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Commit ee24aebf authored by Linus Torvalds's avatar Linus Torvalds
Browse files

cap_syslog: accept CAP_SYS_ADMIN for now 



In commit ce6ada35 ("security: Define CAP_SYSLOG") Serge Hallyn
introduced CAP_SYSLOG, but broke backwards compatibility by no longer
accepting CAP_SYS_ADMIN as an override (it would cause a warning and
then reject the operation).

Re-instate CAP_SYS_ADMIN - but keeping the warning - as an acceptable
capability until any legacy applications have been updated.  There are
apparently applications out there that drop all capabilities except for
CAP_SYS_ADMIN in order to access the syslog.

(This is a re-implementation of a patch by Serge, cleaning the logic up
and making the code more readable)

Acked-by: default avatarSerge Hallyn <serge@hallyn.com>
Reviewed-by: default avatarJames Morris <jmorris@namei.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 67d01952

kernel/printk.c

+35 −19
Original line number Diff line number Diff line
@@ -262,25 +262,47 @@ int dmesg_restrict = 1; 
int dmesg_restrict;

#endif



static int syslog_action_restricted(int type)

{

	if (dmesg_restrict)

		return 1;

	/* Unless restricted, we allow "read all" and "get buffer size" for everybody */

	return type != SYSLOG_ACTION_READ_ALL && type != SYSLOG_ACTION_SIZE_BUFFER;

}



static int check_syslog_permissions(int type, bool from_file)

{

	/*

	 * If this is from /proc/kmsg and we've already opened it, then we've

	 * already done the capabilities checks at open time.

	 */

	if (from_file && type != SYSLOG_ACTION_OPEN)

		return 0;



	if (syslog_action_restricted(type)) {

		if (capable(CAP_SYSLOG))

			return 0;

		/* For historical reasons, accept CAP_SYS_ADMIN too, with a warning */

		if (capable(CAP_SYS_ADMIN)) {

			WARN_ONCE(1, "Attempt to access syslog with CAP_SYS_ADMIN "

				 "but no CAP_SYSLOG (deprecated).\n");

			return 0;

		}

		return -EPERM;

	}

	return 0;

}



int do_syslog(int type, char __user *buf, int len, bool from_file)

{

	unsigned i, j, limit, count;

	int do_clear = 0;

	char c;

	int error = 0;

	int error;



	/*

	 * If this is from /proc/kmsg we only do the capabilities checks

	 * at open time.

	 */

	if (type == SYSLOG_ACTION_OPEN || !from_file) {

		if (dmesg_restrict && !capable(CAP_SYSLOG))

			goto warn; /* switch to return -EPERM after 2.6.39 */

		if ((type != SYSLOG_ACTION_READ_ALL &&

		     type != SYSLOG_ACTION_SIZE_BUFFER) &&

		    !capable(CAP_SYSLOG))

			goto warn; /* switch to return -EPERM after 2.6.39 */

	}

	error = check_syslog_permissions(type, from_file);

	if (error)

		goto out;



	error = security_syslog(type);

	if (error)
@@ -423,12 +445,6 @@ int do_syslog(int type, char __user *buf, int len, bool from_file) 
	}

out:

	return error;

warn:

	/* remove after 2.6.39 */

	if (capable(CAP_SYS_ADMIN))

		WARN_ONCE(1, "Attempt to access syslog with CAP_SYS_ADMIN "

		  "but no CAP_SYSLOG (deprecated and denied).\n");

	return -EPERM;

}



SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)