diff options
| -rw-r--r-- | Documentation/sysctl/kernel.txt | 25 | ||||
| -rw-r--r-- | lib/vsprintf.c | 33 |
2 files changed, 48 insertions, 10 deletions
diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt index 6d78841fd41..99d8ab9d383 100644 --- a/Documentation/sysctl/kernel.txt +++ b/Documentation/sysctl/kernel.txt @@ -284,13 +284,24 @@ Default value is "/sbin/hotplug". kptr_restrict: This toggle indicates whether restrictions are placed on -exposing kernel addresses via /proc and other interfaces. When -kptr_restrict is set to (0), there are no restrictions. When -kptr_restrict is set to (1), the default, kernel pointers -printed using the %pK format specifier will be replaced with 0's -unless the user has CAP_SYSLOG. When kptr_restrict is set to -(2), kernel pointers printed using %pK will be replaced with 0's -regardless of privileges. +exposing kernel addresses via /proc and other interfaces. + +When kptr_restrict is set to (0), the default, there are no restrictions. + +When kptr_restrict is set to (1), kernel pointers printed using the %pK +format specifier will be replaced with 0's unless the user has CAP_SYSLOG +and effective user and group ids are equal to the real ids. This is +because %pK checks are done at read() time rather than open() time, so +if permissions are elevated between the open() and the read() (e.g via +a setuid binary) then %pK will not leak kernel pointers to unprivileged +users. Note, this is a temporary solution only. The correct long-term +solution is to do the permission checks at open() time. Consider removing +world read permissions from files that use %pK, and using dmesg_restrict +to protect against uses of %pK in dmesg(8) if leaking kernel pointer +values to unprivileged users is a concern. + +When kptr_restrict is set to (2), kernel pointers printed using +%pK will be replaced with 0's regardless of privileges. ============================================================== diff --git a/lib/vsprintf.c b/lib/vsprintf.c index abbabec9720..73e2c45acfd 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -25,6 +25,7 @@ #include <linux/kallsyms.h> #include <linux/uaccess.h> #include <linux/ioport.h> +#include <linux/cred.h> #include <net/addrconf.h> #include <asm/page.h> /* for PAGE_SIZE */ @@ -930,11 +931,37 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr, spec.field_width = 2 * sizeof(void *); return string(buf, end, "pK-error", spec); } - if (!((kptr_restrict == 0) || - (kptr_restrict == 1 && - has_capability_noaudit(current, CAP_SYSLOG)))) + + switch (kptr_restrict) { + case 0: + /* Always print %pK values */ + break; + case 1: { + /* + * Only print the real pointer value if the current + * process has CAP_SYSLOG and is running with the + * same credentials it started with. This is because + * access to files is checked at open() time, but %pK + * checks permission at read() time. We don't want to + * leak pointer values if a binary opens a file using + * %pK and then elevates privileges before reading it. + */ + const struct cred *cred = current_cred(); + + if (!has_capability_noaudit(current, CAP_SYSLOG) || + (cred->euid != cred->uid) || + (cred->egid != cred->gid)) + ptr = NULL; + break; + } + case 2: + default: + /* Always print 0's for %pK */ ptr = NULL; + break; + } break; + case 'N': switch (fmt[1]) { case 'F': |