From 3e5903eb9cff707301712498aed9e34b3e2ee883 Mon Sep 17 00:00:00 2001 From: Petr Mladek Date: Wed, 17 Apr 2019 13:53:48 +0200 Subject: vsprintf: Prevent crash when dereferencing invalid pointers We already prevent crash when dereferencing some obviously broken pointers. But the handling is not consistent. Sometimes we print "(null)" only for pure NULL pointer, sometimes for pointers in the first page and sometimes also for pointers in the last page (error codes). Note that printk() call this code under logbuf_lock. Any recursive printks are redirected to the printk_safe implementation and the messages are stored into per-CPU buffers. These buffers might be eventually flushed in printk_safe_flush_on_panic() but it is not guaranteed. This patch adds a check using probe_kernel_read(). It is not a full-proof test. But it should help to see the error message in 99% situations where the kernel would silently crash otherwise. Also it makes the error handling unified for "%s" and the many %p* specifiers that need to read the data from a given address. We print: + (null) when accessing data on pure pure NULL address + (efault) when accessing data on an invalid address It does not affect the %p* specifiers that just print the given address in some form, namely %pF, %pf, %pS, %ps, %pB, %pK, %px, and plain %p. Note that we print (efault) from security reasons. In fact, the real address can be seen only by %px or eventually %pK. Link: http://lkml.kernel.org/r/20190417115350.20479-9-pmladek@suse.com To: Rasmus Villemoes Cc: Linus Torvalds Cc: "Tobin C . Harding" Cc: Joe Perches Cc: Andrew Morton Cc: Michal Hocko Cc: Steven Rostedt Cc: Sergey Senozhatsky Cc: linux-kernel@vger.kernel.org Reviewed-by: Sergey Senozhatsky Reviewed-by: Andy Shevchenko Signed-off-by: Petr Mladek --- lib/test_printf.c | 22 +++++++++++++++++++++- 1 file changed, 21 insertions(+), 1 deletion(-) (limited to 'lib/test_printf.c') diff --git a/lib/test_printf.c b/lib/test_printf.c index 250ee864b8b8..359ae4fb1ece 100644 --- a/lib/test_printf.c +++ b/lib/test_printf.c @@ -239,6 +239,7 @@ plain_format(void) #define PTR ((void *)0x456789ab) #define PTR_STR "456789ab" #define PTR_VAL_NO_CRNG "(ptrval)" +#define ZEROS "" static int __init plain_format(void) @@ -268,7 +269,6 @@ plain_hash_to_buffer(const void *p, char *buf, size_t len) return 0; } - static int __init plain_hash(void) { @@ -325,6 +325,24 @@ test_hashed(const char *fmt, const void *p) test(buf, fmt, p); } +static void __init +null_pointer(void) +{ + test_hashed("%p", NULL); + test(ZEROS "00000000", "%px", NULL); + test("(null)", "%pE", NULL); +} + +#define PTR_INVALID ((void *)0x000000ab) + +static void __init +invalid_pointer(void) +{ + test_hashed("%p", PTR_INVALID); + test(ZEROS "000000ab", "%px", PTR_INVALID); + test("(efault)", "%pE", PTR_INVALID); +} + static void __init symbol_ptr(void) { @@ -571,6 +589,8 @@ static void __init test_pointer(void) { plain(); + null_pointer(); + invalid_pointer(); symbol_ptr(); kernel_ptr(); struct_resource(); -- cgit v1.2.3