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SubjectRe: curedump configuration additions
Date
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
>
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}
};
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