = 0;
+
 int register_binfmt(struct linux_binfmt * fmt)
 {
 	struct linux_binfmt ** tmp = &formats;
@@ -924,26 +934,85 @@
 int do_coredump(long signr, struct pt_regs * regs)
 {
 	struct linux_binfmt * binfmt;
-	char corename[6+sizeof(current->comm)];
+	char corename[256]="";
+	char tmpbuf[256]="\n";
 	struct file * file;
 	struct inode * inode;
+        int i,j,k;
+
+	/* Calculate the min buffer free to handle an expanded token from
+	   coredump_file_name. 22 comes from the max number of digits 
+	   for a 64bit integer.
+	*/
+	k=sizeof(current->comm);
+	if (k<22) 
+		k=22;
+	k=sizeof(corename) - k;
 
 	lock_kernel();
+
+	sprintf(tmpbuf, "process %s, pid %d, uid %d, gid %d",
+		current->comm,current->pid,current->uid,current->gid);
+	if ( (current->uid != current->euid) || 
+		(current->gid != current->egid) ) {
+		sprintf(&tmpbuf[strlen(tmpbuf)], ", euid %d, egid %d",
+			current->euid,current->egid);
+	}
+
+	if (!coredump_enabled)
+		goto fail;
 	binfmt = current->binfmt;
 	if (!binfmt || !binfmt->core_dump)
 		goto fail;
-	if (!current->dumpable || atomic_read(&current->mm->mm_users) != 1)
+	if ((!current->dumpable && !coredump_suid_enabled)
+             || atomic_read(&current->mm->mm_users) != 1)
 		goto fail;
 	current->dumpable = 0;
 	if (current->rlim[RLIMIT_CORE].rlim_cur < binfmt->min_coredump)
 		goto fail;
 
-	memcpy(corename,"core.", 5);
-#if 0
-	memcpy(corename+5,current->comm,sizeof(current->comm));
-#else
-	corename[4] = '\0';
-#endif
+	j=0;
+	for (i=0; (coredump_file_name[i] != '\0') && 
+			(j<k); i++) {
+        	if ( coredump_file_name[i] != '%' ) {
+			corename[j]=coredump_file_name[i];
+			j++;
+		} else {
+			switch(coredump_file_name[++i]) {
+			case 'c':
+				j += sprintf(&corename[j],"%s", current->comm);
+				break;
+			case 'g':
+				j += sprintf(&corename[j],"%u", current->gid);
+				break;
+			case 'G': 
+				j += sprintf(&corename[j],"%u", current->egid);
+				break;
+			case 'p':
+				j += sprintf(&corename[j],"%u", current->pid);
+				break;
+			case 'u':
+				j += sprintf(&corename[j],"%u", current->uid);
+				break;
+			case 'U': 
+				j += sprintf(&corename[j],"%u", current->euid);
+				break;
+			case '%': 
+				corename[j++]=coredump_file_name[i];;
+				break;
+			default: 
+				corename[j++]=coredump_file_name[--i];
+			}
+		}
+	
+        }
+
+	if (j==0) { 
+		memcpy(corename,"core",4);
+		j=4;
+	}
+	corename[j] = '\0';
+
 	file = filp_open(corename, O_CREAT | 2 | O_NOFOLLOW, 0600);
 	if (IS_ERR(file))
 		goto fail;
@@ -963,13 +1032,20 @@
 		goto close_fail;
 	if (!binfmt->core_dump(signr, regs, file))
 		goto close_fail;
+	if (coredump_log) 
+		printk("Coredump to file %s for %s", corename, tmpbuf);
 	unlock_kernel();
 	filp_close(file, NULL);
 	return 1;
 
 close_fail:
 	filp_close(file, NULL);
+	if (coredump_log && (corename[0]!='\0'))
+		printk("Coredump failed to dump to file %s\n",corename); 
+	
 fail:
+	if (coredump_log) 
+		printk("Coredump not dumped for %s\n", tmpbuf);
 	unlock_kernel();
 	return 0;
 }
diff -ru -x *.o -x *.s -x *.flags -x *.a -x *.map -x *.depend linux-2.4.4-orig/include/linux/sysctl.h linux/include/linux/sysctl.h
--- linux-2.4.4-orig/include/linux/sysctl.h	Sat May  5 14:01:49 2001
+++ linux/include/linux/sysctl.h	Mon May  7 18:44:28 2001
@@ -118,7 +118,11 @@
 	KERN_SHMPATH=48,	/* string: path to shm fs */
 	KERN_HOTPLUG=49,	/* string: path to hotplug policy agent */
 	KERN_IEEE_EMULATION_WARNINGS=50, /* int: unimplemented ieee instructions */
-	KERN_S390_USER_DEBUG_LOGGING=51  /* int: dumps of user faults */
+	KERN_S390_USER_DEBUG_LOGGING=51,  /* int: dumps of user faults */
+	KERN_COREDUMP_ENABLED=52, /* are coredumps enabled on this system */
+	KERN_COREDUMP_FILE_NAME=53, /*file name format of coredump files */
+	KERN_COREDUMP_LOG=54,    /*should coredumps get logged */
+	KERN_COREDUMP_SUID_ENABLED=55 /* are suid coredumps enabled */
 };
 
 
diff -ru -x *.o -x *.s -x *.flags -x *.a -x *.map -x *.depend linux-2.4.4-orig/kernel/sysctl.c linux/kernel/sysctl.c
--- linux-2.4.4-orig/kernel/sysctl.c	Sat May  5 14:01:50 2001
+++ linux/kernel/sysctl.c	Mon May  7 18:45:29 2001
@@ -16,6 +16,8 @@
  *  Wendling.
  * The list_for_each() macro wasn't appropriate for the sysctl loop.
  *  Removed it and replaced it with older style, 03/23/00, Bill Wendling
+ * Added coredump_enable, coredump_log, coredump_file_name 2001/05/05,
+ *  Michael Miller
  */
 
 #include <linux/config.h>
@@ -47,6 +49,10 @@
 extern int max_threads;
 extern int nr_queued_signals, max_queued_signals;
 extern int sysrq_enabled;
+extern int coredump_enabled;
+extern int coredump_log;
+extern char coredump_file_name[];
+extern int coredump_suid_enabled;
 
 /* this is needed for the proc_dointvec_minmax for [fs_]overflow UID and GID */
 static int maxolduid = 65535;
@@ -249,6 +255,14 @@
 	{KERN_S390_USER_DEBUG_LOGGING,"userprocess_debug",
 	 &sysctl_userprocess_debug,sizeof(int),0644,NULL,&proc_dointvec},
 #endif
+	{KERN_COREDUMP_ENABLED,"coredump_enabled",&coredump_enabled,
+	sizeof(int), 0644, NULL, &proc_dointvec},
+	{KERN_COREDUMP_FILE_NAME,"coredump_file_name",&coredump_file_name,256,
+	0644,NULL,&proc_dostring, &sysctl_string},
+	{KERN_COREDUMP_LOG,"coredump_log",&coredump_log,
+	sizeof(int), 0644, NULL, &proc_dointvec},
+	{KERN_COREDUMP_SUID_ENABLED,"coredump_suid_enabled",
+	&coredump_suid_enabled,sizeof(int), 0644, NULL, &proc_dointvec},
 	{0}
 };