Messages in this thread Patch in this message |  | | From | Petr Mladek <> | Subject | [PATCH v4 2/9] vsprintf: Consistent %pK handling for kptr_restrict == 0 | Date | Wed, 4 Apr 2018 10:58:36 +0200 |
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restricted_pointer() pretends that it prints the address when kptr_restrict is set to zero. But it is never called in this situation. Instead, pointer() falls back to ptr_to_id() and hashes the pointer.
This patch removes the potential confusion. klp_restrict is checked only in restricted_pointer().
It should actually fix a small race when the address might get printed unhashed:
CPU0 CPU1
pointer() if (!kptr_restrict) /* for example set to 2 */ restricted_pointer() /* echo 0 >/proc/sys/kernel/kptr_restrict */ proc_dointvec_minmax_sysadmin() klpr_restrict = 0; switch(kptr_restrict) case 0: break:
number()
Fixes: commit ef0010a30935de4e0211 ("vsprintf: don't use 'restricted_pointer()' when not restricting") Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Tobin Harding <me@tobin.cc> Cc: Kees Cook <keescook@chromium.org> Signed-off-by: Petr Mladek <pmladek@suse.com> --- lib/vsprintf.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-)
diff --git a/lib/vsprintf.c b/lib/vsprintf.c index c0c677c6a833..9ade2c4f21ba 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -637,7 +637,8 @@ static int __init initialize_ptr_random(void) early_initcall(initialize_ptr_random); /* Maps a pointer to a 32 bit unique identifier. */ -static char *ptr_to_id(char *buf, char *end, void *ptr, struct printf_spec spec) +static char *ptr_to_id(char *buf, char *end, + const void *ptr, struct printf_spec spec) { unsigned long hashval; const int default_width = 2 * sizeof(ptr); @@ -1426,8 +1427,8 @@ char *restricted_pointer(char *buf, char *end, const void *ptr, switch (kptr_restrict) { case 0: - /* Always print %pK values */ - break; + /* Handle as %p, hash and do _not_ leak addresses. */ + return ptr_to_id(buf, end, ptr, spec); case 1: { const struct cred *cred; @@ -1931,8 +1932,6 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr, return buf; } case 'K': - if (!kptr_restrict) - break; return restricted_pointer(buf, end, ptr, spec); case 'N': return netdev_bits(buf, end, ptr, fmt); -- 2.13.6
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